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Look - a shooting star! Learn all about meteors in this article.

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A meteor is a bright streak of light in the sky (a "shooting star" or a "falling star") produced by the entry of a small meteoroid into the Earth's atmosphere. If you have a dark clear sky you will probably see a few per hour on an average night; during one of the annual meteor showers you may see as many as 100/hour.

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Water, frozen gas, and dust have never looked better - read all about comets here!

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Unlike the other small bodies in the solar system, comets have been known since antiquity. There are Chinese records of Comet Halley going back to at least 240 BC

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Bodies of rock out there orbiting the sun - learn more about asteroids.

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Asteroids l Asteroid facts, pictures and information

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Several hundred thousand asteroids have been discovered and given provisional designations so far. Thousands more are discovered each year.

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Surprisingly, not the biggest or brightest star, our Sun just happens to be the closest star. Read more about it here.

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Our Sun is a normal main-sequence G2 star, one of more than 100 billion stars in our galaxy.

The Sun Profile

diameter: 1,390,000 km.
mass: 1.989e30 kg
temperature: 5800 K (surface) 15,600,000 K (core)

History of The Sun

The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest).

It is often said that the Sun is an "ordinary" star. That's true in the sense that there are many others similar to it. But there are many more smaller stars than larger ones; the Sun is in the top 10% by mass. The median size of stars in our galaxy is probably less than half the mass of the Sun.

The Sun is personified in many mythologies: the Greeks called it Helios and the Romans called it Sol.

The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else ("metals") amounts to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.

The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets. The differential rotation extends considerably down into the interior of the Sun but the core of the Sun rotates as a solid body.

Conditions at the Sun's core (approximately the inner 25% of its radius) are extreme. The temperature is 15.6 million Kelvin and the pressure is 250 billion atmospheres. At the center of the core the Sun's density is more than 150 times that of water.

The Sun's power (about 386 billion billion mega Watts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons (=3.86e33 ergs) of energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation.

The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. Sunspots are "cool" regions, only 3800 K (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 km in diameter. Sunspots are caused by complicated and not very well understood interactions with the Sun's magnetic field.

A small region known as the chromosphere lies above the photosphere.

The highly rarefied region above the chromosphere, called the corona, extends millions of kilometers into space but is visible only during a total solar eclipse (left). Temperatures in the corona are over 1,000,000 K.

It just happens that the Moon and the Sun appear the same size in the sky as viewed from the Earth. And since the Moon orbits the Earth in approximately the same plane as the Earth's orbit around the Sun sometimes the Moon comes directly between the Earth and the Sun. This is called a solar eclipse; if the alignment is slighly imperfect then the Moon covers only part of the Sun's disk and the event is called a partial eclipse. When it lines up perfectly the entire solar disk is blocked and it is called a total eclipse of the Sun. Partial eclipses are visible over a wide area of the Earth but the region from which a total eclipse is visible, called the path of totality, is very narrow, just a few kilometers (though it is usually thousands of kilometers long). Eclipses of the Sun happen once or twice a year. If you stay home, you're likely to see a partial eclipse several times per decade. But since the path of totality is so small it is very unlikely that it will cross you home. So people often travel half way around the world just to see a total solar eclipse. To stand in the shadow of the Moon is an awesome experience. For a few precious minutes it gets dark in the middle of the day. The stars come out. The animals and birds think it's time to sleep. And you can see the solar corona. It is well worth a major journey.

The Sun's magnetic field is very strong (by terrestrial standards) and very complicated. Its magnetosphere (also known as the heliosphere) extends well beyond Pluto.

In addition to heat and light, the Sun also emits a low density stream of charged particles (mostly electrons and protons) known as the solar wind which propagates throughout the solar system at about 450 km/sec. The solar wind and the much higher energy particles ejected by solar flares can have dramatic effects on the Earth ranging from power line surges to radio interference to the beautiful aurora borealis.

Recent data from the spacecraft Ulysses show that during the minimum of the solar cycle the solar wind emanating from the polar regions flows at nearly double the rate, 750 kilometers per second, than it does at lower latitudes. The composition of the solar wind also appears to differ in the polar regions. During the solar maximum, however, the solar wind moves at an intermediate speed.

Further study of the solar wind will be done by Wind, ACE and SOHO spacecraft from the dynamically stable vantage point directly between the Earth and the Sun about 1.6 million km from Earth.

The solar wind has large effects on the tails of comets and even has measurable effects on the trajectories of spacecraft.

Spectacular loops and prominences are often visible on the Sun's limb (left).

The Sun's output is not entirely constant. Nor is the amount of sunspot activity. There was a period of very low sunspot activity in the latter half of the 17th century called the Maunder Minimum. It coincides with an abnormally cold period in northern Europe sometimes known as the Little Ice Age. Since the formation of the solar system the Sun's output has increased by about 40%.

The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core. It will continue to radiate "peacefully" for another 5 billion years or so (although its luminosity will approximately double in that time). But eventually it will run out of hydrogen fuel. It will then be forced into radical changes which, though commonplace by stellar standards, will result in the total destruction of the Earth (and probably the creation of a planetary nebula).

The Sun's satellites

There are eight planets and a large number of smaller objects orbiting the Sun. (Exactly which bodies should be classified as planets and which as "smaller objects" has been the source of some controversy, but in the end it is really only a matter of definition. Pluto is no longer officially a planet but we'll keep it here for history's sake.)

More detailed data and definitions of terms can be found on the data page.

More about the Sun

Open Issues

Is there a causal connection between the Maunder Minimum and the Little Ice Age or was it just a coincidence? How does the variability of the Sun affect the Earth's climate?

Since all the planets except Pluto orbit the Sun within a few degrees of the plane of the Sun's equator, we know very little about the interplanetary environment outside that plane. The Ulysses mission will provide information about the polar regions of the Sun.

The corona is much hotter than the photosphere. Why?

Interesting Facts about the Sun

The Sun is one of the millions of stars in the solar system. It is, however, larger than most (although not the biggest) and a very special star to us. Without the Sun there would be absolutely no life on Earth.

The Sun is 870,000 miles (1.4 million kilometers) across. This is so big it is hard to imagine, but it would take more than one million Earths to fill the size of the Sun!

The Sun is so big it takes up 99% of the matter in our solar system. The 1% left over is taken up by planets, asteroids, moons and other matter.

The Sun is about 4.5 billion years old. It is thought to be halfway through its lifetime. Stars get bigger as they get older.

As the Sun ages, it will get bigger. When this happens, it will consume some of the things close to it, and this includes Mercury, Venus and maybe even Earth and Mars. Luckily this is billions of years in the future.

The Sun is the centre of the solar system.

The Sun is 92.96 million miles (149.6 kilometers) away from Earth.

The Sun is made of a ball of burning gases. These gases are 92.1% hydrogen and 7.8% helium.

The sunlight we see on Earth left the Sun 8 minutes ago. This is the length of time it takes for the light to travel the distance between the Sun and the Earth.

When the moon goes around the Earth, it sometimes finds itself between the Earth and the Sun. This is called a solar eclipse and makes the Earth dark whilst the moon shuts out most of the Sun's light. This only lasts for a couple of hours while the moon continues its rotation and moves out of the way of the sun.

In ancient astronomy, it was thought that the Sun moved. People believed that the Earth stayed still and the Sun rotated around it.

About 2000 years ago some began to think it was the Sun that stays still whilst the planets make a path around it. This only became an accepted theory around the 1600s when Isaac Newton proposed the sun-centric solar system.

The Sun is almost a perfect sphere. It is the closest thing to a sphere found in nature with only a 6.2 mile (10 kilometres) difference between its vertical and horizontal measurements.

The Sun's core is extremely hot! An unthinkable 13,600,000 degrees Celcius!

The Sun has a very big magnetic field. It is the most powerful magnetic field in the whole solar system. This field is regenerating itself, but scientists are unsure how.

The Sun produces solar winds. These are a stream of particles from the Sun that stream out into space. This is why planets atmospheres are so important. They protect the planet from these solar winds.

The Sun rotates but not as Earth does. On Earth, the planet is rotating at the same speed no matter where you are. The Sun does not rotate like a solid object and is spinning faster at its equator than it is at its poles. It is complicated to say how fast the Sun is spinning but depending whereabouts on the Sun you are looking at it takes between 24 and 38 days to spin around.

The Sun has been both worshipped and feared throughout history by a variety of cultures.

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The Sun Facts | Information, History, Size, Formation & Definition

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Our Sun is a normal main-sequence G2 star, one of more than 100 billion stars in our galaxy. diameter: 1,390,000 km.mass: 1.989e30 kgtemperature: 5800 K (surface) 15,600,000 K (core) The Sun is by far the largest object in the solar system.

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The Solar System is made up of the planets, but also includes stars - like our Sun, asteroids, comets, meteors, and moons.

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The Outer Planets are Jupiter, Saturn, Neptune, & Uranus - the four farthest planets from the sun.  These are mostly made up of frozen gas and are much larger than the Inner Planets.

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The Inner Planets are Mercury, Venus, Earth, & Mars - which are the four planets closest to the sun. They have rocky surfaces and are much smaller than the Outer Planets.

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Poor Pluto. It used to be a regular planet, but it was demoted to "dwarf planet" because of its small size and inability to command its own orbit.

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Pluto - Educational facts and the history of Pluto.

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Pluto orbits beyond the orbit of Neptune (usually). It is much smaller than any of the official planets and now classified as a "dwarf planet". Pluto is smaller than seven of the solar system's moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton).

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The blue planet - read about Neptune.

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Neptune is the fourth largest and the farthest planet of the Solar System with the most powerful wind speeds out of all the planets. It is the smallest of the gas giants and is the first planet to be discovered by mathematical predictions in 1846.
Key Facts & Summary

It is the only planet that is invisible to the unaided eye, thus it eluded ancient astronomers until it was officially discovered in 1846 by Le Verrier and Johann Galle.

The greatest factor of the discovery was the planet Uranus, whom astronomers were calculating its orbit and observed that Uranus wasn't following their models.

The perturbed orbit of Uranus forced astronomer Urbain Le Verrier to conclude that another undiscovered planet must be at fault. He predicted where it should be, and astronomer Johann Galle found it one degree away from the predicted point thus making Neptune the first planet to be discovered by mathematical calculations and predictions.

Neptune was given the name of the roman god of the sea due to its bluish-ocean like color. Its satellites also received names of water deities.

Neptune's color is believed to be influenced by the presence of methane in its atmosphere and also an unknown factor.

Neptune has an average distance of 2.8 billion miles/4.5 billion kilometers or 30 AU away from the Sun, being the furthest of the eight planets. Currently it is 29.4 AU away from Earth with its light taking up to 4 hours to arrive to us. Neptune's actual position can be checked online as the planet is constantly tracked.

As a result from its distance, it also has the longest orbital duration completing a trip around the Sun in about 165 years.

However, one rotation or day on Neptune is completed in 16 hours.

Until Pluto's eccentric orbit was understood and its status dropped from that of a planet to a dwarf planet, Neptune was considered the second furthest planet from the Sun.

Neptune has a radius of 15.387 miles or 24.764 kilometers, about four times wider than Earth, and a diameter of 49.244 km or 30.598 mi being the fourth largest planet of the solar system.

Neptune and Uranus are termed as ice giants because they are smaller and have different compositionality from the gas giants Jupiter and Saturn. Neptune being made out of layers of helium 29% and 80% hydrogen with traces of methane.

It has a core about 1.5 times the size of Earth with twice its pressure: 7 Mbar or 700 GPa, making up about 45% of the planet's mass, but it does not have a surface.

This is a characteristic of the ice giants, their "rocky", icy cores who are proportionally larger than the amount of gas they contain, unlike the gas giants.

Neptune is the smallest ice giant with a mass of 1.024 × 10^26 kg but has the greatest density out of all the gas giants, about 1.64 g/cm³.

It has an average temperature of -214 degrees Celsius;-353 degrees Fahrenheit, however Uranus is the coldest ice giant, and for that fact the coldest of all planets in the solar system.

Neptune however, excels from something else. It has the fastest wind speed of any planet. Wind speeds blowing westward on the equator reach up to 2,160 kilometers or 1.324 miles per hour, nearly a supersonic flow. Most winds travel retrograde to the rotation of the planet they are 5 times stronger than the strongest winds recorded on Earth, breaking the sound barrier.

Neptune has a total of 6 known rings with some containing ring arcs or clusters of dust particles in a ring.

Neptune also has 14 known moons, the largest is called Triton, and it is the seventh largest known moon of any planet, also being the only one in the solar system that orbits in retrograde or in opposition to the planet's rotation. This means that it is a captured object by Neptune's gravity. Due to its size it is even believed it is a captured dwarf planet.

Neptune was observed in 1613 by Galileo Galilei however, he taught that it was just a star, and when he wanted to further research it, the motion of the planet began to be far too slight to be detected again. The greatest factor of the discovery was the planet Uranus, whom astronomers were calculating its orbit and observed that Uranus wasn't following their models.

The perturbed orbit of Uranus forced astronomers to conclude that another undiscovered planet must be at fault. They predicted where it should be, and astronomer Urbain Le Verrier asked the help of Johann Galle, an astronomer at the Berlin Observatory. Galle found the planet one degree away from the predicted point thus making Neptune the first planet to be discovered by mathematical calculations and predictions.

Galle proposed the name Janus, the Roman god with two faces and La Verrier proposed the name Neptune, however he did tried to name the planet after him but he didn't have popular support outside of France. The astronomer Struve, came out in favor of the name Neptune in December 29 th 1846. Soon after, it became wildly accepted. Neptune was the Roman god of the sea, identified with the Greek Poseidon as the planet appeared water-like in color.

Formation

Through simulations after the Nice model, it has been suggested that both Neptune and Uranus formed closer to the sun and later drifted away. It is hypothesized that the Solar System formed from a giant rotating ball of gas and dust known as the pre-solar nebula.

Much of it formed the Sun while more of its dust went on and merged to create the first proto-planets. As they grew, some accreted enough matter for their gravity to hold unto the nebula's leftover gas. Estimates suggest the creation to have taken place about 4.5 billion years ago, and the drifting about 4 billion.

Distance, Size and Mass

From its discovery until 1930 when Pluto was discovered, Neptune was considered the farthest planet. After the discovery of Pluto, Neptune was thought to be the second furthest planet. When Pluto's eccentric orbit was understood and its status dropped from that of a planet to a dwarf planet in 2006, Neptune regained the title of the farthest planet in Solar System.

Neptune has an average distance of 2.8 billion miles/4.5 billion kilometers or 30.1 AU away from the Sun, and its currently 29.4 AU away from Earth with its light taking up to 4 hours to arrive to us.

The mass of Jupiter is about 17 times that of Earth or 1.0243×10 ²⁶ kg, but when compared to the largest gas giant Jupiter, it has only 1/19 th of Jupiter's mass. It has an equatorial radius of 15.387 miles or 24.764 kilometers, about four times wider than Earth, and a diameter of 49.244 km or 30.598 mi, being the fourth largest planet of the solar system.

Orbit and Rotation

Since it is the farthest planet from the Sun it has the longest orbital duration, completing a trip around the Sun in about 165 years. However, one sidereal rotation or day on Neptune is completed in 16.11 hours.

The average distance from the Sun is about 30.1 AU, while at its perihelion 29.81 AU, and its aphelion 30.33 AU. The elliptical orbit of Neptune is inclined 1.77° compared to that of Earth.

Axial tilt

The axial tilt of Neptune is 28.32°. It is similar to the tilts of Earth 23° and Mars 25°. As a result, Neptune experiences similar seasonal changes to Earth but due to its long orbital period, the seasons last for 40 Earth years. Due to the fact that it lacks a solid body, its atmosphere undergoes differential rotations.

In the wide equatorial zone the rotation period is completed within 18 hours, much slower than the 16.11 - hour rotation of the planet's magnetic field.

The polar regions complete a rotation in 12 hours being the most pronounced differential rotation of any planet in the Solar System, resulting in strong latitudinal wind shear.

Orbital Resonances

Neptune's orbit has a profound impact on the region directly beyond it, known as the Kuiper belt. The Kuiper belt is a ring of small icy worlds, similar to the asteroid belt but far larger, extending from Neptune's orbit at 30 AU out to about 55 AU from the Sun. Many dwarf planets are located here.

Jupiter's gravity dominates the asteroid belt, shaping its structure and dominating the Kuiper Belt. Many regions in the Kuiper belt became destabilized due to Jupiter's gravity, creating gaps in the belt's structure. This can be observed in the 40 - 42 AU region. The most heavily populated resonance in the Kuiper belt, with over 200 known objects, is the 2:3 resonance.

Objects in this resonance complete 2 orbits for every 3 of Neptune, and are known as plutinos because the largest of the known Kuiper belt objects, Pluto, is among them. Although Pluto crosses Neptune's orbit regularly, the 2:3 resonance ensures they can never collide. The 3:4, 3:5, 4:7 and 2:5 resonances are less populated.

Structure

The internal structure is very similar to that of the planet Uranus. Its atmospheres forms about 5% to 10% of its mass and extends about 10% to 20% of the way towards the core reaching pressures of about 10 GPa or 100.000 times that of Earth's atmosphere. Concentrations of methane, ammonia and water are found in the lower regions of the atmosphere with the mantle equivalent to 10-15 Earth masses.

This mixture is referred to as "icy" even though it is a hot, dense fluid sometimes called a water-ammonia ocean. Going even deeper the conditions may be such that even methane decomposes into diamond crystals that rain downwards like hailstones. It is thought that this kind of diamond rain occurs also on Jupiter, Saturn and Uranus. The core is likely composed of iron, nickel and silicates. The core is estimated to be about 1.5 times the mass of Earth. The pressure at the center is 7 Mbar or 700 Gpa, twice as high as that at the center of Earth with temperatures of around 5.400 K.

Atmosphere and Climate

The atmosphere is made up mostly of hydrogen, helium and methane. Very similar to Uranus, its vivid blue color is influenced by the presence of methane and some unknown factor causes the more intense color. Neptune may not be as cold as Uranus but it has the most powerful winds out of all the planets in the Solar System despite being the furthest planet from the Sun and receiving the lowest energy input from it. Having the wildest and strangest weather in the entire Solar System, it is not understood how it gets this much energy in order to produce such weather.

Neptune has an average temperature of -214 degrees Celsius;-353 degrees. Wind speeds blowing westward on the equator reach up to 2,160 kilometers or 1.324 miles per hour, nearly a supersonic flow. Most winds travel retrograde to the rotation of the planet they are 5 times stronger than the strongest winds recorded on Earth, breaking the sound barrier. Bands and colossal storms also form on the planet.

In 1989 when Voyager 2 observed the planet, a Great Dark Spot was present among other spots. It was a storm about the size of Earth passing through Neptune's atmosphere. When Hubble was launched, astronomers wanted to see if these spots were a permanent feature like Jupiter's Great Red Spot but the storms were no longer there. Further observations led to discovery of other storms, each appearing and disappearing. The more active weather on Neptune might be due, in part, to its higher internal heat compared to that of Uranus.

Magnetosphere

Neptune's magnetic field is offset 47° relative to its rotational axis. It is believed that this is caused by the magnetic field not being generated in the core but rather by an electrically conducting liquid mantle, or that the mantle deflects the magnetic field from the core which gives it a weird offset in relation to the rotational axis.

No planet in the solar system has a perfectly aligned magnetic field. Even Earth's magnetic north is different from where the North Pole is. However, only Uranus and Neptune have such a tilted magnetosphere. Auroras exist on Neptune but they are very faint due to particles not getting charged so much by the sun, and because of the direction of the magnetosphere, they are mainly type B aurora, or SAR arcs. SAR arcs are not around the poles, but rather around the mid latitudes of the planet.

Planetary Rings

A common feature of the gas giants are their ring systems, which Neptune also has. It is very faint due to its low denseness and extremely dark color, a reddish hue. Neptune has 5 ring systems named after the people involved in the discovery and research of Neptune. The innermost is the Galle Ring, which is faint and wide at 2.000 km or 1.242 miles. The second is the first bright ring, named Le Verrier, it is only 113 km wide or 70.2 mi.

The third is the Lassell Ring, a very faint band 4.000km or 2.485 mi across. On the edge of this ring is the Arago Ring, slightly brighter and less than 100 km or 62 mi wide.

The last known and outermost ring is named the Adams Ring. It is about 35 km or 21.7 mi wide but it is one of the brightest rings. It has a special feature. It is slightly inclined with bright arcs in it. The three main rings are narrow and extend up to 63.000 km or 39.146 mi from Neptune. The Le Verrier Ring, at 53.000 km or 32.932 mi, and the broader, fainter Galle Ring, at 42.000 km or 26.097 mi.

Moons

A total of 14 known moons surround Neptune. They have all been named after water deities in Greek mythology. The first moon discovered was Triton, just 17 days after Neptune itself was discovered. It is also the largest of the 14 moons. The 14 moons of Neptune can be divided into regular, irregular and unusual irregular moons.

Regular moons

Out of the 14 moons, only 7 are inner regular moons, meaning they orbit along Neptune's ecliptic with very circular orbits or orbits with very low eccentricity.

In order of their distance from Neptune: Naiad, Thalassa, Despina, Larissa, Hippocamp and Proteus.

The smallest is Hippocamp 35km or 21.7 mi followed by Naiad 58 km or 36 mi, Thalassa 80 km or 49.7 mi, Despina 148 km or 91.9 mi, Galatea 158 km or 98.1 mi, Larissa 196 km or 121.7 mi and the second largest moon Proteus 438 km or 272 mi.

Naiad is the closest regular moon and the second smallest of the inner moons.

All of these regular moons have an average temperature between -221 degrees Celsius up to -224 degrees Celsius.

Irregular moons

The rest of the 14 Neptunian moons are irregular moons. Irregular moons follow an inclined, eccentric and often retrograde orbit.

In order of their distance: Triton, Nereid, Halimede, Sao, Laomedeia, Psamanthe, and Neso.

The smallest of the irregular moons is Psamanthe with a diameter of 40 km or 24.8 mi followed up by Laomedeia 42 km or 26 mi, Sao 44 km or 27.3 mi, Neso 60 km or 37.2 mi, Halimede 62 km or 38.5 mi, Nereid 340 km or 211 mi and the biggest of the moons Triton 2.706 km or 1.681.

All of these irregular moons have an average temperature between - 222 degrees Celsius up to -233 degrees Celsius.

Unusual Irregular Moons

Nereid is the third largest of the Neptunian moons, both it and Triton the largest moon - are considered unusual irregular moons and are two of the largest irregular moons known in the solar system. They both have atypically small semi-major axes and unusual orbital eccentricities

Nereid has one of the most eccentric orbits of any known irregular satellite, and Triton's orbit is a nearly perfect circle. Nereid also has the lowest inclination of any known irregular satellite.

Triton

Triton orbits clockwise around Neptune as Neptune rotates counterclockwise. Triton orbits at a 130 degree angle to the ecliptic of the planet though its orbital eccentricity is close to zero, being almost perfectly circular. The biggest moons in the solar system are usually regular moons, making Triton a bit special. Tritons size is even bigger than Pluto's a dwarf planet. It is strongly believed that Triton is actually a captured dwarf planet. It comprises 99.5% the mass found in Neptune's orbit.

It is the seventh largest moon in the solar system. Although Triton is now a captured object of Neptune's gravity, it is considered the biggest and most massive Kuiper Belt Object. Triton and Pluto share a identical composition, which supports the idea that they share a common origin.

Both Pluto and Triton have nitrogen ice surface, with other ices mixed in like water and carbon dioxide. It has a flat terrain with its topography never varying more than a kilometer. Ridges, plateaus and ice plains are present.

The small amounts of craters imply that its surface is very young and constantly renewed. It also has reddish patches like Pluto which is thought to be methane ice that reacted to UV light from the Sun, producing what is known as tholins, an organic compound.

However, even if primordial elements needed for life are present, it is far too cold on its surface -235 degrees Celsius. It is thought that underneath Triton's surface there is a silicate mantle and metallic core, this could explain its relatively high density for a moon of 2 g/cm ³.

The radioactive decay from the core could be enough to heat and power convection in a subsurface ocean of water, similar to what is thought to be under the surfaces of Europa, Enceladus and some other large moons. Just as in the case of Europa and Enceladus, cryovolcanism is an active process on Triton.

Liquid water in the mantle erupts onto the surface like lave on Earth thus the main reason why Triton's surface appears so young. It is actively renewed by liquid water erupting and then freezing on the surface.

If these eruptions are the reason why minerals, the source of the tholins and organic matter are present on the surface, then it means that organic compounds are found in the subsurface ocean thus creating a possibility for life to have been able to form there.

Life Habitability

Since it doesn't have a true surface but rather swirling fluids it is not conducive to life as we know it. Neptune's moon Triton however, appears more likely to develop life.

Future plans for Neptune

With new technologies coming up, Neptune is definitely a target for future studies by the use of new telescopes. Planned missions for Neptune are pretty vague since it would take well over 10 years to get there since it is the farthest planet.

Did you know?

- The name Neptune was first given to the seventh discovered planet of the Solar System, Uranus. However, the name was discarded but Uranus ultimately led to the discovery of the eight planet, that would bear the name Neptune.

- Uranus is Neptune's near twin in size and composition.

- In 2011 Neptune completed its first 165-year orbit since its discovery in 1846, meaning we have witnessed just 1 Neptunian year.

- Between 2013 - 2049, the closest approach of Neptune to Earth will happen in 2041 at a distance of 28.8 AU.

- Because of the dwarf planet Pluto's elliptical orbit, Pluto is sometimes closer to the Sun and Earth than Neptune is.

- Neptune is 30 times farther than Earth's orbit from the sun.

- The Sun is 900 times dimmer on Neptune than on Earth.

- Most languages use some variant of the name "Neptune" for the planet. In Chinese, Vietnamese, Japanese and Korean, the planet's name was translated as "sea king star" while in Mongolian it is called Dalain Van. In modern Greek the name is Poseidon while in Māori the planet is called Tangaroa, the name of the Māori god of the sea.

- Neptune has gravity at 1 bar of 11.15 m/s ², 1.14 times the surface gravity of Earth, and surpassed only by Jupiter who has a gravity of 24.79 m/s².

- A total of 58 Earths can fit in Neptune.

- The Voyager 2 is the only spacecraft to have reached Neptune to this day.

- Neptune has a very strong magnetic field.It is around 27 times stronger than the one on Earth.

[1.] Wikipedia

[1.] https://en.wikipedia.org/wiki/File:Neptune_-_Voyager_2_(29347980845)_flatten_crop.jpg

[2.] https://en.wikipedia.org/wiki/File:Neptune,_Earth_size_comparison_2b.jpg

[3.] https://en.wikipedia.org/wiki/File:Neptune_Orbit.gif

[4.] https://en.wikipedia.org/wiki/File:TheKuiperBelt_classes-en.svg

[5.] https://en.wikipedia.org/wiki/File:Neptune_clouds.jpg

[6.] https://en.wikipedia.org/wiki/File:Neptune%27s_Great_Dark_Spot.jpg

[7.] https://upload.wikimedia.org/wikipedia/commons/8/87/Neptunerings.jpg

[8.] https://upload.wikimedia.org/wikipedia/commons/a/a0/Neptunian_rings_scheme_2.svg

[9.] https://en.wikipedia.org/wiki/File:TheIrregulars_NEPTUNE.svg

[10.] https://en.wikipedia.org/wiki/File:Triton_moon_mosaic_Voyager_2_(large).jpg

[11.] https://en.wikipedia.org/wiki/File:Triton_(moon).jpg

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Neptune Facts | Temperature, Surface, Information, History & Definition

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Neptune is the fourth largest and the farthest planet of the Solar System with the most powerful wind speeds out of all the planets. It is the smallest of the gas giants and is the first planet to be discovered by mathematical predictions in 1846.

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Come on...pronounce it correctly. "YOOR a nus".

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Uranus is the seventh planet discovered in the Solar System that also led to the discovery of the last planet, Neptune they are both referred to as ice giants. Officially recognized in 1781 after many observations in the past, it is the third-largest planet of the Solar System.

Key Facts & Summary

Since ancient times it was not recognized due to its dimness and slow orbit. However, in 1781 Sir William Herschel announced its discovery being the first planet discovered with the help of a telescope.

It was given the name Uranus, after the Greek god of the sky Ouranos.

It is the only planet whose name is derived directly from a figure of Greek mythology.

The mean apparent magnitude of Uranus is 5.68 with a standard deviation of 0.17, making it near the limit of naked eye visibility.

Uranus is the seventh planet from the Sun, around 1.8 billion miles or 2.9 billion kilometers distance away.

It has the third-largest planetary radius and fourth-largest mass in the Solar System.

It has a radius of 25.362 kilometers or 15.759 miles, and has about 14.5 times the mass of Earth and four times its diameter - about 51.118 kilometers or 31.763 miles.

It is on an average distance of 19.2 AU away from the Sun and currently 18.8 AU away from Earth. Its actual distance can be checked online as Uranus is constantly tracked.

Its volume is about 63 times greater than Earth's, which means that 63 Earths can fit inside it.

The gravity on Uranus is about 8.87 m/s² or around 86% of the surface gravity on Earth which is 9.807 m/s².

It orbits the sun quite unusually, being the only planet whose equator is nearly at a right angle to its orbit, with a tilt of 97.77 degrees. Because of this, it rotates in the opposite direction than most planets, from East to West. Venus also does this but Uranus is the only known planet to rotate on its side.

It takes Uranus 84 years to complete an orbit of the Sun, the longest from all the planets in the solar system.

It also has the shortest day. One rotation on Uranus takes about 17 hours.

Uranus has the coldest planetary atmosphere in the solar system, -224 degrees Celsius;-371 degrees Fahrenheit.

Uranus and Neptune share similar composition, both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn. Because of this Uranus and Neptune are classified as ice giants rather than gas giants, for easier distinction.

Uranus has a similar atmosphere to Jupiter and Saturn in its primary composition of hydrogen and helium yet, it contains more "ices" such as water, ammonia, methane and traces of other hydrocarbons.

Though it appears featureless, without the cloud bands or storms associated with the other giant planets, it does have complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds.

Through analysis, the interior of Uranus has been stated to be made up primarily of ices and rock.

Uranus has 13 known rings around it. The innermost rings are narrow and dark, and its outermost rings are brightly colored.

Like the other gas giants, it also has a magnetosphere and many moons. Until now, 27 moons have been discovered orbiting Uranus. They were named after characters from the works of William Shakespeare and Alexander Pope.

Uranus has been visited only once by a spacecraft: Voyager 2.

Though it is visible to the naked eye, Uranus escaped clear classification for decades. Generally mistaken for a star, it is speculated that Hipparchos might have recorded it first in 128 BC in his star catalogue. Later it was incorporated into Ptolemy's Almagest.

However, the earliest definite sighting was in 1690. John Flamsteed observed it six times, cataloguing it as 34 Tauri. Later it was observed for about fourteen-times by Charles Le Monnier between 1750 and 1769. The man who finally solved this elusive object was William Herschel who observed it on 13 March 1781 with a telescope.

Although he first classified it as a comet, soon after reporting his discovery to other famous astronomers, it was concluded that in fact it was a planet. By 1783, Herschel acknowledged this and later was rewarded by the then king of England George III, on the condition that he moved to Windsor, in order for the royal family to also see it.

However, another problem was raised now, the name. It took about 70 years after the planet was discovered for astronomers to arrive at a consensus. Initially Herschel wanted to honor the king and name the new planet Georgium Sidus or "Georgian Planet." This decision was not popular outside Britain, and alternatives were proposed such as Herschel's own name, to even that of Neptune who wasn't by this time discovered. Neptune was quite popular since it would have honored the British Royal Naval victories in the course of the American Revolutionary War, but it was soon dropped.

In 1782 Johann Bode proposed the name Uranus, the Latinized version of the Greek god of the sky, Ouranos. His argument was that the new planet would stand out from the others if it wasn't following the mythology. Just as Saturn was the father of Jupiter, the new planet should be named after the father of Saturn. In 1789, an acquaintance of Bode, Martin Klaproth named his newly discovered element uranium in support of Bode's choice. The name became universal in 1850.

In other languages such as Chinese, Japanese, Korean and Vietnamese, Uranus is translated as "sky king star." Its official name in Thai is Dao Yurenat, in Mongolian Tengeriin Van meaning "King of the Sky" but in Hawaiian its name is Hele'ekala, a loanword for the discoverer of Uranus, Herschel.

Formation

Through simulations after the Nice model, it has been suggested that both Uranus and Neptune formed closer to the sun and later drifted away. It is hypothesized that the Solar System formed from a giant rotating ball of gas and dust known as the pre-solar nebula. Much of it formed the Sun while more of its dust went on and merged to create the first proto-planets. As they grew, some accreted enough matter for their gravity to hold unto the nebula's leftover gas. Estimates suggest the creation to have taken place about 4.5 billion years ago, and the drifting about 4 billion.

Distance, Size and Mass

Since its discovery, the planet has shifted it 1° west every 72 years however, its average distance from the sun still remains about 20 AU or 2 billion kilometers - 2 billion miles. The difference between its furthest and closest point from the sun is about 1.8 AU, larger than that of any other planet with the exception of the dwarf planet Pluto.

Though its mass is roughly 14.5 times that of Earth, it is the least massive compared to the other giant planets, having a mass of 8.681 × 10^25 kg. However, its diameter is slightly larger than that of Neptune, and it's about four times that of Earth: about 51.118 kilometers or 31.763 miles.

The density of Uranus 1.27 g/cm ³ makes it the second least dense planet, after Saturn. This value indicates that it is made primarily of various ices such as water, ammonia, and methane. The mass of its interior is however debatable, it is speculated to be around 9.3 and 13.5 Earth masses.

It has the third largest planetary radius: 25.362 kilometers or 15.759 miles, and its volume is about 63 times greater than Earth's, which means that 63 Earths can fit inside it.

Orbit and Rotation

It takes Uranus about 7 years to pass through each zodiac constellation, and a total of 84 years to make a complete trip around the sun. Its interesting orbing caught the attention of astronomers because the planet escaped its predicted location, and thus it led to the discovery of the last planet in 1846 that would later be called Neptune.

The interior rotation of Uranus is completed in about 17 hours, 14 minutes, and as in the case of all the gas giants its upper atmosphere experiences strong winds in the direction of rotation thus making a full rotation faster, in about 14 hours.

Axial tilt

The axis of rotation is approximately parallel with the plane of the Solar System, with a tilt of 97.77°. This feature gives Uranus completely different seasonal changes unlike those of other planets.

Near the solstice, one pole faces the sun continuously while the other is covered in complete darkness. At the other side of Uranus's orbit the orientation of the poles towards the Sun is reversed with each pole getting around 42 years of continuous light, and the other of darkness. Neat the time of the equinoxes, the Sun faces the equator of Uranus giving a period of day-night cycles similar to those seen on most of the other planets.

Uranus is hotter at its equator than at its poles. We do not know why this is so, nor do we know exactly why Uranus has such an unusual axial tilt. However, speculations suggest that Uranus suffered about 3 to 4 billion years ago, a collision with an Earth-sized protoplanet while the solar system was forming.

Structure

The standard model structure of Uranus consists of three layers: a rocky silicate/iron-nickel core in the center, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope.

The core's mass is estimated to be about 0.55% Earth masses with a radius less than 20% of the whole of Uranus. The mantle comprises its bulk, with around 13.4 Earth masses. The upper atmosphere is relatively insubstantial, weighing about 0.5 Earth masses and expanding for the last 20% of Uranus's radius. The core density is around 9 g/cm ³, with a pressure in the middle of about 8 million bars, and a temperature of about 5.000 K. What is referred to as the ice mantle is not in fact composed of ice in the conventional sense, but of a hot and dense fluid consisting of water, ammonia and other volatiles.

It is believed that the extreme temperatures and pressure condense carbon atoms into crystals of diamond. It is thought that these rainfalls of solid diamonds also occur on Jupiter, Saturn and Neptune. The prime factor that justifies the difference between Uranus and Neptune to Saturn and Jupiter is the fact that ice dominates over gases, hence the separate classification as "ice giants". Ice giants are believed to have liquid oceans and gas giants about 85% just gas.

Uranus has no solid surface because of its fluid interior structure. The atmosphere comprised of gases gradually transitions into the internal liquid layers. But for easier understanding, a revolving oblate spheroid set at the point at which atmospheric pressure equals 1 bar is conditionally designated as a "surface".

Though it is the coldest planet in the solar system, it is not know why. Something prevents the heat of Uranus's core from reaching the surface. It is believed that a form of barrier exists in the planets upper layers that stop the heat. Another theory suggests that after a massive collision, Uranus expelled most of its primordial heat, leaving its core temperature depleted.

Atmosphere

Uranus lacks a well-defined solid surface in its interior. However, the outermost part of the planet enveloped by gasses that is accessible to remote sensing is called its atmosphere. Remote-sensing capability extends down to roughly 300 kilometers or 186 miles below the 1 bar level, with a corresponding pressure of 100 bars and a temperature of 320 K (47 °C; 116 °F). Its atmosphere is mostly consistent in molecular hydrogen, helium, methane, ammonia, water, hydrogen sulfide, various hydrocarbons and water vapor, carbon monoxide and carbon dioxide possibly due to an external source such as in falling dust and comets.

Uranus has no mesosphere, but its atmosphere can be divided into three layers:

* Troposphere, between altitudes of -300 and 50 km (-186 and 31 mi), with pressures from 100 to 0.1 bar. It is the lowest and densest part of the atmosphere, the temperature decreases with altitude. It falls from approximately 320 K (47 °C; 116 °F) at the base of the nominal troposphere at −300 km or 186 miles to 53 K (−220 °C; −364 °F) at 50 km or 31 miles. The troposphere is thought to have highly complex cloud structures and is a dynamic part of the atmosphere, exhibiting strong winds, bright clouds and seasonal changes.

* Stratosphere, spanning altitudes between 50 and 4,000 km (31 and 2,485 mi), with pressures between 0.1 and 10 −10 bar. Temperatures gradually increase with altitude from 53 K (−220 °C; −364 °F) in the boundary of the troposphere to between 800 and 850 K (527 and 577 °C; 980 and 1,070 °F) at the base of the thermosphere. The heating is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons.

* Thermosphere, extending from 4,000 km to 50,000 km (2,485 and 31,068 mi). It's the outermost layer of the atmosphere and corona, with a uniform temperature around 800 to 850 K.

Magnetosphere

The magnetic field of Uranus is peculiar, it does not originate from its geometric center, and it is tilted at 59° from the axis of rotation. The magnetic pole is shifted from the center towards the south rotational pole by as much as one third of the planetary radius.

This asymmetric magnetosphere results in a magnetic field strength on the surface in the southern hemisphere of about 0.1 gauss or 10 µT, while in the northern hemisphere it can be as high as 1.1 gauss or 110 µT. The average field at the "surface" is 0.23 gauss or 23 µT. Studies of the date from the spacecraft Voyager 2, suggest that the asymmetry causes Uranus's magnetosphere to connect with the solar wind once a Uranian day, opening the planet to the Sun's particles.

The dipole moment of Uranus is 50 times that of Earth. It is believed that this is a common feature of ice giants since Neptune also has a similarly displaced and tilted magnetic field.

A possible explanation of this peculiar magnetosphere alignment may be due to Uranus's oceans of liquid diamond in the interior that would deter the magnetic field. Regardless, the other aspects of the magnetosphere are similar to other planets but overall, the structure is different from that of Jupiter and more similar to that of Saturn.

The aurorae of Uranus are relatively well developed. They are seen as bright arcs around both magnetic poles but they seem insignificant given the energy balance of the planetary thermosphere.

Climate

Uranus's atmosphere appears quite bland in comparison to the other giant planets, especially to Neptune whom it otherwise closely resembles.

A total of 10 cloud features were observed on the entire planet by the Voyager 2 spacecraft when it flew by Uranus in 1986. One explanation for this great lack of features is that the internal heat appears markedly lower than that of the other giant planets.

But all of this changed when the Hubble Space Telescope observed the ice giant. Analysis revealed that the planet had a dynamic weather, characterized by storms half as big as the United States or even twice in size.

In 2006 a dark cloud was spotted on the planet. This storm was gigantic, two thirds the size of the United States. The average temperatures of the clouds were -315 degrees Fahrenheit. The wind speeds can reach up to 560 miles or 900 kilometers per hour blowing in the retrograde at the equator, in the reverse direction of the planet's rotation.

Moons

Like other giant planets Uranus has many moons. Until now 27 satellites have been discovered, and were named after characters from the works of Shakespeare and Alexander Pope. Although the Uranian satellite system is the least massive among those of the giant planets. There are five main satellites that stand out: Miranda, Ariel, Umbriel, Titania and Oberon.

However they are small, even with the combined masses of all five they would still be less than half of Triton - the largest moon of Neptune. Every single one of them has a smaller surface area than the continent of Australia and most of them lack atmosphere.

Miranda

Miranda is a spherical moon and one of the strangest places in the solar system. It has a similar surface area to Chile: 700.000 km 2 while Chile has 750.000 km ². The landscape is very deformed with strange and hard to explain patterns occurring throughout the whole surface.

It is the smallest and innermost satellite of Uranus. It was discovered in 1948 and named after Miranda from Shakespeare's play The Tempest. It has a diameter of 470 kilometers or 292 miles, and it's one of the smallest yet closely observed objects in the Solar System.

It shares Uranus's extreme seasonal cycle for Miranda's orbit is perpendicular to the ecliptic. Its highest cliff named Verona Rupes, is a 20 kilometer-high scarp that is the highest cliff in the solar system. Canyons and mountains are also a common feature of Miranda which is peculiar since there is no geological activity.

Miranda and Uranus are 130.000 kilometers or 80.700 miles away from each other, three times closer than the moon is to Earth. Miranda has a low density of 1.2 g/cm 3 it is the least dense satellite of the five. This suggests that it is made up of 60% water-ice. It is thought that in the past the satellite was shattered by a giant object and the remaining pieces were pulled together by gravity thus forming it as it is now.

Ariel

It is the fourth largest of the known moons of Uranus, the second smallest after Miranda, and it orbits and rotates in the equatorial plane of its parent planet. This is almost perpendicular to the orbit of Uranus thus resulting in extreme seasonal cycles. It has an estimated diameter of 1,157 kilometers or 718 miles.

Discovered in 1851 by William Lassell and named after two characters: the sky spirit in Alexander Pope's The Rape of the Lock and the spirit who serves Prospero in Shakespeare's The Tempest.

It ranks 14 th among the 19 smallest known spherical moons in the Solar System. It is estimated to be composed out of equal parts of rock and ice. It shows more geological activity than the other moons most likely due to tidal heating. It is also believed to have formed from an accretion disc that surrounded the planet shortly after its formation. Its inner core is comprised of rock surrounded by an ice mantle. Its mass is equivalent in magnitude to Earth's hydrosphere. It is the second closest to Uranus, orbiting at the distance of about 190.000 kilometers or 118.060 miles.

It completes an orbit in 2.5 days with one side always facing the planet. Its orbit lies completely in Uranus's magnetosphere this bombardment may lead to the darkening of the trailing hemispheres observed for all Uranian moons. It may have the third largest mass with a density of 1.66 g/cm ³.

Umbriel

Also discovered by William Lassell in 1851, the moon consists mainly of ice and only a fraction of rock. It has the darkest surface of the Uranian moons and appears to have been shaped by impacts.

It is the second most heavily cratered Uranian moon after Oberon, with craters reaching up to 210 kilometers or 130 miles. A prominent surface feature is a ring of bright material on the floor of the Wunda crater. This moon was named after the dusky melancholy sprite in Alexander Pope's The Rape of the Lock.

The name suggests the Latin word umbra, meaning shadow. It is the third farthest moon orbiting the planet at a distance of 266.000 kilometers or 165.000 miles. Its orbital period is the same as its rotational period, 4.1 Earth days. This means that Umbriel also has one side always facing Uranus. Its orbit is also captured in Uranus's magnetosphere. It has a density of 1.39 g/cm ³ and it reflects less than half as much light as Ariel. It has an estimated diameter of 1,169 kilometers or 726 miles.

Titania

The largest moon of Uranus, and the eight largest moon in the Solar System with a diameter of 1,578 kilometers or 981 miles. It was discovered in 1787 by William Herschel, the discoverer of Uranus. It was named after the queen of the fairies in Shakespeare's - A Midsummer Night's Dream.

It has about half the radius of Earth's moon about 788.9 kilometers or 490 miles. In 2005 infrared spectroscopy revealed the presence of water ice as well as frozen carbon dioxide on its surface. It has a density of 1.71 g/cm³ that indicates an equal consistency of water ice and dense non-ice components. It is the most massive of the Uranian moons, and the 8 th most massive moon in the Solar System.

Like the three aforementioned moons its orbit is also caught in Uranus's magnetosphere. It orbits Uranus at a distance of approximately 436,000 kilometers or 271,000 miles being the second farthest from the planet among the other four moons.

An orbital period is completed in 8.7 days. It is also tidally locked satellite, having just one side of it permanently facing Uranus. Its surface is cut by a system of enormous canyons, scarps and it appears a bit reddish. Numerous impact craters can reach up to 326 kilometers or 203 miles in diameter but it is less heavily cratered than Oberon.

Oberon

Oberon is the outermost major moon of Uranus. It was discovered in 1787 by William Herschel who also discovered Titania. It is the second-largest and second most massive of the five major Uranian moons.

Also the ninth most massive moon in the Solar System, Oberon was named after the mythical king of the fairies in Shakespeare's - A Midsummer Night's Dream.

While the other moons orbit inside Uranus's magnetosphere, Oberon's orbit lies partially outside. Its surface is dark and a bit red in color, covered by asteroid and comet impacts with craters reaching up to 210 kilometers or 130 miles in diameter.

Oberon can be seen from Earth with a relatively good amateur telescope. It orbits around Uranus at a distance of about 584.000 kilometers or 362.880 miles being the furthest moon, and completing a cycle in about 13.5 days. Like the other Uranian moons it also has one side permanently facing its parent planet.

The difference between it and the other planets is that Oberon spends the majority of its orbit outside Uranus's magnetosphere, and as a result it is directly hit by solar wind. Once every 42 years during Uranus's equinox, and its equatorial plane intersects with Earth, mutual occultation occurs between the Uranian moons.

Oberon has a density of 1.63 g/cm³. This is higher than the typical density of Saturn's satellites. Titania also has this characteristic. Spectroscopic observations have revealed the presence of crystalline water ice on the surface. It is speculated that Oberon may possess a liquid ocean layer at the core-mantle boundary. Oberon is the most reddish Uranian moon, and the most heavily cratered implying that it has the oldest surface among the satellites.

Planetary Rings

Uranus has thirteen distinct ring systems thought to have formed about 600 million years ago from the collision of possible other moons or big objects. The rings around Uranus are unique since they aren't bright like the ones of Saturn. With this low albedo they appear dark as charcoal and another unique feature is that they are extremely narrow. The widest of the rings is called the epsilon ring, spreading from 20 to 100 kilometers wide.

In 1978, nine distinct rings were discovered, two more in 1986 and by 2003-2005 an additional two. Most of them are opaque and consist of large bodies 0.2 - 20m in diameter made up of water ice with the addition of some dark radiation-processed organics. Their radii range extends from about 38.000 kilometers to 98.000 or 23.612 to 60.894 miles.

Life Habitability

Since it doesn't have a true surface but rather swirling fluids it is not conducive to life as we know it.

Future plans for Uranus

With new technologies coming up, Uranus is definitely a target for future studies and some missions have already been announced though it remains to be seen if they will take place.

Did you know?

In 2033, Uranus will complete its third orbit around the sun since its discovery in 1781. The planet returned to the point of its discovery twice since then, in 1862 and 1943, one day later each time.

Because of its brightness, the planet can be seen in urban conditions on a good night, even without binoculars.

Though it is 20 times further away from the Sun than Earth, Uranus's intensity of light is about 1/400 that of Earth.

Uranus is Neptune's near twin in size and composition.

The third most abundant component of Uranus's atmosphere is methane. Methane has prominent absorption bands in the visible and near-infrared, making Uranus aquamarine or cyan in color.

Between 2013 - 2100, the closest approach of Uranus to Earth will happen in 2051 at a distance of 17.2 AU.

1. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranus2.jpg

2. https://upload.wikimedia.org/wikipedia/commons/9/95/Uranus%2C_Earth_size_comparison_2.jpg

3. https://en.es-static.us/upl/2015/01/uranus-seasons-orbit-lg-e1485185411910.jpg

4. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranus_orientation_1985-2030.gif

5. https://upload.wikimedia.org/wikipedia/commons/f/fe/Uranus-intern-en.png

6. https://en.wikipedia.org/wiki/Uranus#/media/File:Adding_to_Uranus's_legacy.tif

7. https://en.wikipedia.org/wiki/Uranus#/media/File:Tropospheric_profile_Uranus_new.svg

8. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranian_Magnetic_field.gif

9. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranuslight.jpg

10. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranuscolour.png

11. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranus_clouds.jpg

12. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranus_Dark_spot.jpg

13. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranian_moon_montage.jpg

14. https://en.wikipedia.org/wiki/Miranda_(moon)#/media/File:PIA18185_Miranda's_Icy_Face.jpg

15. https://en.wikipedia.org/wiki/Miranda_(moon)#/media/File:Miranda_scarp.jpg

16. https://en.wikipedia.org/wiki/Ariel_(moon)#/media/File:Ariel_(moon).jpg

17. https://en.wikipedia.org/wiki/Umbriel_(moon)#/media/File:Umbriel_usgsx2.jpg

18. https://en.wikipedia.org/wiki/Titania_(moon)#/media/File:Titania_(moon)_labeled.jpg

19. https://en.wikipedia.org/wiki/Oberon_(moon)#/media/File:Oberon-NASA_names_en.png

20. https://en.wikipedia.org/wiki/Uranus#/media/File:Uranian_rings_scheme.png

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Uranus Facts | Rotation, Rings, Atmosphere, Size, History & Definition

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Uranus is the seventh planet discovered in the Solar System that also led to the discovery of the last planet, Neptune they are both referred to as ice giants. Officially recognized in 1781 after many observations in the past, it is the third-largest planet of the Solar System.

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Known by its visible rings - Saturn.

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Saturn - Educational facts and history of the planet Saturn.

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In Roman mythology, Saturn is the god of agriculture. The associated Greek god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter). Saturn is the root of the English word "Saturday"

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The first of the outer planets - Jupiter.

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Jupiter - Educational facts and history of the planet Jupiter.

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Jupiter is the fifth planet from the Sun and by far the largest.Jupiter is more than twice as massive as all the other planets combined (the mass of Jupiter is 318 times that of Earth).

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The red planet - read all about Mars.

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Due to its brightness and closeness to Earth, Mars has been documented for at least 4.000 years thus it is impossible to credit someone with its discovery. However, the first person to observe Mars with a telescope was Galileo Galilei in 1610.

It is named after the Roman god of war due to its red appearance. In different cultures, Mars represents masculinity, youth and its symbol is used as the symbol for the male gender.

Due to the effects of the iron oxide prevalent on Mars's surface, it has a reddish appearance distinctive among the astronomical bodies visible to the naked eye.

It is a terrestrial planet with a thin atmosphere, having surface features reminiscent of both the impact craters of Earth's Moon, and the valleys, deserts and polar ice caps of Earth.

Mars is 227.9 million km / 141.6 million mi or 1.5 AU away from the Sun. It takes sunlight about 13 minutes to reach Mars.

The farthest distance from Earth is 401 million km / 249 million mi, and its closest distance to us can be 54.6 million km / 34 million mi, while the average distance is 225 million km / 140 million mi.

Mars has a radius of 3.389 km or 2.105 mi being twice as small as Earth.

The diameter of Mars is 6.779 km or 4.212 mi, slightly more than half the size of Earth.

Mars's mass is 6.42 x 10²³ kilograms, about 10 times less than Earth.

Mars has a volume of 1.6318 x 10¹¹ km³ (163 billion cubic kilometers) which is the equivalent of 0.151 Earths.

The gravity on Mars is about 38% of Earth's gravity.

Mars has a density of 3.93 g/cm³, lower than Earth's density, indicating that its core region contains lighter elements.

One rotation/day on Mars is completed within 24.6 hours while a whole trip around the Sun or year, is completed within 669.6 days.

Mars's axis of rotation is tilted 25.2 degrees similar to Earth which has an axial tilt of 23.4 degrees.

Mars has seasons though they last longer than on Earth since Mars takes longer to orbit the Sun. The seasons vary in length due to Mars's elliptical, egg-shaped orbit around the Sun.

Spring in the northern hemisphere (autumn in the southern) is the longest season lasting 194 days. Autumn in the northern hemisphere (spring in the southern) is the shortest at 142 days. Northern winter (southern summer) lasts 154 days while northern summer (southern winter) lasts 178 days.

On average, the temperature on Mars is about -80 degrees Fahrenheit / -60 degrees Celsius. In winter, near the poles temperatures can get down to -195 degrees F / -125 degrees C.

From time to time, winds on Mars are strong enough to create dust storms, covering most of the planet while taking months for all the dust to settle, a great impediment for space probes.

Its atmosphere is mostly composed of carbon dioxide, nitrogen and argon gases.

Mars has the tallest volcano/mountain in the entire Solar System, named Olympus Mons at a height of 13 miles / 21 kilometers and also the biggest canyon Valles Marines.

Mars has two moons named Phobos and Deimos. Interestingly Jonathan Swift wrote about these moons in his book "Gulliver's Travels" - what is strange is that these moons weren't even discovered in that period of time. They were discovered 151 years later after the book was written.

Mars does not have any rings but it is estimated that its moon Phobos will crash into Mars in about 50 million years, possibly creating a ring system afterwards.

Mars doesn't have a magnetic field but certain areas are highly magnetized, indicating traces of a magnetic field from 4 billion years ago.

It lacks an active plate tectonic system.

Through continuous observations and analysis, it is strongly believed that Mars was once very similar to Earth, possessing water or even whole oceans. Recent studies indicate that it may have water even now.

Mars has been observed by many different cultures from around the world since hundreds of years. Because of this it is impossible to credit anyone with its discovery, Mars being easily visible with the naked eye.

Observations date back to ancient Egyptian astronomers in the 2 nd millennium BCE while Chinese records about the motions of Mars appeared before the founding of the Zhou Dynasty in 1045 BCE.

Detailed observations were made even by the Babylonians who developed arithmetic techniques to predict the future position of the planet while the ancient Greeks developed a geocentric model to explain the planets motions.

To the ancient Romans, the planet Mars was symbolic of blood and war, the equivalent of the Greek god of war Aries. In the 16 th century, Nicolaus Copernicus proposed a heliocentric model for the Solar System in which the planets follow circular orbits around the Sun.

Johannes Kepler revised this creation, yielding an elliptic orbit for Mars that more accurately fitted the observational data. In 1610, Galileo Galilei first observed Mars with a telescope and within a century, astronomers discovered several features of Mars and determined the planet's rotational period and axial tilt.

The idea of life on Mars started a long time ago, and in a way this helped fuel the drive for searching it upon Mars. Since 1877 onward, it was mistakenly thought that water was found on Mars and later the idea of life became popularized among the public.

Percival Lowell believed he could see a network of canals on Mars but they were proved to be optical illusions. Since then, many more details about the planet were gathered both exciting and disappointing, and the presence of today's robots on the planet are a testament of the will of the people who wish to finally find a trace of life on Mars, even if it means finding evidence of past life.

Formation

It is hypothesized that the Solar System formed from a giant rotating ball of gas and dust known as the pre-solar nebula. Much of it formed the Sun while more of its dust went on and merged to create the first proto-planets. Mars was one of these planets and after the gravity pulled enough swirling gas and dust, it became the fourth planet from the Sun.

Distance, Size and Mass

Mars is about 227.9 million km / 141.6 million mi or 1.5 AU away from the Sun. It takes sunlight about 13 minutes to reach Mars. The diameter of Mars is 6.779 km or 4.212 mi, slightly more than half the size of Earth.

In a way, its diameter is about the width of the continent of Africa. Mars's mass is 6.42 x 10 ²³ kilograms, about 10 times less than Earth and a volume of 1.6318 x 10¹¹ km³ (163 billion cubic kilometers) which is the equivalent of 0.151 Earths. Its entire surface area is similar to that of all the Earth's continents combined

Orbit and Rotation

One rotation/day on Mars is completed within 24.6 hours while a whole trip around the Sun or year, is completed within 669.6 days.

Mars has a relatively pronounced orbital eccentricity of about 0.09. Of the seven other planets in the Solar System, only Mercury has a larger orbital eccentricity. It is known that in the past, Mars had a much more circular orbit. At one point, 1.35 million Earth years ago, Mars had an eccentricity of roughly 0.002, much less than that of Earth today.

It is believed that the closest distance between Earth and Mars will continue to mildly decrease for the next 25.000 years.

Axial tilt

Mars's axis of rotation is tilted 25.2 degrees similar to Earth which has an axial tilt of 23.4 degrees. It has seasons though they last longer than on Earth since Mars takes longer to orbit the Sun. The seasons vary in length due to Mars's elliptical, egg-shaped orbit around the Sun.

Structure

It is estimated that Mars has a dense core with a radius between 930-1.300 miles / 1.500 - 2.100 kilometers. It is made up primarily of iron and nickel with about 16-17% sulfur. The iron sulfide core is thought to be twice as rich in lighter elements then Earth's core.

The core is surrounded by a silicate mantle which formed many tectonic plates and volcanic features on the planet that now appear to be dormant.

Besides silicon and oxygen, the most abundant elements in Martian crust are iron, magnesium, aluminum, calcium and potassium, an average thickness of the planet's crust has been estimated to be about 50 km / 31 mi, with a maximum thickness of 125 km / 78 mi. In comparison, Earth's average crust is about 40 km / 25 mi.

Magnetosphere and Atmosphere

It is estimated that Mars lost its magnetosphere around 4 billion years ago. A possible reason for this is because of numerous asteroid strikes and the solar wind interacting directly with the Martian ionosphere, lowering the atmospheric density by stripping away atoms from the outer layer.

The atmosphere of Mars consists of about 96% carbon dioxide, 1.93% argon and 1.89% nitrogen, along with traces of oxygen and water. It is quite dusty. Recently methane has also been detected in the atmosphere, values of which indicate an active source of gas that should be present be it biological or non-biological.

Climate

If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its axial tilt is similar to Earth's. Spring in the northern hemisphere (autumn in the southern) is the longest season lasting 194 days. Autumn in the northern hemisphere (spring in the southern) is the shortest at 142 days. Northern winter (southern summer) lasts 154 days while northern summer (southern winter) lasts 178 days.

On average, the temperature on Mars is about -80 degrees Fahrenheit / -60 degrees Celsius. In winter, near the poles temperatures can get down to -195 degrees F / -125 degrees C. Mars has the largest dust storms in the Solar System, reaching speeds of over 160 km/h (100 mph). These can vary from a storm over a small area, to gigantic storms that cover the entire planet. They tend to occur when Mars is closest to the Sun, increasing global temperature.

Surface and Geology

Though it is often referred to as the Red Planet, Mars actually has many colors. At the surface colors such as brown, gold and tan are present. Its surface is the same size as Earth's dry lands combined, even though it is two times smaller.

Mars has many evidences of a watery past, with ancient river valley networks, deltas and lakebeds, as well as rocks and minerals on the surface that could only have formed in liquid water. Some features suggest that Mars experienced huge floods about 3.5 billion years ago.

Hydrology / Topography / Volcanoes

Though liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is less than 1% that of Earth's, except for short periods, the volume of water ice caps appear to be made largely out of water with a volume of water ice enough to cover, if melted, the entire planetary surface to a depth of 11 meters or 36 ft.

There are landforms visible that strongly suggest that liquid water has existed on the planet's surface like hematite concretions (image above), or the Ma'adim Vallis, a valley of about 700 km / 430 mi thought to have been carved by flowing water long ago.

Near the northern polar cap is the 81.4 km / 50.6 mi wide Korolev Crater, where it was found to be filled with about 2.200 cubic km / 530 mi of water ice.

There are two permanent polar ice caps on Mars. During winter, the pole's lay in continuous darkness and causing depositions of 25-30% of the atmosphere into slabs of carbon dioxide dry ice.

When they are exposed again to sunlight the carbon dioxide sublimates and sometimes create water-ice clouds. Both polar caps consist primarily of water ice, about 70%.

The dichotomy of Martian topography is striking, northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts.

Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of 5 km (3.1 mi) or greater have been found. The largest confirmed of these is the Hellas impact basin, a light albedo feature clearly visible from Earth.

The volcano Olympus Mons, is an extinct volcano in the vast upland region Tharsis, which contains several other large volcanoes. Olympus Mons is however the greatest, in fact it is the largest volcanoe detected in the entire Solar System, it has about three times the height of Mount Everest.

The large canyon, Valles Marineris also known as Agathadaemon in the old canal maps, has a length of 4,000 km (2,500 mi) and a depth of up to 7 km (4.3 mi). The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars. By comparison, the Grand Canyon is only 446 km (277 mi) long and nearly 2 km (1.2 mi) deep. Valles Marineris was formed due to the swelling of the Tharsis area, which caused the crust in the area of Valles Marineris to collapse.

It is 10 times longer and 10 times wider than the Grand Canyon. Mars also has sand on its surface, made up from basaltic rock, thus having a grey color.

When the wind blows, dunes are created including series of parallel ridges in crater floors, also horseshoe-shaped dunes are created. Mars also has dust devils, towering vortices of wind similar to tornadoes. When the dust devils blow the red dust around on the greyish basaltic plains, they can leave behind complex and beautiful curlicues.

Mars actually has avalanches. Cliffs towering above the surface that hold different materials can be dislodged in the spring when carbon dioxide thaws, creating tremendous cascades of rock and dust.

Moons

Mars has only 2 known moons named Phobos and Deimos after the horses that pulled the chariot of the god of war Mars. They are very small though, Phobos has a diameter of about 25 km or 15.5 mi, while Deimos just 15 km or 9.3 mi. They look very much like asteroids and it is strongly believed that they have been captured by Mars gravity from the nearby asteroid belt.

Phobos orbits Mars only 6.000 km or 3.728 mi over the surface, moving so rapidly in its orbit that it orbits faster than Mars rotates. Tides from Mars are also altering its orbit, slowly lowering Phobos closer and closer to the surface. It is believed that in a few million years Phobos will drop low enough that it will actually enter the atmosphere and impact the surface.

Life Habitability

On June 7, 2018, NASA announced that the Curiosity rover had discovered organic compounds in sedimentary rocks dating to three billion years old, indicating that some of the building blocks for life were present.

In July 2018, scientists reported the discovery of a sub-glacial lake on Mars, the first known stable body of water on the planet. It sits 1.5 km (0.9 mi) below the surface at the base of the southern polar ice cap and is about 20 km (12 mi) wide. Out of all the planets in the Solar System, Mars appears to have the highest change of having life forms but still the conditions are harsh enough that nothing should be able to survive there, perhaps only beneath the surface.

Still, regardless of its habitability now, Mars was definitely once a planet filled with oceans and the right conditions of life. Most people would be happy if we could only find evidence of life that may have existed on the Red Planet.

Future plans for Mars

Future astrobiology missions are planned, including the Mars 2020 and Rosalind Franklin rovers. They have the mission to take soil samples and return them to Earth for further analysis. If we look into Mars's history, it is one of the most actively observed planets in the Solar System and chances are it will remain so for a long time.

There are many plans for Mars, including terraforming and sending people on it, but it remains to be seen, hopes are high and missions continue.

Did you know?

- Mars is the most intensely studied planet with observations dating back to 4.000 years ago.

- It is about 50% farther from the Sun than Earth.

- Perhaps second only to Venus when it comes to "visits", Mars has been visited over 16 times over about 39 attempts with the first successful mission happening in 1965 with the Mariner 4 spacecraft flyby.

- If you weigh 100kg on Earth, on Mars your weight would be 38kg.

- Mars is the outermost terrestrial planet, outside Earth's orbit.

- Theoretically, Mars is populated by robots since we sent so many there.

- Mars has captured our imagination so much, that it has spanned countless adaptations on TV, literature and it may as well be the most popular planet after Earth.

- On Mars the Sun appears about half the size as it does on Earth.

- Pieces of Mars have fallen to Earth. Scientists have found tiny traces of Martian atmosphere within meteorites violently ejected from Mars, then orbiting the solar system amongst galactic debris for millions of years, before crash landing on Earth.

- A year on Mars is almost twice as long as a year on Earth.

- It would take more than six Mars to fill the volume of Earth.

- Almost 7 million Mars can fit in the Sun.

- The Mars One project hopes to colonize the Red Planet, beginning in 2022.

[1.] Wikipedia

[1.] https://upload.wikimedia.org/wikipedia/commons/0/02/OSIRIS_Mars_true_color.jpg

[2.] https://en.wikipedia.org/wiki/Heliocentrism#/media/File:Heliocentric.jpg

[3.] https://en.wikipedia.org/wiki/File:Mars,_Earth_size_comparison.jpg

[4.] https://en.wikipedia.org/wiki/File:Marsorbitsolarsystem.gif

[5.] https://sites.google.com/site/missiontomarsatvssec/home/mission-background-briefing-students/earth-vs-mars/structure-of-the-earth

[6.] https://en.wikipedia.org/wiki/File:USGS-MarsMap-sim3292-20140714-crop.png

[7.] https://en.wikipedia.org/wiki/File:Spirit_Mars_Silica_April_20_2007.jpg

[8.] https://en.wikipedia.org/wiki/File:Nasa_mars_opportunity_rock_water_150_eng_02mar04.jpg

[9.] https://en.wikipedia.org/wiki/Ma%27adim_Vallis

[10.] https://en.wikipedia.org/wiki/File:Perspective_view_of_Korolev_crater.jpg

[11.] https://en.wikipedia.org/wiki/File:Martian_north_polar_cap.jpg

[12.] https://en.wikipedia.org/wiki/File:PIA23304-Mars-ImpactCrater-Sep2016-Feb2019.jpg

[13.] https://en.wikipedia.org/wiki/File:Olympus_Mons_alt.jpg

[14.] https://en.wikipedia.org/wiki/Valles_Marineris#/media/File:Mars_Valles_Marineris.jpeg

[15.] https://www.theatlantic.com/science/archive/2016/05/mars-ice-age/484541/

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Mars Facts | Temperature, Surface, Information, History & Definition

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Due to its brightness and closeness to Earth, Mars has been documented for at least 4.000 years thus it is impossible to credit someone with its discovery. However, the first person to observe Mars with a telescope was Galileo Galilei in 1610. It is named after the Roman god of war due to its red appearance.

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I hope you know something about this planet - you live there!  Third rock from the sun - Earth.

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Earth is the third planet from the Sun and the fifth largest planet in the Solar System with the highest density. It is currently the only known location where life is present.

Key Facts & Summary

The realization that Earth is a planet, and a planet among many others was established "fairly" recently, in the 17th century - this realization came through by the combined forces of ancient philosophers, mathematicians, and astronomers.

Plato correctly deduced that the Earth is spherical but this idea would take root and be proven much later.

The name "Earth" - is at least 1.000 years old, and it is a Germanic word which simply translates to "the ground." It is not known who came up with it but it is the only planet that wasn't named after a Greek or Roman god.

However, the Greek equivalent to Earth is Gaia - terra mater - mother Earth, and Roman equivalent was Tellus - the fertile soil.

Earth is estimated to have formed around 4.5 billion years ago - almost one-third of the age of the universe - through accretion from the solar nebula.

Earth is the third planet from the Sun, at a distance of 1 AU or 147 million km / 91 million mi.

It is the fifth-largest planet in the Solar System, being the largest of the terrestrial planets.

It has an equatorial radius of 6.371 km / 3.958 mi, and a polar radius of 6.356 km / 3.949 mi, meaning it is not completely spherical but rather bulged at the equator due to rotation.

The Earth has a diameter of 12.742 km / 7.917 mi.

Earth has a mass of about 6.6 sextillion tons and a volume of about 260 billion cubic miles / 1 trillion cubic kilometers.

The surface area of Earth is about 197 million square miles / 510 million square kilometers.

Around 71% of the surface is covered by water and 29% by land.

The water is 3% fresh and 97% salted. Of that 3% freshwater, over 2% is frozen in ice sheets and glaciers meaning that less than 1% is freshwater found in lakes, rivers, and the underground.

In regards to land, the continent of Asia covers about 30% of all the land, having around 60% of the world's population.

The atmosphere of Earth is composed of roughly 78% nitrogen, 21% oxygen, 0.97% argon and carbon dioxide and about 0.04% other gases and water vapor. The mixture of gases is commonly known as air.

The thickness of the atmosphere is about 60 miles / 96 kilometers.

The atmosphere of Earth is divided into 6 layers: troposphere, stratosphere, mesosphere, thermosphere, exosphere, and ionosphere.

The highest temperatures on Earth can reach up to more than 110 degrees Fahrenheit / 48 degrees Celsius, and the lowest around -126 degrees Fahrenheit / -88 degrees Celsius, maybe even lower.

Earth has the greatest density out of all the planets in the solar system - 5.51 g/cm³ - and a gravity of 9.807 m/s² or 1 g.

This suggests that the Earth's core is solid, made of iron and nickel about 759 miles / 1.221 kilometers in radius. The temperatures at the core have been estimated to be around 9.800 degrees Fahrenheit / 5.400 degrees Celsius. This is hotter than the surface of the Sun.

Together with the inner core, Earth also has an outer core, with the crust being the mantle and the thickest layer. It is a viscous mixture of molten rock about 1.800 mi / 2.900 km thick and has the consistency of caramel.

The outermost layer - Earth's crust - goes about 19 mi / 30 km deep on average on land. But at the bottom of the ocean, the crust is thinner and extends about 3 mi / 5 km from the seafloor to the top of the mantle.

Earth has only one satellite - the Moon - and a couple of temporal artificial satellites.

Earth's axis is tilted 23.5 degrees from the plane of its orbit around the Sun. The tilt varies between 22.1 and 24.5 degrees, causing seasons and even chaotic seasons. It changes positions once every 40.000 years.

Earth completes a rotation/day - from West to Est - once every 23.9 hours. One orbit/year - a trip around the Sun - is completed within 365 days. The Earth's orbit is elliptical or oval-shaped.

Earth's magnetosphere acts as a shield against solar and cosmic particle radiation. It has the shape of a tear-drop reaching 36.000 mi / 57.936 km into space, and it is one of the reasons life has managed to develop.

Since ancient times the Earth was taught to be at the center of the Universe with the other celestial objects orbiting around it. Some believed that the Earth was flat, while the ancient Greeks such as Plato correctly deduced that the Earth was a sphere.

Soon after, the Greek astronomer Ptolemy proposed the idea that planets were in tiny spheres and made circles as they orbited Earth.

In the 16 th century, the Polish mathematician/astronomer Nicolaus Copernicus created the heliocentric model of the Solar System - where everything orbited the Sun.

Later, in the 17 th century, Galileo Galilei observed and discovered Jupiter and that it had moons of its own, and that Venus went through phases like the Moon.

Observations continued, ideas caught up and finally, it was established that Earth was a planet among many others. The name of our planet came from the Anglo-Saxon word "erda" and the Germanic word "erde" - they both mean soil or ground.

The old English version of these words became "eor(th)e" or "ertha", which later transformed into "Earth." Many other languages use some form of variation or naming of their own such as: Aarde, Terre, Tera, Jorden, Nchi, Bumi, and many more. We who inhabit Earth can be referred to as: Earthlings, Earthers, Terrans or Gaians.

Formation

The Earth is believed to have formed around 4.5 billion years ago. The duration for this formation has been estimated to have lasted about 10 to 20 million years.

The theory states that a solar nebula partitions a volume out of a molecular cloud by gravitational collapse which begins to spin and flatten into a circumstellar disk.

The planets grow out of that disk through gravity pulling swirling dust and gas. Slowly, the Earth's atmosphere and oceans were formed by volcanic activity and outgassing.

It is believed that water vapor condensed into the oceans being augmented by water and ice from asteroids, protoplanets, and comets.

The atmospheric greenhouse kept the oceans from freezing when the newly formed Sun had only 70% of its current luminosity. When the Earth's magnetic field was established it helped to prevent the atmosphere from being stripped away by the solar wind.

A crust formed when the molten outer layer of Earth cooled to form a solid. There are two models who propose that the landmass steadily grew to present-day forms, or, more likely that it grew rapidly early in Earth's history, followed by a long-term steady continental area. The continuous loss of heat from Earth's interior, helped continents form through - plate tectonics.

Through periods of hundreds of millions of years, the supercontinents have assembled and then broke apart. About 750 million years ago, the earliest known supercontinent Rodinia began to break apart.

The continents later rejoined and combined again to form Pannotia about 600 to 540 million years ago. This happened again and the supercontinent of Pangaea formed but also broke apart about 180 million years ago.

There are patterns that suggest that ice ages began about 40 million years ago and intensified during the Pleistocene around 3 million years ago. Many high-latitude regions have undergone repeated cycles of glaciation and thaw, repeating about every 40.000 to 100.000 years. It is believed that the last continental glaciation ended 10.000 years ago.

Distance, Size and Mass

Earth is the third planet from the Sun, at a distance of 1 AU or 147 million km / 91 million mi. It is situated in the goldilocks zone where temperatures are just right for liquid water to exist and for life to evolve.

Depending upon their current orbital positions, either Venus or Mercury are the closest planets to Earth. It has an equatorial radius of 6.371 km / 3.958 mi, and a polar radius of 6.356 km / 3.949 mi, meaning it is not completely spherical but rather bulged at the equator due to rotation.

The diameter of Earth is around 12.742 km / 7.917 mi being the fifth largest planet from the solar system, and the largest of the terrestrial planets ( Venus, Mercury, Mars).

The Earth is so big that if it were hallowed, almost 50 moons could fit inside it. Earth has a mass of about 6.6 sextillion tons and a volume of about 260 billion cubic miles / 1 trillion cubic kilometers. It has the biggest mass out of all the terrestrial planets and the greatest density out of all the planets - 5.51 g/cm³. Earth's mass composition is mostly comprised of iron 32.1%, oxygen 30.1%, silicon 15.1%, magnesium 13.9%, sulphur 2.9%, nickel 1.8 %, nickel 1.8%, calcium 1.5%, and aluminum 1.4%. The remaining 1.2% consists of trace amounts of other elements.

Orbit and Rotation

The Earth makes a complete rotation on its axis once every 23.9 hours. It takes Earth 265,25 days to complete one trip around the Sun - year. In order for calendars to maintain their consistency with this orbit, every 4 years one day is added - this is called a leap day - as well as a leap year.

Earth's orbital speed averages 29.78 km/s (107,208 km/h; 66,616 mph), which is fast enough to cover the planet's diameter in 7 minutes and the distance to the Moon in 4 hours.

Structure - Geology

Earth has four major main layers: an inner core at the center, an outer core enveloping it, mantle, and crust.

Since it has the greatest density out of all the planets in the solar system - 5.51 g/cm³ - and a gravity of 9.807 m/s² or 1 g the Earth's core is solid. It is made of iron and nickel about 759 miles / 1.221 kilometers in radius. The temperatures at the core have been estimated to be around 9.800 degrees Fahrenheit / 5.400 degrees Celsius. This is hotter than the surface of the Sun.

Together with the inner core, Earth also has an outer core, with the crust being the mantle and the thickest layer. It is a viscous mixture of molten rock about 1.800 mi / 2.900 km thick and has the consistency of caramel.

The outermost layer - Earth's crust - goes about 19 mi / 30 km deep on average on land. But at the bottom of the ocean, the crust is thinner and extends about 3 mi / 5 km from the seafloor to the top of the mantle. The crust in a sense floats on the mantle due to lower density.

It is not a solid piece but rather broken up into huge tectonic plates. These plates move, driven by the flow of rock in the mantle that is in turn powered by heat.

The core heats the bottom of the mantle causing convection leading to the warmer material to rise. It takes about 50.000 to 60.000 years for a blob to move a single kilometer.

Though the hot material rises towards the surface, it is blocked by the crust. The magmatic rock pushes on the plates, causing them to slide around slowly.

Over millions of years, the surface geology of the Earth changed dramatically because of this. Where the crust is weaker magma can push its way through thus erupting onto the surface, forming volcanoes.

Because of volcanoes, material wells out creating new land, and they also pump out gas that greatly contributed to Earth's atmosphere.

The interior of the Earth is very hot - comparable to the surface of the Sun. Most of the heat has remained since the Earth's formation. As it gained mass it began to contract under its own gravity - the squeezing adding heat to the material. Elements like uranium also contribute to the Earth's heat as the atoms radioactively decay.

Another source for the heat: dense materials such as iron and nickel that sunk to the center, warming up due to friction.

As such the core is so hot because of:

Leftover heat since the Earth's formation

Gravity's squeezing effect

Radioactive decay from elements such as uranium

Friction

The surface of the Earth is constantly moving. Molten lava rises from beneath the surface and moves into the gap that is created. The new rock helps push the plates apart and as it cools, it becomes part of the continually regenerating crust.

When the ocean plates meet the continental plates they are forced downward. This creates friction beneath and pressure forces molten rock upward to erupt to the crust as ash and lava.

Many volcanoes formed this way but there is a second type of collision: when two continental plates converge as one plate slides under the other the lighter mass at the surface thrusts and folds upward forming mountain chains.

The third type of plate interaction occurs where plates meet at oblique angles to each other. Pressure and friction between the surfaces prevent slippage and when the tension becomes too great the plates shift, sliding along a fault line. Sometimes, violent tremors result and cause the widespread destruction of an earthquake.

Surface

The surface area of Earth is about 197 million square miles / 510 million square kilometers. Around 71% of the surface is covered by water and 29% by land.

The water is 3% fresh and 97% salted. Of that 3% freshwater, over 2% is frozen in ice sheets and glaciers meaning that less than 1% is freshwater found in lakes, rivers, and the underground.

In regards to land, the continent of Asia covers about 30% of all the land, having around 60% of the world's population. The Earth is divided into 7 continents that constantly "move" several centimeters every year. In about 250 million years about four fundamental scenarios for the formation of the next supercontinent have been hypothesized: Novopangea, Pangea Ultima, Aurica and Amasia.

Novopangea seems the most likely scenario based on current evaluations. The Americas would collide with the northward drifting Antarctica, and then into the already collided Africa-Eurasia.

The highest altitude - elevation - on Earth is Mount Everest at 8,848m \ 29,029 ft above sea level. The lowest point on land is in the Dead Sea - 420 m / 1.377 ft below sea level. The average depth of the global ocean is about 2.5 miles / 4 kilometers. Most volcanoes are hidden under these oceans. Hawaii's Mauna Kea is a volcano much taller than Mount Everest, and even Earth's longest mountain range - four times longer than the Andes, Rockies, and Himalayas combined - is underwater at the bottom of the Arctic and Atlantic oceans.

The shape of the Earth is nearly spherical. There is a small flattening at the poles and bulging around the equator due to Earth's rotation speed. This makes the shape of Earth approximately an oblate spheroid. The point on the surface farthest from Earth's center of mass is the summit of the equatorial Chimborazo volcano in Ecuador.

Atmosphere

The atmosphere of Earth is a layer of gas above the crust. It is not solid and thus it fades away with height. The line between Earth's atmosphere and space is set at 100 km / 62 miles up. It is called the Kármán line. Technically, anyone, who goes above it is an "astronaut."

The atmosphere by volume is about 78% nitrogen, 21% oxygen, 1% argon, and the rest an assortment of trace gases. Water vapor is also present, almost all of it below a height of about 8-15 km/ 4.9 - 9 mi.

This part of the atmosphere is the warmest at the bottom, creating convection in the air that in turn creates currents of rising air. They carry water, forming clouds, which in turn is why we have weather.

The ozone layer is situated at a height of 25 km / 15.5 mi on average. This is a molecule of oxygen that absorbs very well solar ultraviolet light. This type of light is dangerous to biological molecules thus the ozone layer is critical for our protection and survival.

The atmosphere of Earth can be divided into 6 major layers:

(1). Troposphere - The lowest starting at ground level and extending upward to about 10 km / 6.2 miles. Most of the weather occurs here and most clouds are present.

(2). Stratosphere - It extends from the top of the troposphere to about 50 km / 31 mi above the ground. This is where the ozone layer is present. Unlike the troposphere, it gets warmer upwards this means a lack of turbulence favorable to commercial jet plane rides.

(3). Mesosphere - It extends upward to a height of about 85 km / 53 miles above the planet. Most of the meteors burn up in the mesosphere and unlike the stratosphere, the temperature drops again with the top temperature reaching about -90 degrees Celsius / -130 degrees Fahrenheit. The air here is far too thin to breathe and the pressure is well below 1% of the pressure at sea level.

(4). Thermosphere - A layer with very rare air and high-energy X-rays and radiation from the Sun being present but absorbed by the thermosphere. This raises the temperatures considerably and most satellites orbit the Earth in this layer. The auroras, Northern and Southern Lights, occur in the thermosphere. The top of the thermosphere varies between 500-1.000 km / 311-621 mi above the ground.

(5). Exosphere - Considered the final frontier of Earth's gaseous envelope. The air here is extremely thin and leaks into space. The top once again varies: 100.000-190.000 km / 62.000-120.000 mi above the surface of Earth. The latter value is about halfway to the Moon.

(6). Ionosphere - It is not a distinct layer as the previous ones. It is rather a series of regions in parts of the mesosphere and thermosphere where high-energy radiation from the Sun has knocked electrons loose from their parent atoms and molecules. The electrically charged atoms & molecules are called ions endowing this region with some special properties.

Magnetosphere

Earth's outer core is made from liquid metal which conducts electricity. The liquid convects, and this motion generates magnetic fields. Earth's rotation helps organize this motion into huge cylindrical roles that align with the Earth's axis.

This generates a magnetic field similar to a bar magnet, with a magnetic north pole and south pole. This field surrounds the Earth and deflects most of the charged particles from the solar wind. Without this geomagnetic field, the solar wind would directly hit Earth's atmosphere eroding the air away.

Mars doesn't have a strong magnetic field, and it is believed that because of this its atmosphere is mostly vanquished.

Some solar wind particles are trapped by Earth's magnetic field and are channeled down into the atmosphere. There, they are slammed into air molecules about 150 km / 93.2 mi up. This energizes the molecules, which respond by emitting light in different colors. This glow is called aurora.

The auroras happen near the geomagnetic poles, far north and south. They form ribbons and sheets, depending on the shape of the magnetic field.

Analysis revealed that a magnetic reversal takes place once every 40.000 years on average. When it will happen, compass needles would likely point in many different directions for a few centuries while the switch is being made. After this, the south will become north and vice versa.

Axial Tilt

The Earth orbits around the Sun with one pole constantly tilted towards it. This tilt results in how much light reaches a given point on the surface of Earth. Earth's axis is tilted towards the ecliptic of the Sun at approximately 23.4 degrees. This is responsible for Earth's seasonal changes and the diurnal cycle.

Hydrosphere

Earth is currently the only known planet with water on the surface. Referred to as the "Blue Planet", Earth's hydrosphere consists chiefly of oceans, inland seas, lakes, rivers, and underground waters down to a depth of 2.000 m / 6.600 ft.

The deepest underwater location is the Challenger Deep of the Mariana Trench in the Pacific Ocean with a depth of 10.911 m / 35.799 ft. The mass of the oceans represents about 1/4400 of Earth's total mass.

Habitability - Biosphere

Life forms inhabit ecosystems, whose total is sometimes said to form a biosphere. The evolution of the biosphere is speculated to have begun about 3.5 Gya. The biosphere is divided into biomes, inhabited by broadly similar plants and animals. In 2016, scientists reported identifying a set of 335 genes from the last universal common ancestor (LUCA), of all organisms living on Earth.

The origin of life on Earth is still disputed. There are 2 major standing theories that suggest that life developed here from chemical reactions or that life was brought here by a process named panspermia.

Chemical reactions led to the first self-replicating molecules about 4 billion years ago. Half a billion years later, the last common ancestor of all current life arose.

Photosynthesis allowed the Sun's energy to be directly harvested by life forms. The resultant molecular oxygen accumulated in the atmosphere and due to interaction with ultraviolet solar radiation formed a protective ozone layer in the upper atmosphere.

Smaller cells incorporated into larger ones and resulted in the development of complex cells called eukaryotes. Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion years old sandstone in Western Australia.

The panspermia theory suggests that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, and also spacecraft carrying unintended contamination by microorganisms.

Basically, organisms such as extremophiles can become trapped in debris ejected into space after collisions between planets and other small objects. These organisms may travel dormant until arriving at suitable planets that host suitable conditions for life to thrive and evolve.

Cartography

About 80% of Earth's oceans haven't been mapped, and about 65% of the Earth remains unexplored. There are no maps that can actually accurately portray the Earth. The most well-known model - the Mercator - is flawed because the linear scale increases with latitude.

This distorts the size of geographical objects far from the equator and conveys a distorted perception of the overall geometry of the planet.

Probably the most accurate map is the AuthaGraph World Map because it folds the Earth into a three-dimensional globe.

Satellites

Earth has one natural satellite the Moon, and several other artificial satellites such as asteroids or large rocks trapped by Earth's gravity. They are trapped only temporarily for months or even years before returning to an orbit around the Sun.

It is believed that the Moon was formed after a collision billions of years ago. A large chunk of rock smashed into Earth and displaced a portion of Earth's interior. The resulting chunks clumped together and formed our Moon. This is at least the most widespread theory, researching continues.

The Moon

Since ancient time's humanity has used the moon to measure the passing of months due to its moving phases from full moon to new moon and back again.

It is called the moon because it was used to measure the months. The word moon can be traced to the Old English word "mōna." It shares its origin with the Latin words "metri", which means to measure, and "mensis", which means month.

Earth's moon is the fifth largest of all the moons in the solar system. The Moon is pretty big when comparing it to Earth, being a full quarter of the diameter of the planet. This is the biggest ratio, much bigger than for any other moon orbiting a planet.

The Moon has a diameter of about 3.470 km / 2. 156 mi, and on average it is about 380.000 km / 236.121 mi away from Earth. This means that 30 Earth's could fit in between to cover the distance. The Moon has a radius of 1.079 mi / 1.737 km. It's not even wider than the United States.

The Moon has a similar structure to that of the Earth: a solid iron inner core, a liquid outer core, a thick mantle, and a crust of lighter materials on the top.

The core is believed to be around 350 km / 217 in radius with hot temperatures being present but not as high as in Earth's core. The lower mantle may be a thick fluid, but unlike Earth's mantle, the upper part is solid.

The Moon is tidally locked to Earth, meaning it always shows only one side of its surface to us. The side that we see called the near side is divided into two distinct types of regions:

- Highlands, which are heavily cratered

- Maria (Latin for seas), which are darker and smoother.

The Moon may as well act as a shield against space objects. The highlands were cratered by impacts over the eons from asteroid and comet collisions. Rocks from these regions have been dated to be about 4 billion years old, nearly as old as the Moon itself.

The maria region doesn't have nearly as many craters. They are younger, appearing to be about 3.5 billion years old. The maria are made of darker, basaltic material, which means they probably formed from lava flooding older areas.

The dark side of the moon referred to as the "far side" remained a mystery for us for most of our existence. In 1959 the Soviet Union flew the Luna 3 space probe around the Moon, photographing the far side.

Expectations were that the far side would look like the near side. However, the far side was vastly different presenting almost no maria. The crust on the far side is thicker than on the near side.

The only explanation for this has to do with how the moon was formed. The most well-known theory is the Giant Impact hypothesis. A Mars-sized planet slammed into the young Earth, not head-on impact but rather a grazing collision.

The material from both planets was blasted into space and later formed the Moon. Though is it similar to Earth in composition, some rocks show a peculiar ratio of different kinds of oxygen atoms called isotopes, possibly being a piece of strong evidence for this theory. Further, the Moon was probably closer to Earth and suffered from Earth's high temperatures at the time while the far side later suffered during the Late Heavy Bombardment.

There is a possibility that the Moon has water on it. Deep craters near the Moon's poles have floors that never see sunlight. Comet impacts can distribute water all over the Moon, most of it being destroyed by the sunlight however, it can collect in these dark craters.

In fact, water was already discovered on the Moon but the water at the poles remains a bit hypothetical but very probable.

The Moon helps our planet be more livable by moderating Earth's wobble on its axis, leading to a relatively steady climate. It also causes tides, creating a rhythm that has guided humanity for thousands of years.

The Moon used to have active volcanoes but now they are dormant. It also has a thin and weak atmosphere, called an exosphere.

Location

Earth, along with the Solar System, is situated in the Milky Way and orbits about 28,000 light-years from its center. It is about 20 light-years above the galactic plane in the Orion Arm.

The Future

The Earth is constantly gaining and losing mass with the Moon distancing itself from us one inch every year. Humanity must continue to strive and colonize other planets for survival as nothing lasts forever, especially finite materials.

In one billion years the solar luminosity will increase by about 10% causing the atmosphere to become a "moist greenhouse", resulting in a runaway evaporation of the oceans. In about 2-3 billion years Earth's magnetic dynamo may cease. Future missions for the colonization of the Moon are being prepared by several nations as well as other important missions to other worlds.

This hopefully will finally put an end to the flat Earth conspiracy and to the Moon flight conspiracy, and maybe humanity will realize its true capability and raison d'etre, with the hopeful success of future space missions.

Did you know?

If all of Earth's crustal surface were at the same elevation, the depth of the resulting ocean would be 2.7 km / 1.68 mi.

The average salinity of Earth's oceans is about 35 grams of salt per kilogram of seawater - 3.5% salt.

The continents of Earth move at the same rate as human fingernails grow.

The Moon and Earth orbit a common barycenter every 27.32 days relative to the background stars.

The sphere of gravitational influence, of the Earth, is about 1.5 million km (930,000 mi) in radius. This is the maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.

If space were a vacuum, Earth's magnetic field would extend to infinity.

The Moon orbits the Earth roughly as fast as a rifle bullet.

The Earth is gradually rotating slower at about 17 milliseconds per 1.000 years. The Moon contributes to this and as Earth slows down, the Moon creeps away.

The Earth's magnetic field and its interaction with the solar wind also produce the Van Allen radiation belts, a pair of doughnut shaped rings of ionized gas (or plasma) trapped in orbit around the Earth.

The Earth is travelling through space at roughly 67.000 miles 107,826 kilometers per hour.

Earth has a lot fewer craters than the surface of most other planets.This is because the planet has lots of volcanoes and earthquakes which cause the highs and lows of the surface to sink or be worn down over time.

Around 1.300.000 Earth's could fit into the Sun.

The Sun will eventually turn into a red giant and engulf Earth.

The first picture taken of Earth from outer space was conducted by the Apollo 17 team. The original picture portrayed Earth upside-down. The image was later edited.

If 7 billion people were to jump at the same time, a magnitude 4 to 8 earthquake would ensue.

Light pollution prevents one third of Earth's population from seeing the Milky Way galaxy in the night sky.

The Moon has been visited by over 100 space probes.

The rocks brought back by the Apollo 11 team from the moon are still studied to this day.

Sources:

Image sources:

1. https://upload.wikimedia.org/wikipedia/commons/thumb/9/97/The_Earth_seen_from_Apollo_17.jpg/767px-The_Earth_seen_from_Apollo_17.jpg

2. https://en.wikipedia.org/wiki/Heliocentrism#/media/File:Heliocentric.jpg

3. https://www.universetoday.com/58177/earth-formation/

4. https://www.xearththeory.com/wp-content/uploads/expanding-earth-7.jpg

5. https://en.wikipedia.org/wiki/Solar_System#/media/File:Planets2013.svg

6. https://en.wikipedia.org/wiki/Earth%27s_orbit#/media/File:Geoz_wb_en.svg

7. https://en.wikipedia.org/wiki/Structure_of_the_Earth#/media/File:Earth_poster.svg

8. https://en.wikipedia.org/wiki/Geology#/media/File:Active_Margin.svg

9. https://en.wikipedia.org/wiki/Geology#/media/File:San_Andreas.jpg

10. https://speculativeevolution.fandom.com/wiki/Novopangea?file=Novopangea.jpg

11. https://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Earth2014shape_SouthAmerica_small.jpg/661px-Earth2014shape_SouthAmerica_small.jpg

12. https://upload.wikimedia.org/wikipedia/commons/d/df/Full_moon_partially_obscured_by_atmosphere.jpg

13. https://ichef.bbci.co.uk/news/660/cpsprodpb/169F1/production/_84575629_magneticfield.jpg

14. http://4k.com/wp-content/uploads/2015/12/oval.png

15. https://en.wikipedia.org/wiki/Earth#/media/File:Earth_elevation_histogram_2.svg

16. https://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png

17. https://upload.wikimedia.org/wikipedia/commons/c/c8/PhylogeneticTree%2C_Woese_1990.svg

18. https://upload.wikimedia.org/wikipedia/commons/thumb/4/48/Panspermie.svg/800px-Panspermie.svg.png

19. https://www.dailymail.co.uk/sciencetech/article-3894600/The-map-shows-world-REALLY-looks-like-Japanese-design-flattens-Earth-big-landmasses-oceans-really-are.html

20. https://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/FullMoon2010.jpg/808px-FullMoon2010.jpg

21. https://steemitimages.com/p/54TLbcUcnRm4iYtFdzVNy1kt3F2tvRShXkTnWxjMqVpHRnm2gJV24YjCgcjmRNxfuD6FVEdRmTwntCaQ3rLKaFLRQKEWJwFkzKbfzGCs91BWWJ8Q8WqqVqdWg625ziFL1dPEdhbeW?format=match&mode=fit&width=640

22. https://swh-826d.kxcdn.com/wp-content/uploads/2011/04/Lunar-Maria.jpg

23. https://images.theconversation.com/files/108549/original/image-20160119-29756-1frh5c9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=926&fit=clip

24. https://en.wikipedia.org/wiki/Moon#/media/File:LRO_WAC_South_Pole_Mosaic.jpg

25. https://en.wikipedia.org/wiki/Milky_Way#/media/File:Galactic_longitude.JPG

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Earth Facts | Surface, Atmosphere, Satellites, History & Definition

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Earth is the third planet from the Sun and the fifth largest planet in the Solar System with the highest density. It is currently the only known location where life is present. The realization that Earth is a planet, and a planet among many others was established "fairly" recently, in the 17th century - this realization came through by the combined forces of ancient philosophers, mathematicians, and astronomers.

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One of the brightest planets - Venus.

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Venus - Educational facts and history of the planet Venus.

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Venus is the second planet from the Sun and the sixth largest. Venus' orbit is the most nearly circular of that of any planet, with an eccentricity of less than 1%.

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Read all about Mercury - the planet closest to the sun.

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Mercury is the closest planet to the Sun but, perhaps surprisingly, it does not have the highest temperatures. It is the second densest planet of the Solar System, but also the smallest planet. The structure of Mercury makes it the most similar planet to Earth.
Key Facts & Summary

Since Mercury can be seen without the need of a telescope, many ancient civilizations saw the planet, and as such it is impossible to determine who discovered it first. However, it was first observed with the help of a telescope in early 17th century, by Galileo Galilei.

Galileo's crude telescope didn't manage to capture Mercury's phases, this would be observed later by astronomer Giovanni Zupi in 1639, and thus he discovered that the planet had similar phases like Venus and the Moon.

In ancient times, Mercury was taught as being two different objects in the sky: The Mourning Star and The Evening Star. In Venus's case, it was also mistakenly believed to be two different things.

Venus spends most of its time away from Earth. This paradoxically makes Mercury the closest planet to Earth, a plurality of the time.

Mercury was named after the Roman messenger god, because of its fast movements around the Sun.

Mercury is the closest planet to the Sun at a distance of 57.91 million kilometers / 35.98 miles or 0.4 AU away. It takes sunlight 3.2 minutes to travel from the Sun to Mercury.

Despite its closeness to the Sun, it is not the hottest planet, that title belongs to Venus but Mercury is the fastest planet, completing a trip around the Sun in 88 Earth days. This also makes one year on Mercury the equivalent of 88 Earth days, the shortest year of any planet.

It orbits around the Sun with a speed of about 29 miles or 47 kilometers per second.

Despite being the smallest terrestrial planet from the Solar System, and in fact the smallest of all the planets, it is the second densest planet in the Solar System, with a density of 5.43 g/cm³.

For a comparison, Mercury's size is about a third of Earth, and Earth has a density of 5.51 g/cm³.

Mercury has a radius of 2.439 km or 1516 mi, and a diameter of 4.879 km or 3.032 mi.

Mercury's axis has the smallest tilt of any of the Solar System's planets at about ​¹⁄₃₀ degrees, while its orbital eccentricity is the largest of all known planets in the Solar System.

Mercury's distance from the Sun is only about two-thirds or 66%, of its distance at aphelion, at its aphelion it is 0.44 AU away from the Sun.

At its closest distance or perihelion, it is 0.30 AU away from the Sun.

Mercury spins slowly on its axis and completes one rotation every 59 Earth days. One Mercury solar day or one full day-night cycle, equals 176 Earth days-just over two years on Mercury. (Reminder, one year on Mercury is 88 Earth days)

Mercury does not have any known satellites or ring systems.

Its surface is very similar to Earth's Moon, implying that the planet hasn't been geologically active for many years.

Instead of an atmosphere, Mercury possesses a thin exosphere made up of atoms blasted off the surface by the solar wind and striking meteoroids. Mercury's exosphere is composed mostly of oxygen, sodium, hydrogen, helium and potassium.

Temperatures on the surface of Mercury are both hot and cold. During the day, temperatures on the surface can reach up to 800 degrees Fahrenheit / 430 degrees Celsius. Because the planet has no atmosphere to retain that heat, nighttime temperatures on the surface can drop to -290 degrees Fahrenheit / -180 degrees Celsius. These changes in temperature are the most drastic in the entire Solar System.

Mercury's magnetic field is offset relative to the planet's equator. Though the magnetic field at the surface has just 1.1% the strength of Earth's, it interacts with the magnetic field of the solar wind to sometimes create intense magnetic tornadoes that funnel the fast, hot solar wind plasma down to the surface of the planet.

Mercury rotates in a way that is unique in the Solar System. It is tidally locked with the Sun in a 3:2 spin-orbit resonance.

Mercury and Venus orbit the Sun within Earth's Orbit, this makes them inferior planets.

One of the earliest known recorded observations of Mercury is the Mul.Apin tablets. It is believed that these observations were made by an ancient Assyrian astronomer around 14 th century BC. The name used in these tablets is translated as "the jumping planet".

Some Babylonian records date back to the 1 st millennium BC. They called the planet Nabu, after the messenger to the gods in their mythology. The ancient Greeks knew the planet as Hermes while the Romans named it Mercury and it remained as such to this day.

Credits cannot be given to a single civilization or person because the planet has always been easy to spot on the sky. What we can do is to give credit to those who first studied the planet by more "modern" means such as Galileo Galilei in the early 17 th century, and Giovanni Zupi who in 1639, observed that the planet had phases just like Venus and the Moon.

Formation

It is theorized that Mercury was formed about 4.5 billion years ago when gravity pulled swirling gas and dust together to form the small planet. Its small size but enormous core is theorized to be the result of a collision with another giant object that stripped much of its surface.

Distance, Size and Mass

Mercury is the closest planet to the Sun, at a distance of 57.91 million kilometers / 35.98 miles or 0.4 AU away. It takes sunlight 3.2 minutes to travel from the Sun to Mercury.

Mercury has a radius of 2.439 km or 1516 mi, and a diameter of 4.879 km or 3.032 mi. It is about the size of the continental United States, slightly bigger. It has a mass of about 3.285 × 10^23 kg or about 5.5% that of Earth.

Despite being the smallest planet from the Solar System, it is the second densest planet in the Solar System, with a density of 5.43 g/cm³ after Earth. For comparison, Mercury's size is about a third of Earth, and Earth has a density of 5.51 g/cm³.

Orbit and Rotation

Mercury's highly eccentric, egg-shaped orbit takes the planet as close as 29 million miles or 47 million kilometers, and as far as 43 million miles or 70 million kilometers from the Sun. It takes a trip around the Sun every 88 days thus 1 orbit/year is the equivalent of 88 Earth days. Mercury travels through space at nearly 29 miles or 47 kilometers per second, faster than any other planet.

The diagram above illustrates the effects of the eccentricity, showing Mercury's orbit overlaid with a circular orbit having the same semi-major axis. The resonance makes a single solar day on Mercury last exactly two Mercury years, about 176 Earth days.

Radar observations in 1965 proved that the planet has a 3:2 spin-orbit resonance, rotating three times for every two revolutions around the Sun. The eccentricity of Mercury's orbit makes this resonance stable at perihelion, when the solar tide is strongest. The Sun is nearly still in Mercury's sky. The orbital eccentricity of Mercury in simulations varies chaotically, from zero or circular to more than 0.45 over millions of years because of the perturbations of the other planets.

More accurate modeling based on a realistic model of tidal response has demonstrated that Mercury was captured into the 3:2 spin-orbit state at a very early stage of its history, within 20 or 10 million years after its formation.

Mercury spins slowly on its axis and completes one rotation every 59 Earth days. But when Mercury is moving fastest in its elliptical orbit around the Sun, and it is closest to the Sun, each rotation is not accompanied by a sunrise and sunset like on most other planets. The morning Sun appears to rise briefly.

It then sets and rises again from some parts of the planet's surface. The same thing happens in reverse at sunset for other parts of the surface. Mercury travels in an elliptical orbit slowing down when it's farther from the Sun, and accelerating as it draws closer.

Axial tilt

The axial tilt is almost zero, with the best measured value as low as 0.027 degrees. This is significantly smaller than that of Jupiter, which has the second smallest axial tilt of all planets at 3.1 degrees. On average, Mercury is the closest planet to Earth, and to each of the other planets in the Solar System.

Surface and Geology

Very similar in appearance to Earth's moon, Mercury's surface is scarred by many impact craters from comets or meteoroids. Interestingly, many of these craters are named after famous deceased artists and authors. There are also extensive mare-like plains present and the craters also indicate that the planet has been geologically inactive for billions of years.

It is believed that Mercury was heavy bombarded by comets and asteroids during and shortly after its formation 4.6 billion years ago, as well as during a possibly separate subsequent event called the Late Heavy Bombardment that ended 3.8 billion years ago.

During this bombardment, Mercury's entire surface suffered even more because of its lack of atmosphere that would have slowed impacts down. It is believed that Mercury was volcanically active during this period.

Basins such as the Caloris Basin were filled with magma, producing smooth plains similar to the lunar marias found on the Moon.

The largest known crater is Caloris Basin, with a diameter of 1,550 km or 963 miles. About 15 impact basins have been identified on Mercury, with more to be revealed.

Two geologically distinct plains regions on Mercury have been identified. Gently rolling, hilly plains the regions between craters are Mercury's oldest visible surfaces, predating the heavily cratered terrain.

These crater plains appear to have obliterated many earlier craters. Unlike lunar maria, the smooth plains of Mercury have the same albedo as the older inter-crater plains. Another interesting feature of Mercury's surface is the numerous compression folds or rupes that crisscross plains. A theory suggests that as Mercury's interior cooled, it contracted and its surface began to deform, creating wrinkle ridges and lobate scarps associated with thrust faults. These features have indicated that Mercury's radius became smaller, shrinking in the range of 1 to 7 km or 4 miles.

Other factors indicate that this shrinking and geological activity may be present to this day. The volcanic system on Mercury is quite complex, though its exact age is hard to pinpoint but it is speculated to be billions of years old.

Temperatures on the surface of Mercury are both hot and cold. During the day, temperatures on the surface can reach up to 800 degrees Fahrenheit / 430 degrees Celsius. Because the planet has no atmosphere to retain that heat, nighttime temperatures on the surface can drop to -290 degrees Fahrenheit / -180 degrees Celsius. These changes in temperature are the most drastic in the entire Solar System.

Structure

Mercury is a terrestrial planet having three main layers: a core, mantle and crust. Mercury's crust has no tectonic plates and its iron core is enormous, making up 85% of the planets radius while Earth's inner and outer core, account for about 55%.

Because of the core's unusual size, it influences Mercury's overall size by causing it to shrink. The iron core has slowly cooled and contracted for about 4.5 billion years. By doing this, it pulled the surface inward, and thus has reduced the planet's size between 1 - 7 km or 4 miles.

The planet consists of about 70% metallic and 30% silicate material leading to its high density and thus placing it as the second densest planet. It is believed that if the effects of the gravitational compression were to be factored out from both Mercury and Earth, Mercury would take the first place as the densest.

This density also indicates that its core is huge and rich in iron. Mercury's crust is estimated to be around 35 km or 22 mi thick.

Atmosphere - Exosphere

Because of its proximity to the Sun, Mercury's gravity is strongly affected. It is too small and hot for its gravity to retain any significant atmosphere over long periods of time. The surface temperature of Mercury ranges from 100 to 700 K (−173 to 427 °C; −280 to 800 °F) at the most extreme places but it never rises above 180 K at the poles, due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles.

Thus Mercury does not have an atmosphere, but it does have a thin exosphere. The exosphere is traditionally the outermost layer of a planet's atmosphere. Mercury's exosphere is made up of oxygen, sodium, hydrogen, helium and potassium that are all whipped up from the planet's surface by the solar winds.

Although the daylight temperature at the surface of Mercury is generally extremely high, observations strongly suggest that ice / frozen water, exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K, far lower than the global average.

Water ice strongly reflects radar, and observations by the 70-meter Goldstone Solar System Radar and the VLA in the early 1990s revealed that there are patches of high radar reflection near the poles. Although ice was not the only possible cause of these reflective regions, astronomers think it was the most likely.

Magnetosphere

Even if it is small and has a slow 59-day-long rotation, Mercury has a significant and apparently global magnetic field. It has been estimated that this magnetic field has 1.1% the strength of Earth's. The strength at its equator is about 300 nT, and like that of Earth's it is dipolar. The difference is that Mercury's poles are nearly aligned with the planet's spin axis.

It is speculated that the magnetic field is generated by a dynamo effect, similar to the magnetic field of Earth. This effect would be resulted from the circulation of the planet's iron-rich liquid core. Particularly strong tidal effects caused by the planet's high orbital eccentricity would serve to keep the core in the liquid state necessary for this dynamo effect.

The magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. It interacts with the magnetic field of the solar wind to sometimes create intense magnetic tornadoes that funnel the fast, hot solar wind plasma down to the surface of the planet.

Life Habitability

Extreme temperatures both cold and hot make it unlikely that life may develop there. The temperatures and solar radiation that characterize this planet are most likely too extreme for organisms to adapt to.

Satellites

Mercury doesn't have any known satellites even though many objects much smaller than Mercury have. It is believed that moons form in the same time as their parent planets and in the case of Mercury, all the materials around it were used up by the planet leaving almost nothing left so that a moon could be formed.

Another theory suggests that Mercury couldn't have a moon because of its closeness to the Sun. Because of this, the Sun's greater gravity force would overcome that of Mercury and pull any objects around it, towards itself. Overall, Mercury's closeness to the sun prevents it from ever having a satellite.

Future plans for Mercury

Because of Mercury's closeness to Earth, it will always be a target for missions and further observations. The third spacecraft set to arrive on Mercury is called BepiColombo, and it is planned to arrive at Mercury in 2025.

Did you know?

- From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter.

- NASA's spacecraft Mariner 10 was the first mission to explore Mercury in 1974-1975.

- NASA's spacecraft MESSENGER was the first to orbit Mercury in 2008.

- Mercury's apparent distance from the Sun as viewed from Earth never exceeds 28°.

- You could fit approximately 21,253,933 Mercuries inside the Sun.

- In ancient China, Mercury was known as "the hour Star" - being associated with the direction of the north.

- Modern Chinese, Korean, Japanese and Vietnamese cultures refer to the planet as "water star."

- Hindu mythology used the name "Buddha graha" to refer to Mercury. This god was thought to preside over Wednesday.

- The god Odin or Woden of Germanic paganism was associated with the planet Mercury and also Wednesday.

- Maya people may have represented Mercury as an owl that served as a messenger to the underworld.

- Mercury can, like several other planets and the brightest stars, be seen during a total solar eclipse.

- Even though Mercury is a planet, it is even smaller than the largest natural satellites in the Solar System: Ganymede and Titan, albeit Mercury is more massive.

- Mercury's core has a higher iron content than that of any other major planet in the Solar System.

- Your weight on Mercury would be 38% of your weight on Earth as Mercury has a gravity of 3.7 m/s², while Earth has 9.807 m/s².

- The most cratered planet in the solar system is Mercury.

- NASA has mapped the entire surface of Mercury.

- It is believed that Mercury has a tail: it streams of particles sloughing off its surface.

- The naming and discovery of Mercury cannot be attributed to anyone.

- The crater Caloris Basin is large enough to fit in the state of Texas.

- An event called a "transit" occurs 13 times every century making it possible to see Mercury from Earth, as it crosses the Sun's face.

- Mercury is about 50% larger in diameter than Earth's Moon.

- It would take about 18 Mercury's to match Earth.

- Mercury doesn't experience any seasons.

- It is one of the most popular planets in our imagination.

- Mercury is about twice as large as Pluto.

[1.] Wikipedia

[1.] https://upload.wikimedia.org/wikipedia/commons/d/d9/Mercury_in_color_-_Prockter07-edit1.jpg

[2.] https://www.universetoday.com/35960/size-of-the-planets/

[3.] https://en.wikipedia.org/wiki/File:ThePlanets_Orbits_Mercury_PolarView.svg

[4.] https://en.wikipedia.org/wiki/File:Mercury%27s_orbital_resonance.svg

[5.] https://en.wikipedia.org/wiki/File:Unmasking_the_Secrets_of_Mercury.jpg

[6.] https://en.wikipedia.org/wiki/File:PIA19450-PlanetMercury-CalorisBasin-20150501.jpg

[7.] https://en.wikipedia.org/wiki/Caloris_Planitia#/media/File:The_Mighty_Caloris_(PIA19213).png

[8.] https://en.wikipedia.org/wiki/Inter-crater_plains_on_Mercury#/media/File:Rudaki_CW0131770591G_web.png

[9.] https://en.wikipedia.org/wiki/File:Mercury%27s_internal_structure1.jpg

[10.] https://en.wikipedia.org/wiki/File:PIA19421-Mercury-Craters-MunchSanderPoe-20150416.jpg

[11.] https://en.wikipedia.org/wiki/File:North_pole_of_Mercury_-_NASA.jpg

[12.] https://en.wikipedia.org/wiki/File:Merc_fig2sm.jpg

[13.] https://en.wikipedia.org/wiki/File:Mercury_Magnetic_Field_NASA.jpg

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Mercury Facts | Information, History, Location, Size & Definition

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Mercury is the closest planet to the Sun but, perhaps surprisingly, it does not have the highest temperatures. It is the second densest planet of the Solar System, but also the smallest planet. The structure of Mercury makes it the most similar planet to Earth.