MARS
Mars is the fourth planet from the Sun and the next one out from Earth. People call it the Red Planet, and once you know why, you can spot it in the night sky just by looking for that rusty, pinkish dot. Mars has the tallest volcano anywhere in the solar system, two strange potato-shaped moons, dust storms big enough to swallow an entire country, and a whole crew of robots driving around its surface right now. Here’s what makes Mars one of the most interesting worlds we’ve ever found.
Quick Facts About Mars
| Fact | Value |
|---|---|
| Position | Fourth planet from the Sun |
| Type | Terrestrial (rocky) planet |
| Diameter | 6,791 km (4,219 miles) — about half of Earth’s |
| Distance from Sun | 228 million km (142 million miles) on average |
| Length of day (one “sol”) | 24 hours, 37 minutes |
| Length of year | 687 Earth days |
| Surface temperature | Average -63 °C (-81 °F); range -153 °C to +20 °C |
| Surface air pressure | About 610 pascals (less than 1% of Earth’s) |
| Gravity | 38% of Earth’s |
| Mass | 11% of Earth’s |
| Moons | 2 (Phobos and Deimos) |
| First recorded | Around 2,000 BCE by Egyptian astronomers |
Where Is Mars in the Solar System?
Mars sits in fourth place out from the Sun, right after Earth. Beyond Mars is the asteroid belt, and after that come the gas and ice giants. Mars belongs to a small group of rocky worlds called the terrestrial planets — Mercury, Venus, Earth, and Mars. They all have hard surfaces you could walk on, unlike Jupiter or Saturn, which are basically giant balls of gas.
Even though Mars is one of our nearest planetary neighbors, it isn’t actually close. Sunlight takes about 13 minutes to reach Mars, while it only takes 8 minutes to reach Earth. The distance between Earth and Mars also keeps changing as both planets orbit the Sun. At their closest they’re around 54 million km apart. At their farthest, more than 400 million km — over seven times further away.
How Mars Compares to Earth
If Earth and Mars were twins, Mars would be the smaller one with a serious case of frostbite. Mars is about half the size of Earth, has 38% of Earth’s gravity, and gets only about half as much sunlight. The good news is that the two planets share more than you might think. Mars tilts on its axis at 25°, almost the same angle as Earth’s 23.4°, so Mars has four real seasons. A Mars day is also surprisingly close to ours — just 37 minutes longer. The big difference is the air. Earth’s atmosphere is thick, breathable, and packed with oxygen. Mars’s is thin, mostly carbon dioxide, and would kill you in seconds.
Why Is Mars Called the Red Planet?
The short answer: rust.
Mars’s soil and rocks are full of iron, and over billions of years that iron has reacted with the small amounts of oxygen in Mars’s atmosphere. The result is iron oxide — the same red-brown stuff that grows on a bike left out in the rain. The rusted dust is everywhere on Mars. It coats the rocks, blows around in storms, and gives the planet that famous reddish color when you see it in the sky.
Up close, though, Mars isn’t just one shade of red. NASA’s rovers have sent back photos showing all sorts of colors on the surface — gold, brown, tan, and a few patches of dark gray. The dust just happens to be reddish, and there’s enough of it everywhere to make the planet look uniformly red from far away. Scientists even have a name for the dusty Martian soil: regolith.
The other surprise is the sky. On Mars, the daytime sky is a pinkish, butterscotch color instead of blue, because the fine dust in the air scatters sunlight differently than Earth’s air does. Around sunrise and sunset, though, the sky right around the Sun looks blue — basically the opposite of what we see at home.
Other Names Across History
Mars has been a famous dot in the sky for thousands of years, and almost every ancient civilization noticed its color. The Egyptians called it Her Desher — “the red one.” The Babylonians named it Nergal, after their god of death and disease. The Greeks linked the red dot to Ares, their god of war, and the Romans renamed him Mars. The month of March is named after the same Roman god.
The first person to look at Mars through a telescope was the Italian astronomer Galileo Galilei in 1610. About 250 years later, in 1877, another Italian astronomer named Giovanni Schiaparelli drew Mars with strange long lines on it. He called them canali, meaning channels. People who didn’t speak Italian translated it as “canals” and assumed someone must have built them. We’ll come back to that story.
What Is Mars Made Of? Surface, Volcanoes & Canyons
Mars is a terrestrial planet, which means it has the same basic layers as Earth: a metal core in the middle, a rocky mantle around it, and a thinner crust on the outside. Mars’s core is mostly iron, nickel, and sulfur, and it’s somewhere between 1,500 and 2,100 km wide.
The surface of Mars is split into two halves that don’t really match. The northern hemisphere is mostly smooth, low plains. The southern hemisphere is cratered, bumpy, and higher up — full of mountains, ridges, and impact scars. At the top and bottom of the planet sit the polar ice caps, made of frozen water and frozen carbon dioxide (yes, dry ice).
Mars also has water frozen just under its surface, plus some salty liquid water that flows down crater walls in warmer months. Long ago, Mars was much wetter. Old riverbeds, deltas, and lakebeds are scattered all over the planet, and some surface minerals only form when there’s liquid water. Around 3.5 billion years ago, Mars probably looked a lot more like Earth, with rivers, lakes, and possibly oceans covering large parts of it.
Olympus Mons — The Tallest Volcano in the Solar System
Olympus Mons is the biggest volcano on any planet we know of. It stands about 22 km tall, which is nearly three times the height of Mount Everest. Its base is so wide it would cover the U.S. state of Arizona. If you tried to climb it, you wouldn’t really see a mountain. The slopes are so gentle and the volcano is so huge that the curve of Mars itself would hide most of it from your view.
Why is Olympus Mons so massive? Because Mars doesn’t have moving plates of crust like Earth does. On our planet, a hotspot of magma will create a volcano, then the plate it’s on slides away and a new one starts somewhere else. (That’s how Hawaii’s chain of islands formed.) On Mars, the crust stays put, so lava can keep piling up on top of the same spot for billions of years. Olympus Mons last erupted about 25 million years ago, and scientists think it might not be totally dead even now.
Valles Marineris — A Canyon as Long as the United States
If Olympus Mons is the tallest mountain in the solar system, Valles Marineris is the biggest canyon. It stretches for about 4,000 km (2,500 miles) along Mars’s equator, long enough to cross the entire United States from coast to coast. In some places it’s 7 km deep. To put that in perspective, Earth’s Grand Canyon is about 446 km long and 1.8 km deep. Valles Marineris is roughly ten times longer and four times deeper.
Valles Marineris probably formed when Mars’s crust stretched and cracked open billions of years ago, possibly while the giant Tharsis bulge nearby was being pushed up by hot magma. Mars’s biggest impact area, the Borealis Basin, is even larger. It covers around 40% of the planet’s surface and was likely punched in by a huge object the size of Pluto early in Mars’s history.
Mars’s Atmosphere — Thin Air, Big Storms
Mars has air, but not the kind you could survive in. The atmosphere is about 95% carbon dioxide, with a little nitrogen, argon, and only the tiniest bit of oxygen — around 0.16%. Compare that to Earth, where 21% of the air is oxygen. Worse, the whole atmosphere is around 100 times thinner than ours. The pressure on the Martian surface is about 610 pascals; Earth’s is over 100,000 pascals at sea level. If you stood on Mars without a spacesuit, your blood would actually start to bubble.
Mars probably had a much thicker atmosphere a long time ago. Scientists believe it lost most of it about 4 billion years ago, when its protective magnetic field faded away. With nothing to deflect the solar wind, the Sun’s stream of charged particles slowly stripped Mars’s air away into space.
The thin air doesn’t hold heat very well. Mars’s average temperature is about -63 °C (-81 °F), and it can drop as low as -153 °C near the poles in winter. On a sunny summer day at the equator, it can warm up to a chilly 20 °C — but only at your feet. The air is so bad at carrying heat that your head, just a couple of meters higher up, would still feel close to freezing.
What the air is great at is dust. Mars has the biggest dust storms in the solar system. Some grow until they cover the entire planet and last for months. There are also smaller dust devils, which work like tornadoes — tall spinning columns of dust marching across the surface. The Curiosity and Perseverance rovers have caught them on camera plenty of times.
A Day on Mars vs a Year on Mars
A day on Mars is called a “sol.” It lasts 24 hours and 37 minutes. That’s only about 40 minutes longer than a day on Earth, which is one of the stranger coincidences in the solar system — a planet half our size, twice as far from the Sun, and yet it spins at almost exactly the same speed.
A year on Mars is a different story. Mars takes 687 Earth days to go all the way around the Sun, which is nearly two Earth years. If you lived on Mars, you’d only celebrate a birthday roughly every two Earth years. (Make of that what you will.)
The wow stat: Mars day = 24 hours 37 minutes. Mars year = 687 days. Almost the same day as Earth, but a year nearly twice as long.
Mars has four seasons too, because its 25° axial tilt is so close to Earth’s 23.4°. The catch is that the seasons last about twice as long, since the year is twice as long. Spring in Mars’s northern hemisphere is actually the longest season at 194 sols, because Mars’s orbit isn’t a perfect circle. When the planet is closer to the Sun, it moves faster; when it’s farther, it slows down. So spring and summer in the northern hemisphere take longer than autumn and winter.
Phobos and Deimos — Mars’s Two Tiny Moons
Mars has two moons, and they couldn’t be less impressive next to ours. Earth’s moon is over 3,400 km across. Phobos, the bigger of Mars’s two, is only 22 km wide. Deimos is even smaller, about 12 km wide. Both moons are shaped like potatoes, because they’re too small for their own gravity to pull them into a sphere. Most scientists think they’re asteroids that got pulled in by Mars’s gravity a long time ago.
The American astronomer Asaph Hall discovered both moons in 1877, just six days apart. He named them after the Greek god Ares’s two sons. Phobos means “fear” and Deimos means “terror.” (Ares was the Greek version of Mars, so the family stays together.)
Phobos is a strange little moon. It orbits Mars so close — only about 6,000 km above the surface — that it laps the planet three times every Mars day. That makes it the only moon in the solar system that rises in the west and sets in the east, three times in a row, every single day. Phobos is also slowly spiraling closer to Mars. In about 50 million years it’s expected to either crash into the surface or get torn apart by Mars’s gravity. If it breaks up, the pieces could form a thin ring around Mars, making it the second ringed planet in the inner solar system, at least for a while.
Mars has no rings yet, in case you were wondering.
Read more about Phobos and Deimos.
Could Anyone Live on Mars?
Right now? No. Mars is one of the most hostile places we’ve ever set foot on (even with robots). The list of problems is long. The air is unbreathable. The pressure is so low your blood would boil. The surface temperature averages -63 °C. There’s strong radiation hitting the ground because there’s no magnetic field and barely any atmosphere to block it. The dust gets into everything. And the gravity is only 38% of Earth’s, which causes serious health problems for people who stay in low gravity for too long.
But Mars also has some things going for it. There’s water — frozen at the poles, frozen under the ground, and even some salty liquid water that trickles down hillsides in warmer months. In 2018, scientists using radar from a European spacecraft found what looks like a lake of liquid water buried under the south polar ice cap. NASA’s Perseverance rover even carries a tool called MOXIE that has actually made oxygen out of the carbon dioxide in Mars’s air. Future astronauts might be able to use that same trick on a much bigger scale.
So far, no life has been found on Mars. But in 2024, Perseverance drilled a sample from a rock called Cheyava Falls in Jezero Crater that contained chemical patterns which could have been left by ancient microbes. Scientists are being careful with these claims, because there are non-living explanations too. The full answer will probably have to wait until those samples are brought back to Earth as part of the future Mars Sample Return mission.
NASA is aiming to send astronauts to Mars sometime in the 2030s. The trip takes about 7 to 9 months one way, depending on where Earth and Mars are in their orbits.
Exploring Mars — Every Rover, Lander, and Helicopter We’ve Sent
More spacecraft have visited Mars than any other planet besides Earth, and Mars is the only place we’ve ever sent rovers to. Getting there is hard, though. About half of all the missions ever launched to Mars have failed.
Here are the highlights:
- 1965 — Mariner 4. The first spacecraft to fly past Mars. It sent back 22 grainy photos that ended a lot of Martian-civilization theories overnight.
- 1971 — Mariner 9. The first spacecraft to orbit another planet. It mapped most of Mars’s surface and was the mission that revealed Olympus Mons and Valles Marineris.
- 1976 — Viking 1 and 2. The first successful Mars landings. Both landers searched for life and didn’t find any clear signs.
- 1997 — Pathfinder and Sojourner. Sojourner was the first wheeled rover on Mars, about the size of a microwave oven, and it explored for nearly three months.
- 2004 — Spirit and Opportunity. Twin rovers that found strong evidence of past water. Opportunity kept working for over 14 years.
- 2008 — Phoenix. A polar lander that confirmed water ice just below the surface.
- 2012 — Curiosity. A car-sized rover still working today in Gale Crater. It found that Mars used to have lakes and the right chemistry for life.
- 2018 — InSight. A lander that listened for “marsquakes” and mapped Mars’s interior.
- 2021 — Perseverance and Ingenuity. NASA’s newest rover landed in Jezero Crater along with Ingenuity, a small helicopter. Ingenuity made the first powered, controlled flight on another planet, and ended up flying 72 times before retiring in January 2024.
- 2021 — Tianwen-1 and Zhurong. China’s first Mars mission, with a successful rover landing.
- 2024 — Cheyava Falls. Perseverance found a rock that may contain biosignatures, though more study is needed.
The next big step is Mars Sample Return, a NASA and European Space Agency mission that aims to bring the rocks Perseverance is collecting back to Earth in the 2030s. After that, hopefully, the first humans.
Mind-Blowing Wow Facts About Mars
- The Sun looks about half the size from Mars compared to Earth.
- More than 30 confirmed Mars meteorites have been found on Earth, blasted off the surface by ancient asteroid impacts.
- The month of March is named after Mars (because the Roman god of war was honored at the start of the campaigning season).
- Olympus Mons is so tall that its peak pokes up above most of Mars’s atmosphere.
- The Borealis Basin covers roughly 40% of Mars’s surface and may be the biggest impact crater anywhere in the solar system.
- The first powered, controlled flight by an aircraft on another planet happened on April 19, 2021, when NASA’s Ingenuity helicopter lifted off Mars’s surface for 39.1 seconds.
- A NASA experiment called MOXIE has already turned Mars’s carbon dioxide into breathable oxygen — a real first step toward astronauts living there.
- Mars has frost made of carbon dioxide (dry ice), which can grow and shrink with the seasons.
- There are dark, spider-shaped patterns on Mars’s south polar region called araneiform terrain. No spiders involved — just gas escaping from under thawing dry ice.
- We’re currently in Mars Year 38 on the calendar that scientists use to track Martian seasons.
Mars in Stories
People have been telling stories about Mars long before any rover went there. After Schiaparelli’s canali got mistranslated as “canals” in 1877, lots of writers started imagining a Martian civilization. H. G. Wells wrote The War of the Worlds in 1898, about Martians invading Earth. In 1938, Orson Welles read a version of it on the radio so realistically that some listeners thought aliens were actually attacking. Total Recall (1990 and again in 2012) showed people trying to settle a colonized Mars. The Martian (Andy Weir’s 2011 novel and the 2015 film) followed a botanist stranded on the planet, growing potatoes and trying to survive. The TV series The Expanse features Mars as a tough, no-nonsense human colony hundreds of years in the future.
Mars Glossary — Big Words Made Simple
- Sol: a Martian day, 24 hours and 37 minutes long.
- Regolith: the loose, dusty soil covering Mars’s surface.
- Biosignature: a chemical or physical clue that life might once have been present.
- Caldera: the bowl-shaped pit at the top of a volcano.
- Opposition: the moment when Earth lines up between Mars and the Sun. Mars looks biggest and brightest in our sky around opposition, which happens about every 26 months.
- Terrestrial planet: a rocky planet (Mercury, Venus, Earth, or Mars).
- Tharsis bulge: a huge raised area on Mars where its biggest volcanoes sit.
- Retrograde motion: when Mars (or any other planet) appears to move backwards across the sky for a few weeks. It’s an illusion caused by Earth overtaking Mars in its orbit.
Frequently Asked Questions About Mars
Why is Mars called the Red Planet?
Mars looks red because its soil and rocks are full of iron that has rusted over billions of years. The rusty dust covers the whole planet, and when sunlight hits it, the surface reflects back a reddish color.
How big is Mars compared to Earth?
Mars is about half the size of Earth. Its diameter is around 6,791 km, and it has only about 11% of Earth’s mass. If Earth were a tennis ball, Mars would be about the size of a golf ball.
How long is a day on Mars?
A day on Mars is 24 hours and 37 minutes — only 37 minutes longer than a day on Earth. Scientists call one Martian day a “sol.”
How long is a year on Mars?
A year on Mars lasts 687 Earth days, which is almost twice as long as a year on Earth. That’s how long Mars takes to travel once around the Sun.
How many moons does Mars have?
Mars has two moons, Phobos and Deimos. Both are small and shaped like potatoes, and they’re probably captured asteroids.
How tall is Olympus Mons?
Olympus Mons is about 22 km tall — nearly three times the height of Mount Everest. Its base is roughly the size of Arizona, making it the largest known volcano in the solar system.
How cold is Mars?
The average temperature on Mars is about -63 °C. It can range from a chilly 20 °C at the equator on a summer day to -153 °C at the poles in winter.
Can humans breathe on Mars?
No. Mars’s atmosphere is 95% carbon dioxide and only 0.16% oxygen, and it’s about 100 times thinner than Earth’s. Humans would need a sealed spacesuit to survive even a few seconds outside.
Is there life on Mars?
No life has been found yet, but the search continues. In 2024, NASA’s Perseverance rover found a rock called Cheyava Falls with chemical clues that might have been left by ancient microbes. The samples will be studied more carefully on Earth in the future.
How did Mars get its name?
Mars was named after the Roman god of war because its red color reminded ancient people of blood. The Greeks called the same planet Ares, and Mars’s two moons are named after Ares’s sons, Phobos and Deimos.
Learn More About Mars and Other Planets
- Why Is Mars Called the Red Planet?
- Mars vs Earth — Side by Side
- Olympus Mons & Mars’s Surface
- How Long Is a Day on Mars?
- Mars’s Atmosphere & Weather
- Phobos and Deimos — Mars’s Two Tiny Moons
- Mars Rovers — Every Robot That’s Driven the Red Planet
- Could Humans Live on Mars?
- 20 Wow Facts About Mars
- Mars Quiz for Kids
