The Red Planet
Mars
Mars is the fourth planet from the Sun: a cold, dusty desert world about half the size of Earth. Its rusty colour comes from iron oxide in its dust and rocks, earning it the name the Red Planet.
Today Mars has a thin atmosphere and no liquid water on its surface, but dried-up river valleys, ancient lake beds and minerals that form in water show it was once wetter. That history makes Mars one of the most important places to search for signs of past life, and the most explored planet beyond Earth.
Key facts
- Diameter
- 6,792 km0.53× Earth
- Mass
- 6.42 × 10²³ kg0.11× Earth
- Gravity
- 3.7 m/s²0.38 g
- Mean distance from Sun
- 1.52 AU≈ 228 million km
- Length of year
- 687.0 dEarth days or years
- Length of day
- 24.7 hSunrise to sunrise
- Mean temperature
- -65°CAt the surface
- Known moons
- 2+As of 2025
- Axial tilt
- 25.2°
1 astronomical unit (AU) is Earth's average distance from the Sun, about 149.6 million km. Values follow the NASA Planetary Fact Sheet; many are averages and vary with how and where they are measured.
Physical characteristics
Mars is 6,792 km across — a little over half Earth's diameter — and has about 11% of Earth's mass. Surface gravity is 3.7 m/s², or 38% of Earth's, so a 70 kg astronaut would feel as if they weighed about 26 kg.
Although small, Mars has roughly the same total surface area as all of Earth's dry land, because it has no oceans.
Atmosphere and climate
The atmosphere is about 95% carbon dioxide, with nitrogen and argon making up most of the rest. It is extremely thin: average surface pressure is less than 1% of Earth's, far too low for liquid water to last on the surface.
Mars is cold, with an average temperature around −65°C. On a summer day near the equator it can reach about 20°C, while winter nights at the poles fall below −120°C. Dust storms are common, and every few years one grows to engulf the entire planet for weeks — a 2018 global storm ended NASA's Opportunity rover mission.
Composition: CO₂ 95% · N₂ 2.8% · Ar 2%
Surface and interior
Olympus Mons
Mars hosts the largest volcano in the Solar System. Olympus Mons rises about 22 km above the surrounding plains — around two and a half times the height of Mount Everest above sea level — and is wider than many countries.
Valles Marineris
This vast canyon system stretches about 4,000 km and reaches depths of around 7 km. On Earth it would span the continental United States.
Polar ice and ancient water
Both poles have ice caps of water ice, topped in winter by a layer of frozen carbon dioxide. Orbiters and rovers have found river deltas, lake sediments and clay minerals that formed in water billions of years ago — Perseverance is exploring one such delta in Jezero Crater.
Inside Mars
Seismometer readings of 'marsquakes' by NASA's InSight lander showed that Mars has a crust, mantle and a large, liquid iron-rich core. Mars has no global magnetic field today, but magnetised rocks show it had one in the distant past.
Moons and rings
Mars has two small, irregularly shaped moons, Phobos (about 22 km across) and Deimos (about 12 km), discovered by Asaph Hall in 1877. Whether they are captured asteroids or debris from an ancient impact is still debated.
Phobos orbits so close that it is slowly spiralling inward; in roughly 50 million years it is expected to crash into Mars or break apart into a ring. Mars has no rings today.
Orbit and rotation
Mars orbits at an average of 1.52 AU (about 228 million km) and takes 687 Earth days to complete a year. Its orbit is noticeably elliptical, which makes its seasons uneven in length.
A Martian day, called a sol, lasts 24 hours 39 minutes — very close to Earth's. Its axial tilt of about 25° gives Mars seasons much like Earth's, each roughly twice as long. Earth and Mars line up favourably every 26 months, which is why Mars missions launch in batches.
Exploration and missions
More spacecraft have been sent to Mars than to any other planet, and several are working there today.
- 1965
Mariner 4 · NASA
Returned the first close-up images of another planet during a flyby.
- 1971
Mariner 9 · NASA
Became the first spacecraft to orbit another planet and mapped Olympus Mons and Valles Marineris.
- 1976
Viking 1 & 2 · NASA
Two orbiters and landers that returned the first long-term surface data and colour images.
- 1997
Mars Pathfinder & Sojourner · NASA
Delivered the first rover to operate on Mars.
- 2004–2018
Spirit & Opportunity · NASA
Twin rovers that found strong evidence of past water; Opportunity drove more than 45 km.
- 2012–
Curiosity · NASA
A car-sized rover exploring Gale Crater and Mount Sharp's layered rocks.
- 2021–
Perseverance & Ingenuity · NASA
Perseverance is collecting rock samples in Jezero Crater; Ingenuity made the first powered, controlled flight on another planet.
- 2021–
Tianwen-1 & Zhurong · CNSA
China's first Mars mission, combining an orbiter, lander and rover.
Surprising facts about Mars
- Sunsets on Mars look blue, because fine dust scatters blue light forward near the Sun.
- Mars has the tallest volcano in the Solar System.
- Its moon Phobos is slowly falling towards the planet.
- Mars has roughly the same surface area as Earth's dry land.
- In 2021 a small helicopter, Ingenuity, flew in Mars's thin air — something many thought impossible.
Mars compared with Earth
| Property | Mars | Earth |
|---|---|---|
| Diameter | 6,792 km | 12,756 km |
| Mass (Earth = 1) | 0.108 | 1.000 |
| Gravity | 0.38 g | 1.00 g |
| Day | 24.7 h | 24.0 h |
| Year | 687.0 d | 365.2 d |
| Mean temperature | -65°C | 15°C |
| Moons | 2 | 1 |
Keep exploring
- Earth: the ocean world that supports life
- Jupiter: king of the planets
- Venus: earth's scorching twin
- Europa Clipper — searching for a habitable ocean
- Hera — a crash-scene investigator for planetary defence
- Psyche — journey to a metal world
- Fly to Mars in the interactive 3D solar system
- All eight planets of the Solar System