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Scientists have studied Mars by peering through telescopes, sending robotic spacecraft to orbit the planet, and placing landers and robotic rovers on its surface. Thanks to this exploration, we have learned quite a lot about what Earth and Mars have in common and about what makes each planet unique.
Mars is smaller than earth. The diameter at the of Mars is about half that of the Earth. The of Mars is also about half that of Earth. The volume of Mars is 15% of the volume of Earth. So if you could crack the Earth open like an egg, about 6.5 planets the size of Mars could fit inside.
Mars is not just smaller than Earth, it is also less . Though Mars is 15% of Earth’s volume, it is only 11% of Earth’s . This means that the pull of on the surface of Mars is only 38% as strong as the pull of gravity on Earth’s surface.
Image - Text Version
A colour illustration of Earth and Mars in space. The photo of Mars was taken by the Hubble Space Telescope in 2001.The image of Earth was made from many different satellite images and observations in 2002.
Earth is on the left, blue and swirling with white clouds. Mars is smaller on the right, mostly reddish gold, with some areas of brown and grey, and clumps of white cloud.
If a person were standing on the surface of Mars, their mass would be exactly the same as on Earth, but they wouldn’t weigh the same. This is because is the measurement of the force of gravity on an object. Though the person would contain the same amount of matter, their weight would only be 38% of their weight on Earth. This is because the force of gravity is lower on Mars.
You can calculate your weight on another planet. Check out the “What is your weight on another planet?” activity to try it for yourself.
Two Rocky Planets
Earth and Mars are both rocky planets. They both have similar kinds of iron-rich rocks on their surfaces. Mars is sometimes called the Red Planet. This is because of the red iron oxides or rust on its surface.
Mars has mountains and canyons like Earth, but they can be much bigger. The tallest Martian mountain is called Olympus Mons. It is three times taller than Mount Everest. It is the tallest known mountain in our whole solar system.
Image - Text Version
Shown is a 3D rendering of Olympus Mons.
The surface of the planet is shown as a perfect square of reddish brown landscape on a black background. It is clear this is not a photograph, but a rendering to show topographical features. In the centre of the rendering is a sharp cliff that forms a round, irregular shape. On top of the cliff, three cracks have formed in the surface. This surface rises slightly to a small, shallow, round crater in the centre. The walls of the crater are uneven. The ground around the cliffs is flat with areas of rough texture.
The deepest Martian canyon is called Valles Marineris. It is four times deeper than the Grand Canyon in the United States. Valles Marineris is the deepest known canyon in the solar system.
Mars also has volcanoes but they are not currently active.
Image - Text Version
Shown is a colour photograph of the Curiosity Rover.
The rover is perched at the top of a hill with reddish brown soil and sharp grey rocks. The sky behind is blueish grey with red and gold tones.
There is a camera on a pole on top of the rover, and the lens faces forward. The body of the rover is pale grey brown, and covered with cables, doors, switches and other objects. The rover has six wheels. Three extend from the right side of its body, and three extend from the left, on long mechanical arms. Each arm has a joint that looks a bit like a human elbow. The wheels are dark grey with sharp treads.
Days and Years
Earth rotates around its axis like a spinning top. The time it takes for Earth to complete one full rotation is what we call a day. A day lasts around 24 hours on Earth.
Did you know?
One day on Earth actually lasts 23 hours and 56 minutes, not 24 hours.
Mars spins a bit slower around its axis than Earth, so each day on Mars is a little longer. It lasts 24 hours and 37 minutes. A Martian day is called a sol.
Planets also travel in an orbit around the Sun. This would be like having that spinning top draw an oval path around a point on the floor. The time it takes for Earth to complete one revolution around the Sun is called a year. A year lasts about 365 days on Earth.
Did you know?
One year on Earth actually lasts 365 ¼ days. This is why once every four years we add an extra day at the end of February. This is called a leap year. Having a leap year ensures the calendar stays in sync with the seasons.
Mars has a larger orbit than Earth. Since Mars is further from the Sun, its orbit goes all the way around Earth’s orbit. Mars also moves through the solar system more slowly than Earth. Because of the size and speed of its orbit, a year on Mars lasts 669 sols. This would be 687 Earth days!
Image - Text Version
Shown are two colour illustrations of the Sun, Earth and Mars at two different stages of orbit.
Both illustrations have a black background with the sun represented as a yellow sphere at the centre. Red lines show Mars' orbit, and blue lines show Earth's orbit. Earth's orbit around the sun is drawn as perfect circle. Outside this circle, Mars' orbit is drawn as a larger oval. Earth is shown as a blue sphere and Mars is shown as a red sphere.
In the left illustration, Earth and Mars are close together on the right side of the Sun. This is labelled Opposition: Mars is close and bright.
In the right illustration, Earth is to the right of the Sun, and Mars is to the left of the sun. Because Mars' orbit is oval shaped, Mars is much further from the Sun than the Earth. This is labelled Conjunction: Mars is distant and faint.
The mixture of gases that surround a planet or a moon is called its . Earth’s atmosphere, what we call , has 78% nitrogen and 20% oxygen. There are also small amounts of other gases, including carbon dioxide (0.04%).
People could not breathe the atmosphere on Mars. It is 96% carbon dioxide and only 0.145% oxygen. The Martian atmosphere is also “thin.” This means that it is 100 times less dense than Earth’s atmosphere.
Both Earth and Mars experience four seasons. Each season on Mars is longer than each on Earth because the Martian year is longer.
The on Mars is colder, drier and harsher than in any place on Earth. Earth’s average temperature is 14 °C, but the average temperature on Mars is a chilly -63 °C. Mars is colder than Earth because it is farther from the Sun. The atmosphere of Mars is also too thin to trap heat on its surface.
A vast ocean system of liquid water covers 71% of Earth’s surface. There is water on Mars too, but the cold temperatures and thin atmosphere mean that liquid water cannot exist for long. At least not on the surface of the planet.
There is evidence that salty water flows in some places on the Martian surface. But this only happens when the temperature is above -23 °C. Mars has solid water in its polar ice caps like Earth does. There is also ice just below the surface of the planet. A tiny amount of water vapour exists in Mars’s atmosphere, and there is water ice in its clouds.
Image - Text Version
A colour photograph of the surface of Mars, from space.
The curvature of the planet is shown at the top of the image, with black space behind. Mars is mostly light reddish brown. In the centre of the surface, a thick, swirling cloud curls into a spiral shape. The cloud is mainly white with grey streaks around the left edge of it. Much smaller clouds are scattered to the left of the grey streak.
Precipitation like rain or snow is often part of the weather on Earth. Sometimes it “snows” on Mars too, but in a surprising way. The only kind of snow that makes it to Mars's surface is made of frozen carbon dioxide (CO2). This comes from carbon dioxide ice clouds.
Snow made from frozen water can fall from water ice clouds on Mars, but it does not reach the surface of Mars. It turns to water vapour in the thin atmosphere before it can land.
Just like on Earth, wind is a big part of the weather on Mars. Because the surface of Mars is so dry, dust storms are common. Strong winds, caused by uneven heating of the atmosphere, pick up dust from the planet’s surface and cause dust storms.
Sometimes dust storms cover the whole planet. They can even shape the surface of the planet! The biggest storms usually start during the summer in Mars’s southern hemisphere. Smaller dust devil storms are caused by swirling winds in a small area, just like on Earth.
By the Numbers
|Diameter1||12,756 km||6,792 km|
|Circumference2||40,075 km||21,339 km|
|Surface area||5.10 × 108 km2
|1.44 × 108 km2
|Volume||1.08 × 1012 km3
|1.63 × 1011 km3
|Mass||5.97 × 1024 kg||6.42 × 1023 kg|
|Average Density||5 514 kg/m3||3,933 kg/m3|
|Surface Gravity3||9.81 m/s2||3.71 m/s2|
|Minimum Temperature||-88 °C||-140 °C|
|Maximum Temperature4||58 °C||30 °C|
|Closest Distance to Sun
|1.47 × 108 km
|2.07 × 108 km
|Farthest Distance from Sun
|1.52 × 108 km
|2.49 × 108 km
(total length of orbit)
|9.40 × 108 km
|1.43 × 109 km
|Average Orbital Velocity||107,218 km/h||86,677 km/h|
|Day Length||24 hours||24 hours, 37 minutes|
|Year Length||365.25 days||687 Earth days|
|Number of Moons||1||2 (called Deimos and Phobos)|
|Planetary Magnetic Field8||Yes||No|
|Closest Distance to Earth||N/A||55.6 × 106 km|
|Farthest Distance from Earth||N/A||401 × 106 km|
|Table adapted from Mars Facts | All About Mars – NASA's Mars Exploration Program|
Rounded to the nearest whole number
Measured as gravitational acceleration at the planet's surface
Maximum temperature on Mars is during the summer at the equator when the Sun is shining on the surface.
Earth's orbit is nearly circular so perihelion and aphelion are similar; Mars' orbit is more elliptical.
Tilted axis of rotation causes seasons on Earth and Mars.
No magnetic field on Mars (plus thin atmosphere) means no protection from solar radiation.