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Our Solar System: A Guide for Young Explorers

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Our Solar System: A Guide for Young Explorers

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An engaging overview of our solar system, written specifically for young readers. Includes colorful illustrations and easy-to-understand explanations of planetary facts.

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A comprehensive online resource featuring kid-friendly articles about the solar system, with interactive elements and updated scientific information.

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Articles, games and activities about our planetary neighbors

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Learn about Mercury's extreme temperatures, cratered surface, and why it's the fastest planet in our solar system.

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Mercury is the closest planet to the sun and also the smallest planet in the solar system.

The small and cratered planet does not have any moons and zips around the sun faster than any other planet in the solar system, hence why the Romans named it after their swift-footed messenger god.

It is the second densest planet after Earth, with a huge metallic core roughly 2,200 to 2,400 miles (3,600 to 3,800 kilometers) wide, or about 75% of the planet's diameter. In comparison, Mercury's outer shell is only 300 to 400 miles (500 to 600 km) thick. The combination of its massive core and composition, which includes an abundance of volatile elements, has left scientists puzzled for years.

The Sumerians also knew of Mercury at least 5,000 years ago. It was often associated with Nabu, the god of writing, according to a site connected to NASA's MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) mission.

Mercury was also given separate names for its appearance as both a morning star and an evening star. Greek astronomers knew, however, that the two names referred to the same body, and Heraclitus, around 500 B.C., correctly thought that both Mercury and Venus orbited the sun, not Earth.

How hot is Mercury?

Because the planet is so close to the sun, Mercury's surface temperature can reach a scorching 840 degrees Fahrenheit (450 degrees Celsius). However, since this world doesn't have much of a real atmosphere to entrap any heat, at night temperatures can plummet to minus 275 degrees Fahrenheit (minus degrees 170 Celsius), a temperature swing of more than 1,100 degrees Fahrenheit (600 degrees Celsius), the greatest in the solar system.

How big is Mercury?

Mercury is the smallest planet in the solar system - it is only slightly larger than Earth's moon. Since it has no significant atmosphere to stop impacts, the planet is pockmarked with craters. About 4 billion years ago, an asteroid roughly 60 miles (100 km) wide struck Mercury with an impact equal to 1 trillion 1-megaton bombs, creating a vast impact crater roughly 960 miles (1,550 km) wide. Known as the Caloris Basin, this crater could hold the entire state of Texas. Another large impact may have helped create the planet's odd spin, according to research in 2011.

Mercury surface characteristics

As close to the sun as Mercury is, in 2012, NASA's MESSENGER spacecraft discovered water ice in the craters around its north pole, where regions may be permanently shaded from the heat of the sun. The southern pole may also contain icy pockets, but MESSENGER's orbit did not allow scientists to probe the area. Comets or meteorites may have delivered ice there, or water vapor may have outgassed from the planet's interior and frozen out at the poles.

(Image credit: NASA/Bill Ingalls)

Average distance from the sun: 35,983,095 miles (57,909,175 km). By comparison: 0.38 Earth's distance from the sun

Perihelion (closest approach to sun): 28,580,000 miles (46,000,000 km). By comparison: 0.313 times that of Earth

Aphelion (farthest distance from sun): 43,380,000 miles (69,820,000 km). By comparison: 0.459 times that of Earth

Day length: 58.646 Earth days

Color: Gray

As if Mercury isn't small enough, it not only shrank in its past but is continuing to shrink today, according to a 2016 report. The tiny planet is made up of a single continental plate over a cooling iron core. As the core cools, it solidifies, reducing the planet's volume and causing it to shrink. The process crumpled the surface, creating lobe-shaped scarps or cliffs, some hundreds of miles long and soaring up to a mile high, as well as Mercury's "Great Valley," which at about 620 miles long, 250 miles wide and two miles deep (1,000 by 400 by 3.2 km) is larger than Arizona's famous Grand Canyon and deeper than the Great Rift Valley in East Africa.

"The young age of the small scarps means that Mercury joins Earth as a tectonically active planet with new faults likely forming today as Mercury's interior continues to cool and the planet contracts," Tom Watters, Smithsonian senior scientist at the National Air and Space Museum in Washington, D.C., said in a NASA statement.

Indeed, a 2016 study of cliffs on Mercury's surface suggested the planet may still rumble with earthquakes, or "Mercuryquakes." In addition, in the past, Mercury's surface was constantly reshaped by volcanic activity. However, another 2016 study suggested Mercury's volcano eruptions likely ended about 3.5 billion years ago.

One 2016 study suggested that Mercury's surface features can generally be divided into two groups - one consisting of older material that melted at higher pressures at the core-mantle boundary, and the other of newer material that formed closer to Mercury's surface. Another 2016 study found that the dark hue of Mercury's surface is due to carbon. This carbon wasn't deposited by impacting comets, as some researchers suspected - instead, it may be a remnant of the planet's primordial crust.

Mercury's magnetic field

A completely unexpected discovery made by Mariner 10 was that Mercury possessed a magnetic field. Planets theoretically generate magnetic fields only if they spin quickly and possess a molten core. But Mercury takes 59 days to rotate and is so small - just roughly one-third Earth's size - that its core should have cooled off long ago.

"We had figured out how the Earth works, and Mercury is another terrestrial, rocky planet with an iron core, so we thought it would work the same way," Christopher Russell, a professor at the University of California, Los Angeles, said in a University of California, Los Angeles statement.

An unusual interior could help to explain the differences in Mercury's magnetic field when compared to Earth. Observations from MESSENGER revealed that the planet's magnetic field is approximately three times stronger in its northern hemisphere than in its southern. Russell co-authored a model that suggests that Mercury's iron core may be turning from liquid to solid at the core's outer boundary rather than the inner.

"It's like a snow storm in which the snow formed at the top of the cloud and middle of the cloud and the bottom of the cloud too," said Russell. "Our study of Mercury's magnetic field indicates iron is snowing throughout this fluid that is powering Mercury's magnetic field."

The discovery in 2007 by Earth-based radar observations that Mercury's core may still be molten could help explain its magnetism, though the solar wind may play a role in dampening the planet's magnetic field.

Although Mercury's magnetic field is just 1% the strength of Earth's, it is very active. The magnetic field in the solar wind - the charged particles streaming off the sun - periodically touches upon Mercury's field, creating powerful magnetic tornadoes that channel the fast, hot plasma of the solar wind down to the planet's surface.

Does Mercury have an atmosphere?

Instead of a substantial atmosphere, Mercury possesses an ultra-thin "exosphere" made up of atoms blasted off its surface by solar radiation, the solar wind and micrometeoroid impacts. These quickly escape into space, forming a tail of particles, according to NASA.

The atmosphere of Mercury is a "surface-bound exosphere, essentially a vacuum." It contains 42% oxygen, 29% sodium, 22% hydrogen, 6% helium, 0.5% potassium, with possible trace amounts of argon, carbon dioxide, water, nitrogen, xenon, krypton and neon, according to NASA.

Mercury's orbit

Mercury speeds around the sun every 88 Earth days, traveling through space at nearly 112,000 mph (180,000 km/h), faster than any other planet. Its oval-shaped orbit is highly elliptical, taking Mercury as close as 29 million miles (47 million km) and as far as 43 million miles (70 million km) from the sun. If one could stand on Mercury when it is nearest to the sun, it would appear more than three times as large as it does when viewed from Earth.

(Image credit: Karl Tate, SPACE.com)

Oddly, due to Mercury's highly elliptical orbit and the 59 Earth-days or so it takes to rotate on its axis, when on the scorching surface of the planet, the sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset, the sun appears to set, rise again briefly, and then set again.

In 2016, a rare transit of Mercury happened, where the planet crossed the face of the sun as seen from Earth. Mercury's transit may have yielded secrets about its thin atmosphere, assisted in the hunt for worlds around other stars, and helped NASA hone some of its instruments.

As Mercury takes just Earth days to orbit the sun and Earth takes 365 days, approximately three or four times a year Mercury overtakes Earth during its trip around the sun and an optical illusion occurs, according to The New York Times. Mercury appears to move "backward" across the sky for about three weeks, it is during this time Mercury is said to be in retrograde. Astrologers consider Mercury in retrograde to be a time of misfortune and miscommunication as the perceived backward motion interferes with the planet's rules, according to Dictionary.com. The retrograde motion is explained in this YouTube video from Vox.

Mercury Q&A with an expert

We asked Larry Nittler, a cosmochemist who studies the origin and evolution of the solar system at Arizona State University, some questions about Mercury.

What are some of the most fascinating aspects of this planet?

What surprising things about Mercury have we discovered recently?

Mercury missions and research

The first spacecraft to visit Mercury was Mariner 10, which imaged about 45% of the surface and detected its magnetic field.

NASA's MESSENGER orbiter was the second spacecraft to visit Mercury. When it arrived in March 2011, it became the first spacecraft to orbit the planet. The mission came to an abrupt end on April 30, 2015, when the spacecraft, which had run out of fuel, purposely crashed onto the planet's surface for scientists to observe the results.

In 2012, scientists discovered a group of meteorites in Morocco that they think could have originated from the planet Mercury. If so, it would make the rocky planet a member of a very select club with samples available on Earth; only the moon, Mars and the large asteroid Vesta have verified rocks in human laboratories.

In 2016, scientists released the first-ever global digital-elevation model of Mercury, which combined more than 10,000 images acquired by MESSENGER to take viewers across the wide-open spaces of the tiny world. The model revealed the planet's highest and lowest points - the highest is found just south of Mercury's equator, sitting 2.78 miles (4.48 km) above the average elevation of the planet, while the lowest point resides in Rachmaninoff basin, the suspected home of some of the most recent volcanic activity on the planet, and lies 3.34 miles (5.38 km) below the landscape average.

In 2018, a new Mercury explorer was launched. The BepiColombo mission jointly operated by the European and Japanese space agencies is composed of two spacecraft - Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter - that, after a long trek to Mercury, will split up to better understand the tiny world. The European Space Agency's segment of the mission will focus on studying Mercury's surface while the Japan Aerospace Exploration Agency's portion will focus on the planet's strange magnetosphere.

In 2021, BepiColumbo captured its first views of Mercury during a gravity assist flyby. BepiColumbo is scheduled to arrive at Mercury in late 2025, and gather data during its one-year nominal mission with the possibility of a one-year extension, according to ESA.

Mercury images

Mercury quiz

Additional resources

Learn more about Mercury at NASA's Solar System Exploration website. Read about MESSENGER's top science results via Johns Hopkins Applied Physics Laboratory. See MESSENGER's crater on Mercury, made when the spacecraft deliberately crashed into the planet

Bibliography

Strom, Robert G., and Ann L. Sprague. Exploring Mercury: the iron planet. New York: Springer, 2003.

Charlier, Bernard, and Olivier Namur. " The origin and differentiation of planet Mercury." Elements: An International Magazine of Mineralogy, Geochemistry, and Petrology 15.1 (2019): 9-14.

Mangano, Valeria, et al. " BepiColombo science investigations during cruise and flybys at the Earth, Venus and Mercury." Space Science Reviews 217.1 (2021): 1-81.

Hauck, Steven A., and Catherine L. Johnson. " Mercury: Inside the iron planet." Elements: An International Magazine of Mineralogy, Geochemistry, and Petrology 15.1 (2019): 21-26.

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Planet Mercury: Facts About the Planet Closest to the Sun

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Mercury is the closest planet to the sun and the smallest planet in the solar system. We explore Mercury along with its short years, long days and odd sunsets.

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Discover why Venus is called Earth's twin, its unique rotation, and why it's the hottest planet in our solar system.

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LOCATION: Second rock from the sun

DISTANCE FROM THE SUN: 66,782,596 to 67,693,905 miles (107,477,000 to 108,939,000 kilometers)

AVERAGE SURFACE TEMPERATURE: 867° F (462° C)

LENGTH OF SPACE JOURNEY FROM EARTH TO VENUS: 6 months

GRAVITY: If you weigh 100 pounds on Earth, you'd weigh 91 pounds here.

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Mission to Venus - Get facts about this planet

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LOCATION: Second rock from the sun DISTANCE FROM THE SUN: 66,782,596 to 67,693,905 miles (107,477,000 to 108,939,000 kilometers) AVERAGE SURFACE TEMPERATURE: 867° F (462° C) LENGTH OF SPACE JOURNEY FROM EARTH TO VENUS: 6 months GRAVITY: If you weigh 100 pounds on Earth, you'd weigh 91 pounds here.

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Explore what makes Earth unique in our solar system, including its atmosphere, water, and life-supporting conditions.

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Earth and space sciences investigate processes that operate on Earth and address Earth's place in the solar system and galaxy, involving phenomena that range in scale from the unimaginably large to invisibly small.

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Earth and space sciences investigate processes that operate on Earth and address Earth’s place in the solar system and galaxy, involving phenomena that range in scale from the unimaginably large to invisibly small.

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Read about Mars' red color, its moons, and why scientists think it might have once had water like Earth.

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Mars - the fourth planet from the Sun - is a dusty, cold, desert world with a very thin atmosphere. This dynamic planet has seasons, polar ice caps, extinct volcanoes, canyons and weather.

Mars has two small moons, Phobos and Deimos, that may be captured asteroids. They're potato-shaped because they have too little mass for gravity to make them spherical.

A large canyon system called Valles Marineris is long enough to stretch from California to New York - more than 3,000 miles (4,800 kilometers). This Martian canyon is 200 miles (320 kilometers) at its widest and 4.3 miles (7 kilometers) at its deepest. That's about 10 times the size of Earth's Grand Canyon.

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Mars is one of the most explored bodies in our solar system, and it's the only planet where we've sent rovers to roam the alien landscape.

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Learn about Jupiter's Great Red Spot, its many moons, and why it's the largest planet in our solar system.

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Discover the beauty of Saturn's rings, their composition, and the planet's unique features.

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Find out why Uranus appears to roll like a ball around the Sun and learn about its unusual moons.

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Fun Kids - the UK's children's radio station

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Plus you can learn more about what's in our Solar System with our Top 10 Facts on the Sun and the Moon; the planets Earth, Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune and the dwarf planet Pluto.

Welcome to our list of the Top 10 Facts about Uranus! Uranus is the seventh planet from the Sun and the third-largest in the Solar System. It is one of the four giant planets in the Solar System, and it has a unique blue-green colour, due to its methane-rich atmosphere. Uranus is also notable for its tilted orbit, which is tipped by almost 98 degrees. Discover more interesting facts about Uranus below.

1. Uranus is the seventh planet from the Sun

Uranus is the sixth planet from the Sun in our Solar system

2. It was the first planet to be discovered through a telescope

It was the first planet found with a telescope. Other planets like Venus could be seen in the night sky without a telescope however Uranus cannot.

Uranus was discovered in 1781 by an astronomer called William Herschel, although he originally thought it was either a comet or a star.

3. You could fit 63 Earths inside Uranus.

It has a diameter of 25,362 km.

4. Uranus is an 'Ice Giant'

Uranus is an ice giant. It's made up of dense "icy" materials, mainly water, methane and ammonia - above a small rocky core.

5. Uranus has 13 rings

Uranus has two sets of rings.

The inner rings are dark and grey whereas the outer rings are blue and red.

6. The discoverer of Uranus wanted it to be called Georgium Sidus

William Herschel tried unsuccessfully to name his discovery Georgium Sidus after King George III. Instead, the planet was named for Uranus, after the Greek god of the sky. This makes sense because the other planets are also named after Gods.

7. Uranus is the only planet not named after a Roman God

All of the other planets in the solar system are named after Roman Gods except Uranus. Instea d Uranus is named after a Greek God. The Roman equivalent of Uranus is Caelus.

8. Uranus' Moons are named after Shakespeare characters

Uranus has 27 known moons, and they are named after characters from the works of William Shakespeare and Alexander Pope.

These names include Titania from A Midsummer Night's Dream, Prospero from The Tempest and Cordelia from King Lear

9. Uranus formed 4.5 billion years ago

Uranus took shape when the rest of the solar system formed about 4.5 billion years ago. Uranus likely formed closer to the Sun and moved to the outer solar system about 4 billion years ago. Neptune also did this.

10. A day on Uranus is only 17 hours and a year is 84 Earth years

One day on Uranus takes about 17 hours which is the time it takes for Uranus to rotate on its axis once. And Uranus makes a complete orbit around the Sun (a year in Uranian time) in about 84 Earth years - so you'd probably only have 1 birthday in your whole life if you lived on Uranus.

Let's keep learning with our Top 10 Facts about Space and Top 10 Facts about the Solar System. Plus you can learn more about what's in our Solar System with our Top 10 Facts on the Sun and the Moon; the planets Earth, Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune and the dwarf planet Pluto.

Plus check out our video on some of the other awesome things going on in our Solar System

Learn more about Space with Deep Space High below!

Send us your favourite facts!

Is there something we've missed? Got a fact you're dying to tell us? Submit it below and we could use it on a future Top 10 Facts page!

Remember to always ask an adult before filling out forms online.

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Top 10 Facts about Uranus - Fun Kids - the UK's children's radio station

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Plus you can learn more about what's in our Solar System with our Top 10 Facts on the Sun and the Moon; the planets Earth, Mercury, Venus, Mars, Jupiter, Saturn, more "

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Explore Neptune's blue color, its strong winds, and why it's the most distant planet in our solar system.

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13 Planets: The Latest View of the Solar System

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13 Planets: The Latest View of the Solar System

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An updated look at our solar system, including information about dwarf planets and the latest discoveries.

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A beautifully illustrated journey through the solar system with Professor Astro Cat as your guide.