Mars Facts

Mars ['märz]

The planet fourth in order from the Sun.

Beautiful view of the planet Mars

Mars is known as “the red planet.” It can be seen with the naked eye from the earth and is actually red in color. No one knows who discovered Mars because it has been known by humans since prehistoric times. Its red color is due to rust in the soil on its surface. It was given the name Mars by the Romans after their god of war who was called Mars. The planet Mars was written about and studied by ancient Egyptians, Romans, Greeks, and the Chinese.

Mars is the fourth planet from the sun and orbits at an average distance of 141,633,260 miles (227,936,640 km) from the sun. Mars is about half the size of Earth. A day on Mars lasts slightly longer than a day on Earth at 24 hours and 37 minutes. A year lasts 687 days - almost 2 Earth years! Learn more about Mars' place in the solar system at these Science Trek sites: Planets, the Sun, and Astronomy.

footprint on the surface of Mars sand red

Mars is dry and dusty. It often has great dust storms that have carved and shaped its surface. The temperatures there can be as hot as 70° F (20° C) or as cold as -225° F (-153°C). Earthquakes, volcanoes, and meteor impacts continuously change the landscape.

Mars may have had an atmosphere and water similar to Earth millions of years ago. Scientists think Mars was once a warmer, wetter planet. They have found evidence of ancient river valley networks, lakebeds, rocks that were shaped in liquid water, and possibly large floods in the past. Today, water on Mars is found in the form of ice sheets just under the surface in the polar regions. Mars has a thin atmosphere made up mostly of carbon dioxide. Clouds from volcanic activity have been seen swirling above Mars' surface.

Olympus Mons alt
Image courtesy of NASA

Mars is home to the largest volcano in the solar system: Olympus Mons, which towers over the surface of Mars to a height of 15 miles. That is three times the height of Mount Everest! Mars also has a huge canyon system, known as Valles Marineris, that is 10 times the size of Earth's Grand Canyon. While the planet can be seen with the naked eye from Earth, the invention of the telescope in 1608 allowed scientists to study the many valleys, canyons, and volcanoes along with huge craters and an enormous bulge in the Mars surface called Tharsis.

Moons of Mars

Phobos and Deimos
Image courtesy of NASA

Mars is orbited by two moons known as Phobos and Deimos. They were discovered in August 1877 by Asaph Hall while he was working at the US Naval Observatory. Hall named the moons for the sons of Ares. Ares was the Greek name for the god of war.

Mars’ moons appear to actually be asteroids much like those in the asteroid belt. They may have come close to Mars and been pulled into its gravity where they began to orbit. They are covered in craters and grooves. Phobos is the larger of the two moons and has a huge crater on its surface. Deimos has a smoother surface and is smaller in size.

Learn more about the moons of Mars.

Water on Mars?

Water probably ran on the surface of Mars at one time. Riverbeds have been found along with rocks that appear to have been rounded by running water. There are also signs of erosion found on Mars' surface. No one knows what happened to all of the water. Some of it may exist in the polar regions which have ice caps that change size as Mars goes through its seasons. Some water may exist under the dusty surface or in ground water. Recently, data from orbiting spacecraft have suggested that there may be a large lake of liquid water under the southern ice sheet.

A Water Ice mMap for Mars
Image courtesy of NASA

All these signs of water are very exciting. Why do we care about water on Mars? On Earth, wherever there is water, there is usually life. Perhaps this is also true of Mars. If water once flowed on Mars, did life exist there too? Is it possible that tiny life forms, such as bacteria, still exist underground?

Life on Mars?

Between 1996 and 2005, NASA (National Aeronautics and Space Administration) was involved in a program to investigate the possibility of life on Mars. It was known as the Mars Surveyor Program and was based on sending spacecraft to orbit, land, and explore Mars for evidence of life. It was discovered that the soil on Mars has similarities to Earth's soil. The discovery of water and additional studies of Mars have given hope to the possibility that life did exist on the Red Planet.

Mars Climate Orbiter
Image courtesy of NASA

Several different types of spacecraft have been sent to Mars over the years. One type, called orbiters, orbit Mars and take pictures as they zoom around the planet. Other spacecraft, called landers, provide photos and information from their landing spots on the surface of Mars. The Mars Exploration Rover Mission uses rovers, which are car-sized propelled laboratories that can drive around to different spots. In July 1997, the first rover, Sojourner, landed on the surface of Mars, delivered by a craft known as Pathfinder. Learn more about Pathfinder and Sojourner.

High-Resolution Self-Portrait by Curiosity Rover Arm Camera
Image courtesy of NASA

NASA has sent three additional rovers to Mars. Two rovers named Opportunity and Spirit landed on Mars in January 2004. Opportunity, although now 15 years old, continues to explore the surface and send back important information. The Curiosity rover landed on Mars in August 2012. Rovers help scientists learn what different parts of Mars are made of so that they can understand more about how its environment has changed over time. Learn more about Opportunity and Curiosity.

Curiosity is equipped with ten special pieces of equipment to measure minerals in the soil, cameras to take pictures, drills for getting below the surface, instruments for measuring the atmosphere and radiation, and a 7-foot robotic arm. Curiosity gathers information to help scientists learn whether Mars once had the ingredients for life, including water and the necessary chemicals. To test that, Curiosity drilled a hole in the bottom of a crater that scientists think was once a lake. The information about the powder drilled from the rock told scientists that this crater had the elements that ancient life would have needed to survive.

The Mars Exploration Program continues. A new spacecraft called Insight, a lander was launched in May 2018. Its purpose is to study the deep interior of Mars and try to increase our knowledge of how the planet was formed. In the near future, the Mars 2020 mission will send a new rover to look directly for signs of past life on Mars and to test a method for getting oxygen out of the atmosphere that will help NASA plan a future mission with human astronauts. NASA's current goal is to send a manned mission to Mars in the 2030's. Keep watching the Red Planet - maybe you'll go there someday!

Mars Science Laboratory Guided Entry at Mars
Image courtesy of NASA

Top 10 Questions

September 2013

Thanks to Todd Barber, Lead Propulsion Engineer, Cassini Mission, Jet Propulsion Laboratory; and Matthew Heverly, Mobility Systems Engineer, Jet Propulsion Laboratory for the answers.

  1. How big is Mars?

    Mars is about half the diameter of Earth. Earth's diameter is roughly 8,000 miles and its circumference is 25,000, so Mars would be about 4,000 miles in diameter. (From Josue at Cynthia Mann Elementary in Boise)

  2. Why is Mars hot when it is far from the sun?

    Mars isn't that hot. It is pretty cold during the daytime and the nighttime. We have a weather station on the rover that sends us a weather report every day. Three hundred fifty seven Mars-days after landing, the high was negative 7 degrees Celsius and the low was negative 76 degrees Celsius (that's 19 and minus 104 degrees Fahrenheit). It's actually really, really cold on Mars and it's challenging for us to design a rover that can survive the cold Martian nights! (From Ellie at Owyhee Harbor Elementary School in Boise)

  3. What causes Mars to be sphere shaped?

    It's essentially the force of gravity and that's why all of the large planets are basically like a sphere. Nature tries to minimize energy. It wants the minimum surface area for a given volume, and that's a sphere. (From Cholle at Owyhee Harbor Elementary School in Boise)

  4. If water were on Mars, could you live on it?

    Mars did have water that we could drink. From our discoveries, the water looked to be really acidic, but the water that Curiosity found looked to be like that found in streams and rivers here on Earth. Because it's no longer there, there's no longer any water on the surface of Mars. As was said earlier, Mars is no longer habitable because of the extremely cold temperatures. (From Bradan at Cynthia Mann Elementary School in Boise)

  5. How hot can Mars get?

    Even though Mars is generally a very cold planet, it can have pleasant temperatures. Four conditions must be met: If Mars is as close as it can get to the sun in its elliptical orbit, if it's about noon, if it's the middle of summer, and finally, if you are on its equator. When those 4 conditions are met, it can get to 75 or 80 degrees Fahrenheit. (From Ike at Cynthia Mann Elementary School in Boise)

  6. How many volcanoes are on Mars?

    We're still trying to map out all of the geological features on Mars, but what we know is that there used to be a lot of volcanoes. Now, however, there are no active volcanoes on Mars. There used to be active volcanoes spewing lava all over the surface of Mars, but not anymore. All those have gone extinct. (From Junior at Cynthia Mann Elementary School in Boise)

  7. How many moons does Mars have?

    Mars only has two moons, one more than we have around Earth. The names of the moons are the Greek words for fear [Phobos] and panic [Deimos], and we believe they are probably captured asteroids. (From Claire at Cynthia Mann Elementary School in Boise)

  8. Does Mars have water?

    With our rover missions, we have found past evidence of water. We have found evidence that there used to be flowing streams and rivers on the surface of Mars. Ice has even been found under the surface. However, we know that water cannot exist on the surface with the conditions that exist today. (From Connor at Owyhee Harbor Elementary School in Boise)

  9. Was there life on Mars?

    We don't know yet. Billions of years ago, Mars was warmer and wetter. We have a lot of evidence that liquid water was on the surface. On Earth, whenever we find water, a source of heat molecules and some organic molecules, life is abundant. Mars seems to be a pretty inviting place, at least billions of years ago, for biology to take hold. We do the rover missions for that very question. (From Dalton at Owyhee Harbor Elementary School in Boise)

  10. Is Mars red because the rocks are made of iron oxide?

    Yes, Mars is red because of iron oxide. It's like good old rust here on Earth. When you have metal in an oxidizing environment, it tends to form the oxides that have the reddish/rust color. (From Kyia at Dalton Elementary School in Dalton Gardens)