Mars vs Earth

Mars compared to Earth, side by side

Mars is smaller, lighter and colder than Earth, and farther from the Sun. Here are the two planets side by side, from NASA’s fact sheets.[1][2]

Values from NASA’s Mars and Earth fact sheets, except the temperatures (NASA), the length of a sol (NASA GISS) and the magnetic fields (NASA). Surface areas (from the fact sheets’ mean radii), miles and the last column are our calculation.[1][2][3][4][5][6]

How big is Mars compared to Earth?

Mars is about half as wide as Earth: 6,779 km (4,212 mi) across on average, against Earth’s 12,742 km (7,918 mi).[1][2] NASA puts it this way: if Earth were the size of a nickel, Mars would be about as big as a raspberry.[3]

Half as wide means much smaller overall. Mars has about 28% of Earth’s surface area, 15% of its volume and 11% of its mass.[1][2] It is also less dense, at 3,934 kg per cubic meter against Earth’s 5,513.[1]

So Earth is the bigger planet, by a long way: its volume is about 6.6 times Mars’s.[1] But Mars has a lot of ground. Its whole surface, about 144 million km² (56 million mi²) by our calculation, is nearly the same area as Earth’s dry land, NASA says.[1][3] On Earth, the ocean covers about 71% of the surface.[4]

How strong is Mars’s gravity compared to Earth’s?

Gravity on Mars is 38% of Earth’s: 3.73 m/s² against 9.82 m/s².[1] Someone who weighs 70 kg (154 lb) on Earth would weigh about 27 kg (59 lb) on Mars. Leaving is easier too: a spacecraft needs 5.0 km/s to escape Mars’s pull, against 11.2 km/s for Earth.[1] Try your own weight in the Mars gravity calculator.

How long are a day and a year on Mars?

A day on Mars lasts 24 h 39 min 35 s, about 40 minutes longer than Earth’s. A year lasts 687 Earth days.[3][6] Scientists call a Mars day a solSolA sol is a day on Mars — 24 h 39 min 35 s, about 40 minutes longer than ours — and rovers count them from the day they land.More in the glossary. A Mars year is 1.88 Earth years, so each season lasts much longer than ours.[1][3]

Mars’s axis is tilted 25.2°, close to Earth’s 23.4°, so like Earth it has seasons.[1][3] Its stretched orbit makes those seasons uneven, from about 142 to 194 sols.[3] More on Mars days, years and seasons, and on how its distance from the Sun changes through the year.

How do the temperature and air compare?

Mars is much colder: NASA puts its median surface temperature at about −65 °C (−85 °F), against an average of 15 °C (59 °F) on Earth.[5] At its average distance, Mars gets 43% of the sunlight Earth does, and its thin air lets heat from the Sun escape easily.[1][3] Temperatures range from about 20 °C (68 °F) at the warmest to about −153 °C (−243 °F) at the coldest.[3]

The air is very different. On Mars it is 95% carbon dioxide, and the pressure at the surface is about 0.6% of Earth’s. Earth’s air is 78% nitrogen and 21% oxygen.[1][2] More on Mars weather and the atmosphere of Mars.

Does Mars have water and a magnetic field like Earth?

Not like Earth’s. The ocean covers about 71% of Earth.[4] On Mars the air is too thin for liquid water to last long on the surface. Water on Mars today includes ice just under the surface in the polar regions, NASA says.[3] More on water on Mars.

Earth’s fast spin and molten nickel-iron core give it a global magnetic field.[4] Mars has no global magnetic field today. Parts of its southern crust are strongly magnetized, though: traces of a field from about 4 billion years ago.[3]

Was Mars once like Earth?

In some ways, yes. Scientists think that billions of years ago Mars’s air was much denser, NASA says, and the planet was warm enough for rivers, lakes and perhaps even oceans. As Mars cooled and lost its global magnetic field, the solar wind and solar storms stripped much of its air away to space, leaving the cold, dry desert we see today.[7] NASA’s MAVEN orbiter found that most of the gas ever present in Mars’s atmosphere has been lost to space.[8]

The European Space Agency points to size. Mars is smaller than Earth but of a similar age, so its outer layers have cooled and hardened to a greater depth than Earth’s. Its global magnetic field lasted only for its first few hundred million years, ESA says.[9] NASA’s InSight lander found that Mars’s core is still at least partly molten, but the global field is gone.[10] A 2025 study of InSight’s quake data, published in Nature, reported a solid inner core about 600 km (370 mi) in radius at the center.[11] Earth’s core still makes one today.[4]

Sources

1. NASA NSSDCA — Mars Fact SheetPrimary · checked Oct 6, 2026
2. NASA NSSDCA — Earth Fact SheetPrimary · checked Oct 6, 2026
3. NASA Science — Mars: FactsPrimary · checked Oct 6, 2026
4. NASA Science — Facts About EarthPrimary · checked Oct 6, 2026
5. NASA Science — Temperatures Across Our Solar SystemPrimary · checked Oct 6, 2026
6. NASA GISS — Mars24 Sunclock — Technical Notes on Mars Solar TimePrimary · checked Oct 6, 2026
7. NASA Science — NASA: New Insights into How Mars Became UninhabitablePrimary · checked Oct 6, 2026
8. NASA — NASA’s MAVEN Reveals Most of Mars’ Atmosphere Was Lost to SpacePrimary · checked Oct 6, 2026
9. ESA — Martian Interior (Mars Express)Primary · checked Oct 6, 2026
10. NASA Science — InSight: Science HighlightsPrimary · checked Oct 6, 2026
11. Nature (Bi et al., Sep 3, 2025) — Seismic detection of a 600-km solid inner core in MarsPrimary · checked Oct 6, 2026