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The "Habitable Zone" in our solar system.

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The "Habitable Zone" in our solar system.

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habitable zone in our solar system - Google Search

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How the Earth's Magnetic Field protects us.

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How the Earth's Magnetic Field protects us.

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An illustration of how Earth's magnetic field protects the planet from solar radiation.

Credit: Michael Osadciw/University of Rochester

Earth's magnetic field, which protects the planet from harmful blasts of solar radiation, is much older than scientists had previously thought, researchers say. In fact, this invisible, protective shield likely existed shortly after the planet formed - a finding that could shed light on why Earth is habitable and Mars is not.

Without Earth's magnetic field, solar winds - streams of electrically charged particles that flow from the sun - would strip away the planet's atmosphere and oceans. As such, Earth's magnetic field helped to make life on the planet possible, researchers have said.

The magnetic field is generated by swirling liquid metal in Earth's outer core, and this "geodynamo" requires the release of heat from the planet to drive its churning. Nowadays, this heat flow is aided by plate tectonics - the movement of the plates of rock that make up the planet's exterior - which efficiently lets heat transfer from Earth's interior to its surface. [ 50 Amazing Facts About Planet Earth]

Given the importance of Earth's magnetic field, scientists want to pinpoint when it first developed, which could, in turn, provide clues about how the planet has been able to remain habitable and when plate tectonics began. However, when, exactly, plate tectonics originated is hotly debated, and some researchers argue that the early Earth lacked a magnetic field.

Since 2010, the best estimate of the age of Earth's magnetic field was 3.45 billion years. In comparison, Earth is about 4.6 billion years old.

Now, scientists have found that Earth's magnetic field could be up to 4.2 billion years old - about 750 million years older than had been previously thought.

The researchers investigated magnetically sensitive minerals such as magnetite, a naturally occurring cousin of rust. As molten rock cools, magnetite within it becomes literally set in stone, pointing to the location of Earth's magnetic poles at the moment it froze. As a result, the oldest samples of magnetite can reveal the direction and intensity of Earth's magnetic field at the earliest parts of Earth's history, the researchers said.

The scientists analyzed magnetite samples trapped in tiny, ancient zircon crystals that were collected from the Jack Hills in Western Australia. To detect the magnetic fields, the scientists had to have a special magnetic sensor built that was 10 times more sensitive than other instruments used to make these kinds of measurements.

Isolating the zircons from the surrounding rock was challenging. "Typically, we separate zircons out using high magnetic fields, but we couldn't do that here, since it would destroy what information they had," said John Tarduno, a geophysicist at the University of Rochester in New York and lead author of the new study detailing the findings. "So we had to separate thousands of zircons out by hand, cleaning them in mild acids, which took a huge amount of time," Tarduno told Live Science.

Then, to get reliable measurements, the researchers had to make sure the samples they analyzed never got hot enough after they formed to allow the magnetic information recorded within to reset. The researchers found that the minerals were pointed in a variety of magnetic directions, which suggested the samples were pristine.

"[I]f the magnetic information in the zircons had been erased and re-recorded, the magnetic directions would have all been identical," Tarduno said in a statement.

The intensity of the magnetic fields that the samples recorded suggests the presence of an ancient geodynamo, the researchers said.

These findings likely indicate that Earth had a magnetic field, and plate tectonics, since very early in its history.

"It's surprising, because some of the models of the ancient Earth suggest that a magnetic field or plate tectonics could not have occurred that early," Tarduno said. "Those models need to be rethought to include potential ways of cooling Earth's interior early on."

This ancient magnetic field could be a key reason Earth is still habitable and Mars was unable to sustain life, as far as we currently know.

"The oldest previously known magnetic field from a terrestrial planet was on Mars, which was older than 4 billion years old," Tarduno said. "But then, sometime after 4 billion years ago, it died off. If you compare the evolution of Earth and Mars, Mars had a more dense atmosphere, and water, but it probably lost both to erosion from the solar wind because it didn't have a magnetic field to protect them, whereas Earth always appeared to have had a strong magnetic shield."

The scientists detailed their findings in the July 31 issue of the journal Science.

Follow us @livescience, Facebook & Google+. Original article on Live Science.

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Charles Q. Choi, Live Science Contributor

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'Magnetic' Discovery May Reveal Why Earth Supports Life and Mars Doesn't

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Earth's magnetic field, which protects the planet from harmful blasts of solar radiation, is much older than scientists had previously thought, researchers say. In fact, this invisible, protective shield likely existed shortly after the planet formed - a finding that could shed light on why Earth is habitable and Mars is not.

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Venus has the distinction of being the hottest planet in the solar system, and the fault lies solely with its atmosphere. What is it about the air on Venus that keeps the planet cooking?

Atmospheric makeup

The atmosphere of Venus is made up almost completely of carbon dioxide. It also includes small doses of nitrogen and clouds of sulfuric acid. The air of Venus is so dense that by mass, the small traces of nitrogen are four times the amount found on Earth, although nitrogen makes up more than three-fourths of the terrestrial atmosphere. This composition causes a runaway greenhouse effect that heats the planet even hotter than the surface of Mercury, although Venus lies farther from the sun. When the rocky core of Venus formed, it captured much of the gas gravitationally.

In addition to warming the planet, the heavy clouds shield it, preventing visible observations of the surface and protecting it from bombardment by all but the largest meteorites. [ 10 Weirdest Facts About Venus]

Although Venus and Earth are similar in size, someone standing on the ground on Venus would experience air about 90 times heavier than Earth's atmosphere; pressures are similar to diving 3,000 feet beneath the ocean. The most Earth-like atmosphere in the solar system occurs 30 to 40 miles (50 to 60 kilometers) above the surface of Venus. Both oxygen and hydrogen rise above the heavier gas layer covering the ground, and the pressures are similar to our planet.
Chemical composition:

Carbon dioxide: 96 percent

Nitrogen: 3.5 percent

Carbon monoxide, argon, sulfur dioxide, and water vapor: less than 1 percent

(Image: © ESA/MPS/DLR/IDA)

Climate and weather

Winds of about 224 mph (360 kph) keep the clouds of Venus in constant motion. Though the planet spins slowly, only once every 243 Earth days, the clouds zip around the top of the planet's atmosphere every four days. But wind speeds drop closer to the surface, where they only move a few miles per hour.

On Earth, seasons change based on the planet's tilt: When a hemisphere is closer to the sun, it experiences warmer temperatures. But on Venus, most of the sun's heat fails to make it through the thick atmosphere. As such, the planet not only doesn't experience significant temperature changes over the course of the year, it also keeps things constant from night to day.

The clouds of Venus appear bright white or yellow. Unlike Jupiter or Saturn, there are no discernable bands or storms visible to the naked eye.
Further reading: This article was updated on Oct. 18, 2018 by Space.com Senior Writer, Meghan Bartels. Have a news tip, correction or comment? Let us know at community@space.com.

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Venus' Atmosphere: Composition, Climate and Weather

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Venus has the distinction of being the hottest planet in the solar system, and the fault lies solely with its atmosphere. What is it about the air on Venus that keeps the planet cooking? The atmosphere of Venus is made up almost completely of carbon dioxide.

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Mars’ Atmosphere: Composition, Climate & Weather

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Mars’ atmosphere is over 100 times thinner than Earth’s.

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Whenever astronomers announce the discovery of an "Earth-like planet," they're usually talking about planets with roughly Earth-like gravity that are close enough to their star to be warm but not hot and that may (or may not) have liquid water. But there's a whole lot beyond those three must-have ingredients that makes Earth special. Here's an (incomplete) roundup:

The moon: The Earth has a slight tilt and teeters like a top as it spins, which can cause drastic shifts in climate over the course of thousands of years. But because of the moon's stabilizing effect on our orbit, our climate is a lot more stable. Plus, the moon causes the tides, and some biologists think life began in tidal pools.

Stable rotation: There's no reason to think that a planet without a stable rotation would be completely inhabitable (actually, some people think such "eyeball planets" could be our best bet for aliens), but the regularity and frequency of day and night on this planet go far to prevent extreme temperatures and encourage life.

A magnetic field: Our planet is blessed with a strong, stable magnetic field, which staves off the cosmic rays and solar flares that would otherwise fry the planet every now and then. It's also tied up with the next must-have feature on the list ...

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9 Things That Make Earth the Perfect Place for Life

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It's not too surprising that the Earth is so hospitable to life - we would never have evolved enough to wonder about it if it weren't. But when you start to look at all of the things that have come together in just the perfect way to support plants and animals, it gets a little mind-boggling.

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(Image credit: Terry Virts/NASA)

Earth's atmosphere is a thin band of air made up of numerous layers based on temperature.

Without this protective blanket, life on Earth would not exist as it protects us from heat and radiation emitted from the sun and contains the air we breathe.

Though oxygen is crucial for life on Earth, it is not the primary component of our atmosphere. According to education site Vision Learning Earth's atmosphere is composed of approximately 78 percent nitrogen, 21 percent oxygen, 0.93 percent Argon, 0.04 percent carbon dioxide as well as trace amounts of neon, helium, methane, krypton, ozone and hydrogen, as well as water vapor.

But just how high does Earth's atmosphere extend? Well, that depends on who you ask! According to NASA the upper layer of Earth's atmosphere - the exosphere - extends up to 6,200 miles (10,000 km), above which the atmosphere and space blend. Though not everyone agrees where space actually begins, most scientists agree that the Kármán line, situated 62 miles (100 km) above sea level, marks the transition point between Earth and space. Since 99.99997 percent of Earth's atmosphere is located below this point, it's considered a reasonable height to draw the boundary between Earth and space.
Related: Earth's layers: Exploring our planet inside and out
Earth atmosphere layers

(Image credit: Future)

Earth's atmosphere consists of five main layers from lowest to highest: troposphere, stratosphere, mesosphere, thermosphere and exosphere.

The layers are separated based on temperature according to the National Institute of Water and Atmospheric Research (NIWA).The atmosphere thins out in each higher layer until the gases dissipate in space. Air pressure decreases with altitude. At sea level, air pressure is about 14.7 pounds per square inch (1 kilogram per square centimeter), and the atmosphere is relatively dense. At 10,000 feet (3 km), the air pressure is 10 pounds per square inch (0.7 kg per square cm), which means molecules of gas that make up the atmosphere are less dense. That makes it harder for a person to breathe and get enough oxygen to live, although there is evidence for microbial life high up in the clouds.

Troposphere

The troposphere is the lowest and densest layer of the atmosphere and according to NIWA, approximately 75% of all the air in the atmosphere is found in this layer. The troposphere extends from Earth's surface to approximately 5 to 9 miles (8 to 14.5 km) high.

According to NASA, "Tropos" means change, and this atmospheric layer lives up to its name. Gases are constantly mixing in the troposphere and most of Earth's weather is found here. According to educational website CK-12, turbulence in the troposphere is created when the sun warms the Earth's surface, warming the air above. The warm air rises and then expands (due to the lower air pressure) and cools. The cool air sinks forming high pressure systems. According to WorldAtlas most helicopters and light airplanes fly in the troposphere.

Stratosphere

The stratosphere is the second layer of Earth's atmosphere. The stratosphere begins above the troposphere and extends approximately 31 miles (50 km) high. According to NIWA, most of the ozone found in Earth's atmosphere is in the stratosphere. Ozone protects us by absorbing harmful UV rays from the sun. The absorption of UV radiation heats up the stratosphere and temperatures in this layer actually increase with height. According to Weather.gov temperatures in the stratosphere range from approximately -60 degrees Fahrenheit (-51 degrees Celsius) at the bottom to 5 degrees F (-15 degrees C) at the top. Commercial airplanes tend to fly in the lower stratosphere so as to avoid the weather systems in the troposphere, according to aviation education site Aero Corner.

Mesosphere

The mesosphere is the third layer of Earth's atmosphere. According to NASA the mesosphere begins just above the stratosphere and extends to approximately 53 miles (85 km) high.

The top of the mesosphere, called the mesopause, is the coldest part of Earth's atmosphere, with temperatures averaging about minus 130 degrees F (minus 90 degrees C) according to the National Center for Atmospheric Research. The mesosphere is tricky to analyze as jets and balloons don't go high enough but satellites fly too high to directly study the layer. We do however know that most meteors burn up in this layer, and high-clouds known as noctilucent clouds (also known as polar mesospheric clouds) occasionally form in the mesosphere.

Thermosphere

The fourth layer of Earth's atmosphere is the thermosphere. It begins just above the mesosphere and extends to approximately 372 miles (600 km) high, according to NASA. The thermosphere is another atmospheric layer where temperatures rise with altitude, according to NIWA. The warming is caused by the absorption of ultraviolet light and X-rays emitted from the sun.

The thermosphere is considered part of Earth's atmosphere, but air density is so low that most of this layer is what is normally thought of as outer space. In fact, this is where the space shuttles flew and where the International Space Station orbits Earth.

Exosphere

The exosphere is the highest layer of Earth's atmosphere and extends from the top of the thermosphere approximately 6,200 miles (10,000 km) above Earth's surface according to NASA. The exosphere is composed of particles of hydrogen and helium, that are so widely dispersed they rarely collide.

Ionosphere

The ionosphere is a very active layer of Earth's atmosphere that spans the mesosphere, thermosphere and exosphere, according to NASA. It is not a distinct layer and actually grows and shrinks depending on how much energy it is absorbing from the sun.

We have the ionosphere to thank for the beautiful aurora displays that dance across the night sky. Here, the ions from solar wind collide with atmospheric oxygen and hydrogen molecules, exciting them into higher states of energy. The atoms shed this excess energy by emitting photons of light, which we see as the colorful aurora borealis and aurora australis.

(Image credit: NASA's MODIS instrument (Moderate Resolution Imaging Spectroradiometer).)

What's the difference between weather and climate?

Broadly speaking weather refers to short-term changes in atmospheric conditions whereas climate refers to the average weather conditions of a specific location over an extended period of time according to the United States Geological Survey. The National Oceanic and Atmospheric Administration (NOAA) further describes the difference simply as "climate is what you expect, weather is what you get".

Regional climate is defined by the University Corporation for Atmospheric Research as the average weather in a place over more than 30 years. A region's climate is often described, for example, as sunny, windy, dry, or humid. These can also describe the weather in a certain place, but while the weather can change in just a few hours, climate changes over a longer span of time.
Related: 7 solar system worlds where the weather is crazy
Earth's global climate is an average of regional climates. The global climate has cooled and warmed throughout history. Today, we are seeing unusually rapid warming. The scientific consensus, as stated by the Intergovernmental Panel on Climate Change (IPCC), is that greenhouse gases, which are increasing because of human activities, are trapping heat in the atmosphere.

Earth's atmosphere FAQs answered by an expert

What is Earth's atmosphere made of?

How high does Earth's atmosphere go?

(Image credit: NASA)

Are there different layers in Earth's atmosphere?

What would happen if Earth's atmosphere disappeared?

We asked Fangqun Yu a few frequently asked questions about Earth's atmosphere.

Atmospheric difference: Earth, Venus and Mars

To better understand the formation and composition of Earth, scientists sometimes compare our planet with Venus and Mars. All three of these planets are rocky in nature and are part of the inner solar system, meaning that they are in between the sun and the asteroid belt.

Venus' atmosphere is almost entirely composed of carbon dioxide. The entire planet is shrouded in thick toxic sulfuric acid clouds that trap heat, resulting in what is known as a runaway greenhouse effect. As such, Venus is the hottest planet in the solar system despite being the second closest planet to the sun.e. Spacecraft have to be heavily reinforced to survive the crushing pressure (90 times heavier than Earth), and the oven-like surface temperatures (900 Fahrenheit or 475 Celsius) hot enough to melt lead, according to NASA . s that Venus has no significant seasonal temperature changes.

Mars' atmosphere is also mostly composed of carbon dioxide, with traces of nitrogen, argon, oxygen, carbon monoxide and some other gases. The Red Planet's atmosphere is about 100 times thinner than Earth's - a very different situation from the ancient past, when geological evidence shows that Mars used to be much wetter and warmer billions of years ago, according to NASA. S. If you were to stand on Mars and look to the sky, you'd be greeted with a red hue caused by dust particles suspended in the air, rather than the blue skies we see here on Earth. Due to Mars' thin atmosphere, heat from the sun quickly escapes the planet. According to NASA, if you stood on the Martian equator at noon, your feet would experience a toasty 75 degrees Fahrenheit (24 degrees Celsius) though temperatures at your head would be rather chilly at around 32 degrees Fahrenheit (0 degrees Celsius).

Scientists routinely compare small, rocky exoplanets to Earth, Venus and Mars to get a better sense of their habitability. The routinely accepted definition of "habitability" is that a planet is close enough to the star for liquid water to exist on its surface. Too far, and the water turns icy; too close, and the water evaporates. However, habitability not only depends on the star-planet distance, but also the planet's atmosphere, the star's variability, and other factors.

Additional resources

You can explore the ionosphere in more detail with the National Weather Service and learn more about the historic increase in atmospheric carbon dioxide from Climate.gov. If you fancy reading about the fascinating world of the atmospheric microbiome then check out this interesting article in Scientific American.

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Earth's atmosphere: Facts about our planet's protective blanket

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Earth's atmosphere protects the planet in more ways than one. This thin band of air is unique to Earth, and we wouldn't exist without it.

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(Image credit: NASA/JPL-Caltech/Univ. of Arizona)

Liquid water may still flow on Mars, but that doesn't mean it's easy to spot. The search for water on the Red Planet has taken more than 15 years to turn up definitive signs that liquid flows on the surface today. In the past, however, rivers and oceans may have covered the land. Where did all of the liquid water go? Why? How much of it still remains?

Observations of the Red Planet indicate that rivers and oceans may have been prominent features in its early history. Billions of years ago, Mars was a warm and wet world that could have supported microbial life in some regions. But the planet is smaller than Earth, with less gravity and a thinner atmosphere. Over time, as liquid water evaporated, more and more of it escaped into space, allowing less to fall back to the surface of the planet.

Where is the water today?

Liquid water appears to flow from some steep, relatively warm slopes on the Martian surface. Features known as recurring slope lineae (RSL) were first identified in 2011in images taken by the High Resolution Imaging Science Experiment (HiRISE) camera aboard the Mars Reconnaissance Orbiter (MRO). The dark streaks, which appear seasonally, were confirmed to be signs of salty water running on the surface of the planet.

"If this is correct, then RSL on Mars may represent the surface expression of a far more significant ongoing drainage system on steep slopes in the mid-latitudes," a research team member told Space.com in 2012.

In 2015, spectral analysis of RSL led scientists to conclude they are caused by salty liquid water. [Related: Salty Water Flows on Mars Today, Boosting Odds for Life]

"The detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks," the study's lead author, Lujendra Ojha, of the Georgia Institute of Technology in Atlanta, said in a statement. Vast deposits of water appear to be trapped within the ice caps at the north and south poles of the planet. Each summer, as temperatures increase, the caps shrink slightly as their contents skip straight from solid to gas form, but in the winter, cooler temperatures cause them to grow to latitudes as low as 45 degrees, or halfway to the equator. The caps are an average of 2 miles (3 kilometers) thick and, if completely melted, could cover the Martian surface with about 18 feet (5.6 meters) of water.

Frozen water also lies beneath the surface. Scientists discovered a slab of ice as large as California and Texas combined in the region between the equator and north pole of the Red Planet. The presence of subsurface water has long been suspected but required the appearance of strange layered craters to confirm. Other regions of the planet may contain frozen water, as well. Some high-latitude regions seem to boast patterned ground-shapes that may have formed as permafrost in the soil freezes and thaws over time.

The European Space Agency's Mars Express spacecraft captured images of sheets of ice in the cooler, shadowed bottoms of craters, which suggests that liquid water can pool under appropriate conditions. Other craters identified by NASA's Mars Reconnaissance Orbiter show similar pooling.

Evidence for water on Mars first came to light in 2000, with the appearance of gullies that suggested a liquid origin. Their formation has been hotly debated over the ensuing years.

But not everyone thinks that Mars contains water today. New research reveals that RSL may actually have formed by granular flows formed by the movement of sand and dust.

"We've thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand," lead author Colin Dundas said in a statement. "This new understanding of RLS supports other evidence that shows that Mars today is very dry."

That idea may have been washed away by the recent discovery of a possible subsurface lake near the Martian South Pole.

An underground lake?

Researchers made a big splash when they announced that Mars might be hiding a lake beneath its southern pole. The European Mars Express spacecraft used its Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) to detect the proposed water. Ground-penetrating radar sent radar pulses to the surface, then timed how long it took for them to be reflected. The properties of the subsurface layers affect how long it takes for the beams to return.

MARSIS' investigation revealed that the Martian south pole is composed of multiple layers of ice and dust to a depth of about nearly 1 mile (1.5 kilometers) spread over a 124-mile-wide (200 km) region.

"This subsurface anomaly on Mars has radar properties matching water or water-rich sediments," Roberto Orosei, principal investigator of the MARSIS experiment and lead author of the new research, said in a statement.

MARSIS also revealed the presence of a subsurface lake among the pockets. According to the radar echoes, the lake is no more than 12.5 miles (20 km) across, buried nearly a mile beneath the surface. The scientists aren't certain of the lake's depth, but they have confirmed that it is at least 3 feet (1 meter) deep. According to the researchers, the lake must have salt to keep from freezing.

"This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered," Orosei said.

Not all researchers are as certain about the presence of liquid water.

"I think it's a very, very persuasive argument, but it's not a conclusive or definitive argument," Steve Clifford, a Mars researcher at the Planetary Science Institute in Arizona, told Space.com. "There's always the possibility that conditions that we haven't foreseen exist at the base of the cap and are responsible for this bright reflection."

More than three decades ago, Clifford proposed that Mars could harbor liquid water beneath its polar caps in the same way that Earth does. On Earth, lakes beneath the Antarctic and Greenland ice sheets are created when heat from within the planets melt the glaciers in patches. Clifford told Space.com that a similar scenario could happen beneath the Martian polar ice caps.

"The bright spot seen in the MARSIS data is an unusual feature and extremely intriguing," Jim Green, NASA's chief scientist, said in a statement. "It definitely warrants further study. Additional lines of evidence should be pursued to test the interpretation."

"We hope to use other instruments to study it further in the future," Green said.

(Image credit: NASA/JPL-Caltech/University of Arizona [Full Story])

Searching for an oasis

When Mariner 9 became the first craft to orbit another planet in 1971, the photographs it returned of dry river beds and canyons seemed to indicate that water had once existed on the Martian surface. Images from the Viking orbiters only strengthened the idea that many of the landforms may have been created by running water. Data from the Viking landers pointed to the presence of water beneath the surface, but the experiments were deemed inconclusive. [ Mars Explored: Landers and Rovers Since 1971 (Infographic)]

The early '90s kicked off a slew of Mars missions. Scientists were flooded with a wealth of information about Mars. Three NASA orbiters and one sent by the European Space Agency studied the planet from above, mapping the surface and analyzing the minerals below. Some detected the presence of minerals, indicating the presence of water. Other data measured enough subsurface ice to fill Lake Michigan twice. They found evidence that ancient hot springs once existed on the surface and sustained precipitation once fell in some areas. And they found patches of ice within some of the deeper craters.

Impact craters offer a view of the interior of the red planet. Using the ESA's Mars Express and NASA's Mars Reconnaissance Orbiter, scientists were able to study rocks ejected from the planet's interior, finding minerals that suggested the presence of water.

"Water circulation occurred several kilometers deep in the crust some 3.7 billion years ago," Nicolas Mangold, of the University of Nantes in France, said in a statement.

But orbiters weren't the only objects launched toward Mars. NASA's Curiosity rover is the fifth robot to land on the surface of the Red Planet in the last 15 years. Pathfinder, Phoenix, Spirit and Opportunity all took detailed measurements of the planet; all but Phoenix traveled across the surface collecting a treasure trove of information.

(Image credit: Renno, et al., NASA)

The probes dug into the ground, examining rocks and performing experiments. In 2008, Phoenix turned up small chunks of bright material that disappeared after four days, leading scientists to surmise that they were pieces of water ice. The lander went on to detect water vapor in a sample it collected and analyzed, confirming the presence of frozen water on the red planet.

Spirit and Opportunity, the twin rovers, found traces of water enclosed in rock. In a shining example of a problem becoming a solution, a broken wheel on Spirit scraped into the top of the Martian surface, revealing a layer beneath rich in silica that had most likely formed in the presence of water.

Curiosity has found yet more evidence of water flowing on ancient Mars. The 1-ton rover rolled through an ancient stream bed shortly after touching down in August 2012, and it has examined a number of rocks that were exposed to liquid water billions of years ago.

Mars missions aren't the only way to search for water on Mars. Scientists studying rocks ejected from the Red Planet found signs that water lay beneath the surface in the past.

"While robotic missions to Mars continue to shed light on the planet's history, the only samples from Mars available for study on Earth are Martian meteorites," lead author Lauren White, of the JPL, said in a statement.

"On Earth, we can utilize multiple analytical techniques to take a more in-depth look at meteorites and shed light on the history of Mars."

Historical landforms

In addition to examining the relatively recent (geologically speaking) presence of water, the various missions have also studied the surface of the planet in a historical context. The river beds of Mars don't run wet today, but scientists can study them to learn more about the evolution of the planet. [ Photos: The Search for Water on Mars]

The flatter northern plains of Mars may once have hosted an ocean, or possibly, as the planet cycled through dry periods, two. The more recent body of water would likely have only been temporary, seeping into the ground, evaporating, or freezing in less than a million years, scientists say.

Riverbeds and gullies indicate that water ran, at least briefly, across the surface of Mars. A hundred times more water may have flowed annually through a large channel system known as Marte Vallis than passes through the Mississippi River each year, according to estimates. The gullies themselves are smaller, likely forming during brief torrential rainstorms when fast-moving water could have carved them across the land.

Curiosity found indications that at least one region of Mars, Mount Sharp, was built by sediments deposited in a lake bed millions of years ago, suggesting large pools existed on the planet for significant time periods.

"If our hypothesis for Mount Sharp holds up, it challenges the notion that warm and wet conditions were transient, local, or only underground on Mars," Curiosity deputy project scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory (JPL) said in a statement.

On Earth, the land around rivers and lakes is wetter, made up of mud and clays. Such deposits exist on Mars as well, trapping water and indicating where larger bodies may have once existed.

Water on Mars may be doing something more than sitting pretty. A new study reveals that when the liquid boils, thanks to low pressures, it can make the sand levitate.

"Sediment levitation must therefore be considered when evaluating the formation of recent and present-day Martian mass wasting features, as much less water may be required to form such features than previously thought," the researchers wrote in their study, which was published in the journal Nature Communications.

Liquid gold

Water may seem like a very common element to those of us stuck on Earth, but it has great value. In addition to understanding how Mars may have changed and developed over time, scientists hope that finding water will help them to find something even more valuable - life, either past or present.

Only Earth is known to host life, and life on our planet requires water. Though life could conceivably evolve without relying on this precious liquid, scientists can only work with what they know. Thus they hope that locating water on celestial bodies such as Mars will lead to finding evidence for life.

With this in mind, NASA developed a strategy for exploring the Red Planet that takes as its mantra "follow the water." Recent orbiters, landers and rovers sent to Mars were designed to search for water, rather than life, in the hopes of finding environments where life could have thrived.

That has changed, however, with the flood of evidence these robots have returned. Curiosity determined that Mars could indeed have supported microbial life in the ancient past, and the next NASA rover - a car-size robot based heavily on Curiosity's basic design - will blast off in 2020 to look for evidence of past Red Planet life.
Additional resources Follow Nola Taylor Redd at @NolaTRedd, Facebook or Google+. Follow us at @Spacedotcom, Facebook or Google+.

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(Image credit: NASA/JPL-Caltech/Univ. of Arizona) Liquid water may still flow on Mars, but that doesn't mean it's easy to spot. The search for water on the Red Planet has taken more than 15 years to turn up definitive signs that liquid flows on the surface today.

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(Image credit: NASA Goddard's Scientific Visualization Studio)

Based on NOAA's temperature data, 2020 was the second warmest year ever recorded, just behind 2016. In the 21st century, average yearly temperature on has been more than 2 degrees F (more than 1 degree C) higher than recorded pre-industrial temperatures.

Earth is the only planet we know of that can support life. The planet has two major advantages that keep it habitable: its distance from the sun, and its protective atmosphere.

Earth lies in a "Goldilocks zone" that is not too far from the sun, but not too close either. The distance from Earth to the sun is one of the most important factors in making Earth habitable. Much closer, and seas would boil: temperatures on Venus, the next closest planet to the sun, reach more than 880 degrees Fahrenheit (471 degrees Celsius), Space.com previously reported. While the closest planet to the sun, , doesn't trap heat like Venus, its surface can still top 840 degrees Fahrenheit (450 degrees Celsius). Meanwhile, one planet farther from the sun, the average temperature on Mars is minus 80 degrees F (minus 60 degrees C).

In addition, Earth's atmosphere plays a vital role in regulating the temperature. The atmosphere provides a blanket of gases that not only protects us from excessive heat and harmful radiation from the sun, but also traps heat rising from the Earth's interior. Over the past few hundred years, the planet's atmosphere has been altered by human industrialization, changing the way it traps and releases heat.

Measuring global temperature

To estimate the global temperature, researchers measure air temperatures on land and at sea at thousands of observation stations around the world, day in and day out. Then, they add all those measurements up and divide the result by the number of observations taken - that gets them an average air temperature for the whole globe.

For example, NOAA reported in a press release (opens in new tab) that 2020 was the second-warmest year on record, in agreement with the United Kingdom Met Office, while measurements from NASA (opens in new tab) and the European Union's Earth observation agency Copernicus ranked it as tied with 2016 for the top spot.

Temperatures are less useful for climate researchers than temperature anomalies, so most temperature reports use temperature anomalies: the difference between current temperature and a historical average.

NASA's Goddard Institute for Space Studies (GISS) assumes that temperature anomalies are about the same up to about 1,200 kilometers from a station. That method means they can estimate temperatures using a smaller number of stations, especially in the polar regions. NOAA, on the other hand, uses different areas, and produces a more conservative estimate.

NOAA tracks anomalies relative to temperatures between 1901 and 2000. According to NOAA's data, average anomalies calculated for 2020 were 1.76 degrees F (0.98 degrees C) higher than the average temperatures for all the years in the 20th century.

What are the most extreme temperatures on Earth?

According to the World Meteorological Organization (opens in new tab), the coldest temperature measured on Earth was at Vostok Station in Antarctica, where it reached minus 128.6 degrees F (minus 89.2 degrees C) on July 21, 1983. The coldest inhabited place is Oymyakon, Russia, a small village in Siberia, where it dips down to an average of minus 49 F (minus 45 degrees C) and once hit a low of minus 96.16 F (minus 71 degrees C).

The hottest temperature currently recognized was recorded at Greenland Ranch (Furnace Creek) in Death Valley, Calif., where it reached 134 F (56.7 C) on July 10, 1913. But even that distinction depends on what is being measured. Death Valley's record is for the highest air temperature. A higher surface temperature of 159.3 F (70.7 C) was recorded by a Landsat satellite in 2005 in the Lut Desert in Iran, according to a 2021 paper published in the journal Bulletin of the American Meteorological Society (opens in new tab). The paper suggests that the recorded temperature might even be an underestimate.

Temperature extremes by continent

This chart shows the temperature records for each continent - the highest and lowest temperatures recorded in North America, South America, Europe, Asia, Africa and Antarctica. These records are kept by the World Meteorological Association, which divides continents using its own regions. Those divisions include Greenland and some of the Middle East as part of Europe, for example, but other countries in the Middle East are considered part of Asia.

How is the Earth's temperature changing?

The National Oceanic and Atmospheric Administration (NOAA) reported average surface temperatures on Earth rose, on average, 1.71 degrees Fahrenheit (0.95 degrees Celsius) between 1880 and 2016. The average rise has been accelerating in recent years, and the Earth's atmosphere now traps twice as much heat as it did in 2005 due to human industrialization and fossil fuel consumption.

In 2015, 159 nations ratified the Paris Agreement, a commitment to change behavior and consumption to try to halt the warming at 2.7 degrees F (1.5 degrees C) above Earth's average temperature before the Industrial Age. Given industry and transportation reliance on fossil fuels, many studies suggest that agreement will be difficult to keep to.

In fact, we have likely already committed the planet to warming past the Paris Agreement target, Space.com previously reported.

Global warming is now included in larger discussions of "climate change." The planet's average temperature is rising - some areas are seeing even faster warming temperatures, like Europe and the Arctic - but as the temperature rises and the planet traps more heat, wrote (opens in new tab), that process also prompts sea level rise, glacier and ice sheet melting, and even changes in growing seasons for wildlife and crops. Climate change and global warming make hurricanes stronger, and can prompt drought and heat waves in some places while worsening floods in others.

A rise of a few degrees in temperature may not seem like much, but according to NASA, during the last ice age when northeastern North America was covered by more than 3,000 feet of ice, the global average temperature was only 5 to 9 degrees cooler than it is today.

Additional resources

If you want to know more about Earth at different average temperatures through its history, check out this feature from News from Science (opens in new tab) about the Smithsonian Museum of Natural History's updated fossil hall - or (opens in new tab) the hall yourself!

For books on Earth's temperature, climate change and the future of life on Earth, try Mary Robinson's 2018 book Climate Justice (opens in new tab), or All We Can Save (opens in new tab), a 2020 collection of essays edited by Ayana Elizabeth Johnson and Katharine K. Wilkinson.

Bibliography

Zhao, Yunxia, Hamid Norouzi, Marzi Azarderakhsh, and Amir AghaKouchak. "Global Patterns of Hottest, Coldest, and Extreme Diurnal Variability on Earth." Bulletin of the American Meteorological Society 102, no. 9 (September 1, 2021): E1672-81. https://doi.org/10.1175/BAMS-D-20-0325.1 (opens in new tab).

Tim Sharp is the Reference Editor for Space.com. He manages articles that explain scientific concepts, describe natural phenomena and define technical terms. Previously, he was a Technology Editor at The New York Times and the Online Editor at the Des Moines Register. He was also a copy editor at several newspapers. Before joining Purch, Tim was a developmental editor at the Hazelden Foundation. He has a journalism degree from the University of Kansas. Follow Tim on Google+ and @therealtimsharp

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(Image credit: NASA Goddard's Scientific Visualization Studio) Based on NOAA's temperature data, 2020 was the second warmest year ever recorded, just behind 2016. In the 21st century, average yearly temperature on has been more than 2 degrees F (more than 1 degree C) higher than recorded pre-industrial temperatures.

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How much water is there on, in, and above the Earth?
All Earth's water, liquid fresh water, and water in lakes and rivers
The Earth is a watery place. But just how much water exists on, in, and above our planet? About 71 percent of the Earth's surface is water-covered, and the hold about 96.5 percent of all Earth's water. Water also exists in the air as water vapor, in and , in icecaps and , in the ground as soil moisture and in , and even in you and your dog.

Water is never sitting still. Thanks to the water cycle, our planet's water supply is constantly moving from one place to another and from one form to another. Things would get pretty stale without the water cycle!

All Earth's water in a bubble

The globe illustration shows blue spheres representing relative amounts of Earth's water in comparison to the size of the Earth. Are you surprised that these water spheres look so small? They are only small in relation to the size of the Earth. This image attempts to show three dimensions, so each sphere represents "volume." The volume of the largest sphere, representing all water on, in, and above the Earth, would be about 332,500,000 cubic miles (mi ³) (1,386,000,000 cubic kilometers (km ³)), and be about 860 miles (about 1,385 kilometers) in diameter.

The smaller sphere over Kentucky represents Earth's liquid fresh water in groundwater, swamp water, rivers, and lakes. The volume of this sphere would be about 2,551,000 mi ³(10,633,450 km ³) and form a sphere about 169.5 miles (272.8 kilometers) in diameter. Yes, all of this water is fresh water, which we all need every day, but much of it is deep in the ground, unavailable to humans.

Do you notice the "tiny" bubble over Atlanta, Georgia? That one represents fresh water in all the lakes and rivers on the planet. Most of the water people and life on earth need every day comes from these surface-water sources. The volume of this sphere is about 22,339 mi ³ (93,113 km ³). The diameter of this sphere is about 34.9 miles (56.2 kilometers). Yes, Lake Michigan looks way bigger than this sphere, but you have to try to imagine a bubble almost 35 miles high-whereas the average depth of Lake Michigan is less than 300 feet (91 meters).

Water is on and in the Earth

The vast majority of water on the Earth's surface, over 96 percent, is water in the oceans. The freshwater resources, such as water falling from the skies and moving into streams, rivers, lakes, and groundwater, provide people with the water they need every day to live. Water sitting on the surface of the Earth is easy to visualize, and your view of the water cycle might be that rainfall fills up the and . But, the unseen water below our feet is critically important to life, also. How do you account for the flow in rivers after weeks without rain? In fact, how do you account for the water flowing down a driveway on a day when it didn't rain? The answer is that there is more to our water supply than just surface water, there is also plenty of water beneath our feet.

Even though you may only notice water on the Earth's surface, there is much more freshwater stored in the ground than there is in liquid form on the surface. In fact, some of the water you see flowing in rivers comes from seepage of groundwater into river beds. Water from precipitation continually seeps into the ground to recharge , while at the same time water in the ground continually recharges rivers through seepage.

Humans are happy this happens because we make use of both kinds of water. In the United States in 2010, we used about 275 billion gallons (1,041 billion liters) of surface water per day,and about 79.3 billion gallons (300.2 billion liters) of groundwater per day. Although surface water is used more to supply drinking water and to irrigate crops, groundwater is vital in that it not only helps to keep rivers and lakes full, it also provides water for people in places where visible water is scarce, such as in desert towns of the western United States. Without groundwater, people would be sand-surfing in Palm Springs, California instead of playing golf.

How much water is there on (and in) the Earth? Here are some numbers you can think about:

If all of Earth's water (oceans, icecaps and glaciers, lakes, rivers, groundwater, and water in the atmosphere was put into a sphere, then the diameter of that water ball would be about 860 miles (about 1,385 kilometers), a bit more than the distance between Salt Lake City, Utah to Topeka, Kansas. The volume of all water would be about 332.5 million cubic miles (mi³), or 1,386 million cubic kilometers (km³). A cubic mile of water equals more than 1.1 trillion gallons. A cubic kilometer of water equals about 264 billion gallons (1 trillion liters).

About 3,100 mi³ (12,900 km³) of water, mostly in the form of water vapor, is in the atmosphere at any one time. If it all fell as precipitation at once, the Earth would be covered with only about 1 inch of water.

The 48 contiguous (lower 48 states) United States receives a total volume of about 4 mi³ (17.7 km³) of precipitation each day.

Each day, 280 mi³ (1,170 km³)of water evaporate or transpire into the atmosphere.

If all of the world's water was poured on the contiguous United States, it would cover the land to a depth of about 107 miles (145 kilometers).

Of the freshwater on Earth, much more is stored in the ground than is available in rivers and lakes. More than 2,000,000 mi³ (8,400,000 km³) of freshwater is stored in the Earth, most within one-half mile of the surface. But, if you really want to find freshwater, most is stored in the 7,000,000 mi³ (29,200,000 km³) of water found in glaciers and icecaps, mainly in the polar regions and in Greenland.

Where is Earth's water located?

For a detailed explanation of where Earth's water is, look at the data table below. Notice how of the world's total water supply of about 332.5 million mi ³ of water, over 96 percent is saline. Of total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of freshwater is in the ground. Rivers are the source of most of the fresh surface water people use, but they only constitute about 509 mi ³ (2,120 km ³), about 1/10,000 th of one percent of total water.
Note: Percentages may not sum to 100 percent due to rounding.
One estimate of global water distribution Source: Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), 1993, Water in Crisis: A Guide to the World's Fresh Water Resources (Oxford University Press, New York). Sources and more information:
(Percents are rounded, so will not add to 100)

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All Earth's water, liquid fresh water, and water in lakes and rivers The Earth is a watery place. But just how much water exists on, in, and above our planet? About 71 percent of the Earth's surface is water-covered, and the hold about 96.5 percent of all Earth's water.

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Although it is the second planet from the sun, Venus is the hottest planet in the solar system. The reason Venus is hotter than even Mercury is not because of its position in the solar system but because of its thick, dense cloud layer.

(Image credit: ESA/MPS/DLR/IDA VIRTIS infrared image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA)

A warm blanket
Venus is the planet most similar to the Earth in terms of size and mass, but its atmosphere causes huge differences in the temperatures of the two planets. The distance to Venus from the sun plays only a small role in the cause of its elevated heat wave.

The atmosphere of Venus is made up almost completely of carbon dioxide, with traces of nitrogen. Much of the hydrogen in the atmosphere evaporated early in the formation of Venus, leaving a thick atmosphere across the planet. At the surface, the atmosphere presses down as hard as water 3,000 feet beneath Earth's ocean.

The average temperature on Venus is 864 degrees Fahrenheit (462 degrees Celsius). Temperature changes slightly traveling through the atmosphere, growing cooler farther away from the surface. Lead would melt on the surface of the planet, where the temperature is around 872 F (467 C).

Temperatures are cooler in the upper atmosphere, ranging from (minus 43 C) to (minus 173 C).
Balmy all year-round
Temperatures on Venus remain consistent over time. For one thing, the planet takes 243 Earth days to spin once on its axis (and it spins backwards, at that; on Venus, the sun rises in the west and sets in the east). The nights on Venus are as warm as the days.

Venus also has a very small tilt of only 3.39 degrees with respect to the sun, compared to 23.4 degrees on Earth. On our planet, it is the tilt that provides us with the change in seasons; the hemisphere slanted closer to the sun feels the heat of spring and summer. The lack of tilt means that even if Venus got rid of its overheated atmosphere, it would still feel fairly consistent temperatures year round.

The lack of significant tilt causes only slight temperature variations from the equator to the poles, as well.
- Nola Taylor Redd, SPACE.com Contributor Related: Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.

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Although it is the second planet from the sun, Venus is the hottest planet in the solar system. The reason Venus is hotter than even Mercury is not because of its position in the solar system but because of its thick, dense cloud layer.