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. What Curiosity and Perseverance found at Gale crater and Jezero is organic carbon of unresolved origin, not evidence of life: lifeless chemistry makes the same molecules as readily as biology does.
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
- Computed from mass and radius
- Surface gravity
- 3.73 m/s² · 38% of Earth's gravity
- Computed from mass and radius
- Escape velocity
- 5.03 km/s · 45% of Earth's escape velocity
- Computed from mass and radius
- Axial tilt
- 25.19 °
Orbital
- Distance from the Sun
- 1.58 AU
- Computed from the position at the selected time
- Semi-major axis
- 1.52 AU
- Computed from the cached state vector
- Eccentricity
- 0.09341
- Computed from the cached state vector
- Inclination
- 24.68 °
- Computed from the cached state vector
- Orbital period
- 1.88 years
- Computed from the cached state vector
- Perihelion
- 1.38 AU
- Computed from the orbital elements
- Aphelion
- 1.67 AU
- Computed from the orbital elements
- Mean orbital velocity
- 24.1 km/s
- Computed from the orbital elements
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
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
- Bond albedo
- 0.25 · reflects 25% of incoming sunlight
- Equilibrium temperature
- 210 K (-63 °C)
- Computed from albedo + distance from the Sun (airless black body)
- 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.
The first spacecraft to fly past Mars — silent since March; the distance is given as 193,000 or 197,000 km.
First successful Mars flyby; 21 photos showed a cratered, Moon-like surface.
Silent by then; the sources put its distance from Mars at 1,500 km (NSSDCA) or 650,000 km (Beyond Earth).
First of the twin 1969 Mars flybys; returned ~75 images and showed the air is ~98% CO₂ and the south polar cap is frozen CO₂.
Returned 126 images — the most yet — including a full-disc view of the bright spot later recognised as the volcano Olympus Mons.
First spacecraft to orbit another planet; mapped ~85% of Mars after a global dust storm cleared.
Its lander crashed, the first human-made object to reach the surface of Mars; its orbiter worked until 1972.
First soft landing on Mars; transmitted for about 14.5 seconds before falling silent.
Unable to enter orbit, it flew past, took 12 pictures and made the first detection of the night-side ionosphere.
Worked in orbit for about two weeks and photographed signs of erosion by flowing water south of Valles Marineris.
Sent the first data from inside the atmosphere of Mars as it descended; contact was lost as it reached the surface.
First successful Mars lander; searched for life and imaged the surface for years.
Second Viking lander, in Utopia Planitia; ran the biology experiments and watched frost form.
Studied Mars from orbit for two months before contact was lost.
Delivered the first Mars rover and demonstrated airbag landing.
Mapped Mars for seven years: its shape, the magnetism of its ancient crust, and hematite where Opportunity later landed.
Lost during its landing near the south pole; the probable cause was a software flaw that shut its engines off too early.
Two probes built to strike the ground near the south pole; neither was heard from.
Longest-running Mars orbiter; detected buried water ice and relays the surface rovers' data.
Japan's first Mars mission passed about 1,000 km above the surface after its attempt to enter orbit was given up.
Found mineral evidence of past water in Gusev crater; lasted six years, far beyond its 90-day plan.
Confirmed ancient liquid water at Meridiani Planum and roamed for over 14 years.
Landed in the Martian arctic and was first to touch and confirm water ice in the soil.
Confirmed Gale crater once held a habitable, long-lived lake.
Measured the deep interior of Mars, recording the first marsquakes with its seismometer.
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