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# Earth vs. Mars

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Let's Talk Science
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Learn about the characteristics of the Earth and Mars, two planets in our Solar System.

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.

## Planetary Basics

Mars is smaller than earth. The equatorial diameter of Mars is about half that of the Earth. The circumference 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 Earth open and empty like an eggshell, about 6.5 Mars planets would fit inside.

Mars is not just smaller than Earth, it is also less dense. Though Mars is 15% of Earth’s volume, it is only 11% of Earth’s mass. This means that the pull of gravity on the surface of Mars is only 38% as strong as the pull of gravity on Earth’s surface.

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 weight 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.

Did you know?

You can calculate your weight on another planet. Check out the “What is your weight on another planet?” activity.

## Two Rocky Planets

Earth and Mars are both rocky planets. They both have similar kinds of iron-rich rocks at 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.

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 active now.

## 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 is like that spinning top drawing a 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!

## Atmosphere

The mixture of gases that surround a planet or a moon is called its atmosphere. Earth’s atmosphere, what we call air, has 78% nitrogen and 20% oxygen. There are also small amounts of other gases, including carbon dioxide (0.04%).

The atmosphere on Mars would be suffocating for humans. It is 96% carbon dioxide and only 0.145% oxygen. The Martian atmosphere is also “thin.” It is 100 times less dense than Earth’s atmosphere.

## Climate

Both Earth and Mars experience four seasons, but each season is longer on Mars because the Martian year is longer.

The climate on Mars is colder, drier and harsher than 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 retain 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 briny (salty) liquid 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.

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. 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 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 they cover the whole planet and it even shapes 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

Earth vs. Mars
Property Earth Mars
Diameter1 12,756 km 6,792 km
Circumference2 40,075 km 21,339 km
Surface area 5.10 × 108 km2
(510,064,472 km2)
1.44 × 108 km2
(144,371,391 km2)
Volume 1.08 × 1012 km3
(1,083,206,916,846 km3)
1.63 × 1011 km3
(163,115,609,799 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
(called perihelion)5
1.47 × 108 km
(147,098,291 km)
2.07 × 108 km
(206,655,215 km)
Farthest Distance from Sun
(called aphelion)6
1.52 × 108 km
(152,098,233 km)
2.49 × 108 km
(249,232,432 km)
Orbital Distance
(total length of orbit)
9.40 × 108 km
(939,887,974 km)
1.43 × 109 km
(1,429,085,052 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
Axial Tilt7 23.5° 25.2°
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
Glossary

Air
The common name of Earth’s atmosphere.

Atmosphere
The layer of gases that surround some planets and moons. The gasses are held in place by gravity.

Axis
An imaginary line around which an object (such as a planet) rotates

Climate
The normal weather pattern over a long period of time, in a large geographical area. Climate can change over hundreds or thousands of years. It does not change day-to-day like weather.

Day
The length of time it takes a planet to complete one full rotation around its axis.

Density
A measure of how much mass, or matter is in a given volume. Objects with higher density have more matter than objects with lower density, even if they have the same volume. A metal ball is more dense than a cotton ball, for example.

Equatorial circumference
The distance around a planet. This is measured on its surface following the line of the equator.

Equatorial diameter
The distance through the middle of a planet. This is measured from opposite points on the equator.

Gravity
The attractive or pulling force between any objects that have mass. For example, Earth’s gravity keeps people and objects on the surface of the planet. The Sun’s gravity keeps all the planets in orbit.

Mass
A measure of the amount of matter in an object.

Sol
The name for one day on Mars.

Weather
The mix of events in the atmosphere, in a particular area. This can be things like clouds, precipitation or wind. Weather can change from hour to hour. It also changes over short distances. Between nearby cities in the same province for example.

Weight
A measurement of the force of gravity on an object. An object’s mass, or the amount of matter it has, is fixed. But its weight depends on the force of gravity where it is.

Year
The length of time for a planet to complete one full revolution around the Sun, following its orbital path.

Mars Facts
A collection of animations and infographics from NASA's Mars Exploration Program about the Red Planet.

Curiosity Rover Report (May 11, 2016): Mars Weather Report (2016)
Video (2:32 min.) from NASA's Jet Propulsion Laboratory about what the rover learned about the weather on Mars during its mission.

Mars Weather
Website from NASA to see today’s weather report on Mars!

How Long Would You Survive on Mars? (2015)
With this video (3:06 min.) from SciShow Space, find out what it would be like to stand on the surface of Mars without a spacesuit.

Opportunity: NASA Rover Completes Mars Mission (2019)
Video (3:51 min.) from NASA looks at the journey the Opportunity rover took across the surface of Mars, and the photos it took along the way.

Generation Mars (Part 1 and Part 2) (2016)
CBC Ideas podcast (53:59 min. and 54:00 min.) with a group of authors, astronauts, and Mars scholars discussing the challenges of getting humans to Mars and living there.

Why do we have seasons? (2019)