Mars
Mars is the fourth planet from the Sun — a cold desert world of iron-oxide dust, polar ice caps and the largest volcano and canyon in the Solar System. Evidence shows it once had flowing water.
Key facts
Science
Physical
- Mass
- 6.42 × 10²³ kg · 0.107 M⊕
- Radius
- 3,390 km · 53% of Earth's radius
- Density
- 3,934 kg/m³ · 3.9× water
- Surface gravity
- 3.73 m/s² · 38% of Earth's
- Escape velocity
- 5.03 km/s · 45% of Earth's
- Axial tilt
- 25.19 °
Orbital
- Distance from the Sun
- 1.5 AU
- Semi-major axis
- 1.52 AU
- Eccentricity
- 0.09342
- Inclination
- 24.68 °
- Orbital period
- 1.88 years
- Perihelion
- 1.38 AU
- Aphelion
- 1.67 AU
- Mean orbital velocity
- 24.1 km/s
Rotation
- Rotation period
- 24.62 hours
Atmosphere
- Composition
- 95% CO₂, 2.6% N₂, 1.9% Ar
- Surface pressure
- 0.61 kPa
- Scale height
- 11.1 km
Temperature
- Minimum
- 130 K (-143 °C)
- Mean
- 210 K (-63 °C)
- Maximum
- 308 K (35 °C)
Composition
- Bulk composition
- Iron core, basaltic mantle; iron-oxide ('rust') surface dust
Radiation & temperature
- Insolation
- 0.431 S⊕ · 43% of the sunlight Earth receives
- Bond albedo
- 0.25 · reflects 25% of incoming sunlight
- Equilibrium temperature
- 210 K (-63 °C)
- Measured mean temperature
- 210 K (-63 °C)
Discovery & history
- First known
- Known since antiquity
- Name
- The Roman god of war, for its ominous blood-red colour.
Mars's reddish hue made it a symbol of war and blood across ancient cultures. Tycho Brahe's precise naked-eye measurements of its motion let Johannes Kepler deduce, in 1609, that planets orbit in ellipses — a cornerstone of modern astronomy. The telescope age brought (mistaken) 'canals' and dreams of life; the spacecraft age, beginning with Mariner 4 in 1965, revealed a cold desert that once had rivers and lakes.
- 1965Mariner 4Flyby
First successful Mars flyby; 21 photos showed a cratered, Moon-like surface.
- 1971Mariner 9Orbiter
First spacecraft to orbit another planet; mapped ~85% of Mars after a global dust storm cleared.
- 1971Mars 3Lander
First soft landing on Mars; transmitted for about 14.5 seconds before falling silent.
- 1976Viking 1Lander
First successful Mars lander; searched for life and imaged the surface for years.
- 1976Viking 2Lander
Second Viking lander, in Utopia Planitia; ran the biology experiments and watched frost form.
- 1997Mars Pathfinder / SojournerRover
Delivered the first Mars rover and demonstrated airbag landing.
- 20012001 Mars OdysseyOrbiter
Longest-running Mars orbiter; detected buried water ice and relays the surface rovers' data.
- 2004SpiritRover
Found mineral evidence of past water in Gusev crater; lasted six years, far beyond its 90-day plan.
- 2004OpportunityRover
Confirmed ancient liquid water at Meridiani Planum and roamed for over 14 years.
- 2008PhoenixLander
Landed in the Martian arctic and was first to touch and confirm water ice in the soil.
- 2012CuriosityRover
Confirmed Gale crater once held a habitable, long-lived lake.
- 2018InSightLander
Measured the deep interior of Mars, recording the first marsquakes with its seismometer.
- 2021PerseveranceRover
Caching rock samples for future return; flew the Ingenuity helicopter, the first powered flight on another world.
Images
Images from open archives · credit shown per image