Mars
Mars is the fourth planet from the Sun, orbiting between Earth and Jupiter. It is a cold rocky world with a thin atmosphere, polar caps and two small moons. Its surface preserves the traces of ancient rivers and lakes alongside enormous volcanoes and canyons extending for thousands of kilometres.[2]
Size and physical characteristics
Mars has a mean diameter of about 6,779 km, slightly more than half that of Earth. Its total surface area, approximately 144 million km², is nearly equal to the land area of Earth. Mars has no modern oceans concealing a large share of its terrain beneath water.[2]
The planet has a mass of 6.42 × 1023 kg, roughly one ninth of Earth's, and an average density of about 3.93 g/cm³. Surface gravity is almost three times weaker than on Earth: an object pressing on a terrestrial surface with a force of 100 newtons would exert about 38 newtons on Mars.[3]
Mars is also slightly flattened at the poles. Its equatorial and polar radii differ by about 20 km.[1]
Orbit, rotation and seasons
A Martian year lasts approximately 687 Earth days. Mars travels around the Sun at an average speed of about 24 km/s, covering nearly 1,450 kilometres each minute. Its distance from the Sun ranges from about 207 million km at perihelion to 249 million km at aphelion.[1]
A solar day on Mars is called a sol. It lasts about 24 hours 39 minutes, only 39 minutes longer than an Earth day. The rotation axis is tilted by about 25°, giving Mars a sequence of spring, summer, autumn and winter. Each season is longer on average than its terrestrial counterpart, and the planet's eccentric orbit produces considerable differences in their duration.[4]
Colour and surface composition
Oxidised iron compounds in the dust and surface material give Mars its reddish colour. Fine dust covers vast regions and is frequently lifted into the atmosphere. At close range, the Martian landscape is much more varied than the nearly uniform red disc visible from Earth: images reveal grey rocks, dark sands and pale sedimentary layers.[5]
The colour of Martian dust can be reproduced by a mixture of basaltic material and ferrihydrite, a hydrated iron(III) mineral. Its presence may connect the formation of the dust with ancient conditions in which liquid water existed on Mars.[5]
Volcanoes and canyons
Mars is home to Olympus Mons, the largest known volcano in the Solar System. Its base spans roughly 600 km, while its summit rises about 22 km above the Martian reference level. By this measure it is approximately two and a half times the height of Mount Everest. The slopes are exceptionally gentle because the immense shield volcano grew through repeated lava flows.[6]
Another giant landform is Valles Marineris, a canyon system about 4,000 km long. Individual troughs reach depths of approximately 7 km. In length, the system is almost ten times greater than the Grand Canyon in the United States.[7]
Broad lowlands dominate the northern hemisphere, whereas the southern terrain is generally higher and much more densely covered by ancient impact craters. This contrast is prominent on global topographic maps.[8]
Internal structure and seismic activity
Mars consists of a rocky crust, mantle and metallic core. The InSight lander recorded more than a thousand marsquakes and used their seismic waves to investigate these layers. One of the strongest detected events occurred in May 2022 and had a magnitude of about 5.[9]
An analysis of InSight data published in 2025 found evidence for a solid inner core with a radius of about 600 km, surrounded by a liquid metallic region. The result refines models of how the Martian interior formed and cooled.[10]
Atmosphere and dust storms
The atmosphere consists primarily of carbon dioxide. Mean surface pressure is only about 0.6% of Earth's, with higher pressure in low-lying regions and lower pressure at high elevations. This thin envelope retains little heat, producing large temperature changes over the course of a day.[1][2]
Winds transport dust and sand, build dunes and generate dust devils. Some storms expand until they encircle the planet. During the global storm of 2018, airborne dust reduced sunlight so severely that the solar-powered Opportunity rover could no longer generate enough energy. Its final signal was received on 10 June 2018.[11]
Water and polar regions
Water on present-day Mars survives mainly as ice. Deposits occur in the polar regions and beneath the surface, including at middle latitudes. Orbital instruments map this ice, while recent impact craters sometimes expose bright water ice immediately beneath the soil.[12][9]
The polar caps change with the seasons. During colder periods, some atmospheric carbon dioxide freezes into a layer of dry ice; as temperatures rise, it returns to the atmosphere. Seasonal changes therefore alter not only the appearance of the poles but also the mass of the atmosphere.[4]
Ancient Mars held much more water on its surface. Jezero crater preserves deposits formed by a lake and river delta, where flowing water delivered sand, silt and minerals that accumulated in layers. The Perseverance rover studies these rocks to reconstruct the history of the former lake.[13]
Magnetic field and atmospheric loss
Modern Mars has no strong global magnetic field comparable to Earth's. Some regions of the crust retain magnetisation left by an ancient field. The solar wind interacts directly with the upper atmosphere and carries some of its material into space.[14][2]
The MAVEN mission studied atmospheric escape from Martian orbit. Its measurements showed how charged particles and solar radiation contribute to erosion of the atmosphere. In 2025, researchers reported the first direct observation at Mars of sputtering, a process in which energetic particles knock atoms out of the upper atmosphere.[14] NASA declared the mission complete on 3 June 2026 after contact had been lost on 6 December 2025.[15]
Moons
Mars has two small moons, Phobos and Deimos. Both are irregularly shaped and heavily cratered. Phobos is larger and orbits closer to the planet, completing one revolution in about 7 hours 39 minutes. Deimos takes approximately 30 hours 18 minutes. Both moons keep the same side facing Mars.[16]
Phobos is gradually moving closer to Mars. In the distant future, tidal forces may break it apart into a ring of debris, or the moon may collide with the planet.[17]
Exploration and the search for life
Mariner 4 returned the first close-range images of Mars in 1965. In 1971, the Soviet Mars 3 spacecraft made a soft landing, although communication from the surface soon ceased. In 1976, the Viking 1 and Viking 2 landers began long-term investigations of the soil and atmosphere.[18][19][20]
The Curiosity and Perseverance rovers investigate rocks formed in ancient watery environments. Martian samples contain organic compounds, but such molecules can arise through non-biological processes; their presence alone does not demonstrate that life existed on Mars.[21]
In 2025, NASA reported potential biosignatures in a sample collected by Perseverance from rocks of the Bright Angel formation. The combination of minerals, organic matter and rock textures permits a biological explanation but also requires further testing. The finding has not been accepted as confirmation of Martian life.[22]
See also
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 Mars Fact Sheet // NASA, National Space Science Data Center.
- ↑ 2.0 2.1 2.2 2.3 2.4 Mars: Facts // NASA Science.
- ↑ Planetary Fact Sheet — Metric // NASA, National Space Science Data Center.
- ↑ 4.0 4.1 Helio and You: Seasons on Earth, Mars, and Beyond // NASA Science.
- ↑ 5.0 5.1 Have we been wrong about why Mars is red? // European Space Agency. 25 February 2025.
- ↑ Olympus Mons on Mars // European Space Agency.
- ↑ Mars Express peers into Mars' ‘Grand Canyon’ // European Space Agency. 20 July 2022.
- ↑ Geography of Mars // European Space Agency.
- ↑ 9.0 9.1 InSight: Science Highlights // NASA Science.
- ↑ Seismic detection of a 600-km solid inner core in Mars // Nature. 2025.
- ↑ Mars Dust Storm — 2018 // NASA Mars Exploration Program.
- ↑ SWIM Map Shows Subsurface Water Ice on Mars // NASA Science. 26 October 2023.
- ↑ Perseverance Science Highlights // NASA Science.
- ↑ 14.0 14.1 NASA’s MAVEN Makes First Observation of Atmospheric Sputtering at Mars // NASA Science. 29 May 2025.
- ↑ MAVEN // NASA Science.
- ↑ Mars Moons: Facts // NASA Science.
- ↑ Phobos // NASA Science.
- ↑ Mariner 4 // NASA Science.
- ↑ 19 May: Mars 2 and Mars 3 // European Space Agency.
- ↑ Viking Project // NASA Science.
- ↑ NASA’s Curiosity Finds Organic Molecules Never Seen Before on Mars // NASA Jet Propulsion Laboratory. 21 April 2026.
- ↑ NASA Says Mars Rover Discovered Potential Biosignature Last Year // NASA. 10 September 2025.