Mars is a cold desert world with the largest volcano and the deepest canyon in the Solar System. Dry riverbeds and minerals that only form in water tell us it was once warmer and wetter - which is why it is the prime target in the search for past life.
Olympus Mons is ~22 km tall - two and a half times Mount Everest.
A Mars day (sol) is 24 h 40 m - just slightly longer than ours.
Its red colour is iron oxide: the planet is literally rusty.
A world that lost its air
Mars is small, so its gravity is weak and its interior cooled early, shutting down its magnetic field. Without that shield, the solar wind stripped most of its atmosphere away - and with it went the pressure needed for liquid water.
Physical characteristics
Diameter
6,792 km
Mass
6.420e+23 kg
Surface gravity
3.7 m/s²
Density
3.93 g/cm³
Rotation period
24.62 h
Axial tilt
25.2°
Mean temperature
-65 °C
Temperature range
-153 °C to 20 °C
Geometric albedo
0.17
Known moons
2
Atmosphere and composition
Atmosphere
95% CO₂ with nitrogen and argon at ~0.006 bar - so thin that liquid water is unstable: exposed water either freezes or boils away, even in the cold.
Composition
An iron-sulfur core and silicate mantle beneath a basaltic crust dusted with rust-red iron oxide.
Interior structure
Liquid coreobserved
Molten iron-nickel-sulfur, larger and lighter than models expected.
Mantleobserved
A single rocky shell; its dying convection once fed the giant volcanoes.
Crustobserved
24-72 km thick, thicker in the southern highlands.
How we know: NASA’s InSight lander listened to marsquakes from 2018-2022; the waves passing through the planet measured the core, mantle and crust directly.
Viking 1 achieved the first fully successful landing on Mars on 20 July 1976 and sent back the first photographs ever taken from the Martian surface. Its lander kept working until November 1982.
Mars ExpressESA · Orbiter · 2003 · active
ESA’s first mission to another planet has been orbiting Mars since December 2003. Its cameras and radar have mapped buried water ice, ancient water-carved terrain, and made the closest-ever flybys of Phobos.
Curiosity (Mars Science Laboratory)NASA · Rover · 2011 · active
The car-sized Curiosity rover was lowered into Gale Crater by a rocket-powered “sky crane” in August 2012. It proved the crater once held a long-lived freshwater lake - an environment that could have supported microbial life - and is still climbing Mount Sharp today.
PerseveranceNASA · Rover · 2020 · active
Perseverance landed in Jezero Crater in February 2021 to explore an ancient river delta and cache rock samples for a future return to Earth. It carried the Ingenuity helicopter, which made the first powered flight on another planet and went on to fly 72 times.
James Webb Space TelescopeNASA/ESA/CSA · Space telescope · 2021 · active
The most powerful space telescope ever built, JWST observes the infrared universe with a 6.5 m gold-coated mirror from a point 1.5 million km beyond Earth. Alongside the distant cosmos it studies Solar System targets, from Jupiter’s auroras to the surfaces of Kuiper belt worlds.