Mars

Mars is the fourth planet from the Sun, a cold desert world 6,779 km across, about half Earth's diameter, with a day 37 minutes longer than Earth's.^[1] Oxidized iron in fine, windblown dust gives the planet its color. Billions of years ago Mars had rivers and lakes, and possibly seas; today its water survives mainly as polar ice and buried ice, with traces of vapor in a thin carbon dioxide atmosphere.

As of August 2026, six orbiters and two NASA rovers are operating at Mars.^[2][3][4] The fleet shrank when NASA's MAVEN orbiter fell silent in late 2025. The existing Mars Sample Return campaign has been terminated, leaving Perseverance's sealed rock cores on the surface with no approved retrieval mission.^[5][6] Crewed missions remain a long-term goal, but none has an approved launch date.

Physical characteristics#

Mars has a diameter of 6,779 km and a surface gravity of 3.71 m/s², about 38 percent of Earth's. It orbits the Sun at an average distance of 228 million km, about 1.5 times as far out as Earth.^[1] Its axis tilts 25 degrees, so it has seasons, each nearly twice as long as Earth's because the year lasts 687 days. The average surface temperature is about -63 °C, though summer afternoons near the equator can climb above freezing while polar winter nights drop below -120 °C. Both poles carry permanent water ice caps topped by seasonal layers of carbon dioxide frost. Mars lost its global magnetic field billions of years ago and now retains only patches of crustal magnetism.

Why is Mars red?#

Mars looks red because its fine dust is rich in oxidized, ferric iron. Winds spread the submicron grains over much of the darker basaltic surface, and their ferric minerals reflect a red-orange color. Calling this coating "rust" is useful shorthand, but the exact iron mineral has been debated. Rover measurements established that airborne dust is more oxidized than nearby rocks and soils.^[7]

A 2025 Nature Communications study compared orbital and surface spectra with laboratory mixtures and found that ferrihydrite mixed with basalt reproduced the dust spectrum better than the long-favored anhydrous mineral hematite. Ferrihydrite contains water in its structure, so the authors argue that much of the dust pigment formed in cold, oxidizing, wetter conditions early in Mars's history. The result does not directly date the dust or identify a single place where it formed.^[8]

Phobos and Deimos#

Asaph Hall discovered Mars's two moons, Phobos and Deimos, in August 1877. Phobos, the larger at about 22 km across, orbits only some 6,000 km above the surface and laps the planet three times in a Martian day. Deimos, roughly 12 km across, keeps a much wider orbit and takes about 30 hours to go round. Tides are dragging Phobos down by about 1.8 m per century, and NASA expects it to either strike Mars or break apart into a ring within roughly 50 million years.^[9] Whether the moons are captured asteroids or debris that reaccreted after a large impact remains unsettled. JAXA's Martian Moons eXploration mission is intended to help answer that question by returning material from Phobos.^[10]

Olympus Mons and Valles Marineris#

Mars holds some of the solar system's most extreme terrain. Olympus Mons, a shield volcano roughly 600 km wide, rises about 22 km above its surroundings, nearly two and a half times the height of Mount Everest. It could grow so large because Mars lacks moving tectonic plates, allowing repeated lava flows to build in one region. Olympus Mons stands at the edge of the Tharsis rise, which carries three more giant volcanoes. To the east, Valles Marineris stretches more than 4,000 km, about a fifth of the planet's circumference, and reaches depths near 7 km. The canyon system began mainly through crustal extension associated with Tharsis and was later widened by collapse, landslides, and some water erosion. The USGS global geologic map integrates topography, imaging, spectroscopy, and other remote-sensing evidence used to reconstruct this history.^[11]

Evidence for ancient water#

Orbital images show branching valleys, giant outflow channels, and river deltas. Spectrometers on the European Space Agency's Mars Express and NASA's Mars Reconnaissance Orbiter have mapped clays and sulfate salts produced through interactions with water. Surface missions added chemical and sedimentary evidence. Opportunity found hematite spherules and acid-water minerals. Curiosity showed that Gale crater's Yellowknife Bay once held a lake with near-neutral pH, low salinity, and chemical energy sources that could have supported microorganisms. This establishes ancient habitability, not that organisms were present.^[12] A 2025 carbonate study offered a more intermittent climate model, with local wet intervals followed by drying as carbon dioxide became locked in rock. That model does not show that early Mars was continuously warm or globally habitable.^[13]

Perseverance has been sampling Jezero crater's ancient river and lake deposits since 2021. In 2025, its team reported that the organic-bearing Cheyava Falls mudstone contains reaction fronts and nodules enriched in minerals interpreted as vivianite and greigite. Similar associations can be produced by microbes on Earth, but non-biological reactions can also make the minerals. The team therefore classifies the feature as a potential biosignature, not evidence of life.^[14] In June 2026, a separate analysis reported hundreds of detections of spatially distributed, complex organic matter in two Bright Angel mudstones. It was the strongest such detection reported at Jezero, but organic carbon can have biological or non-biological origins.^[15]

Evidence for a former northern ocean remains suggestive rather than conclusive. Zhurong's ground-penetrating radar imaged 76 buried layers 10 to 35 m down along 1.3 km of its route in Utopia Planitia. The layers dip north, and the authors interpreted them as coastal deposits built by waves and tides, while recognizing that the result depends on the geologic interpretation of radar profiles.^[16] In 2026, another team trained a classifier on simulated and laboratory spectra and applied it to millions of orbital spectra plus Zhurong data. The model inferred manganese (hydr)oxides concentrated in a narrow elevation band; a separate depositional model estimated that water persisted for 0.8 to 1.5 million years. Both the mineral identification and duration are model-based. They do not by themselves prove an ocean, a shoreline, or biology.^[17]

Water beneath the surface#

Mars did not lose all of its water. Both polar caps are largely water ice. Radar and thermal data from Mars Reconnaissance Orbiter, Mars Odyssey, and the retired Mars Global Surveyor have been combined into maps of buried ice from the polar regions into the mid-latitudes, identifying deposits that may be shallow enough for future robotic or crewed access.^[18]

Zhurong's radar added a site-specific clue in 2026. Researchers reported a low-loss layer about 15 m below Utopia Planitia, roughly 7 m thick, whose dielectric properties are consistent with an ice-regolith mixture. They interpret it as shallow "dirty ice," but no drill has sampled it and the identification remains an inference from radar.^[19]

How much water sits deeper is disputed. A 2024 analysis of seismic velocities recorded by NASA's InSight lander concluded that fractured igneous rock roughly 11.5 to 20 km down may be saturated with liquid water. If the landing site were globally representative, the inferred amount could cover Mars 1 to 2 km deep.^[20] The calculation depends on assumptions about pore shape and mineral composition. A 2025 comment argued that the same seismic and gravity data do not require a water-saturated mid-crust.^[21] Either way, such depths are beyond any drill sent to Mars.

Atmosphere and climate#

Mars's atmosphere is about 95 percent carbon dioxide at a surface pressure near 6 millibars, less than 1 percent of Earth's and too thin for liquid water to remain stable on most of the surface today.^[1] Dust storms occur every year and sometimes merge into planet-circling events; the 2018 global storm ended the solar-powered Opportunity rover's mission. Measurements by MAVEN showed how solar radiation and the solar wind remove gas from the upper atmosphere, helping explain the loss of an earlier, denser atmosphere. MAVEN also made the first direct observation of sputtering at Mars, in which particles accelerated by the solar wind knock atmospheric particles into space.^[22]

Methane remains unresolved. Curiosity has reported faint background methane and occasional spikes at the surface, while ESA's Trace Gas Orbiter has not detected methane from orbit. A 2025 reanalysis identified possible contamination and pressure effects inside Curiosity's Tunable Laser Spectrometer, but did not conclude that every detection was an artifact. Its authors proposed an experiment to separate a Martian signal from an instrumental one.^[23] Methane can be produced by biology, geology, or contamination, so even a confirmed detection would not establish life without its source being identified.

Could Mars support life?#

Ancient Mars could have supported microbial life in at least some lakes and groundwater systems: Curiosity found that Yellowknife Bay had liquid water, key chemical elements, usable energy gradients, and mild water chemistry.^[12] That means the environment was habitable. It does not mean it was inhabited. On present-day Mars, the exposed surface is cold, dry, irradiated by ultraviolet and cosmic radiation, and chemically oxidizing. A protected subsurface environment remains a scientific possibility, but no current habitat or Martian organism has been confirmed.^[24]

These terms answer different questions and should not be treated as synonyms:

In short, ancient Mars was habitable in places, modern subsurface habitability remains unresolved, and there is no confirmed evidence of past or present Martian life.

Exploration history#

Mars exploration advanced through a few decisive changes in capability, from brief flybys to orbiters, long-lived rovers, aerial flight, and sample caching.^[27]

Zhurong became the first rover other than a US spacecraft to operate on Mars. It drove about 1,921 m before entering winter dormancy in May 2022 and has not resumed reported operations. Ingenuity completed 72 flights before rotor damage ended its mission in January 2024. India's ISRO operated the Mars Orbiter Mission from 2014 to 2022.

How long does a trip to Mars take?#

Most robotic trips from Earth to Mars take about 6 to 9 months. NASA describes a typical cruise as roughly 200 days; Perseverance took about seven months.^[27][31] A spacecraft does not fly along the momentary straight-line distance. It follows an arc around the Sun timed to meet Mars, and favorable launch opportunities recur about every 26 months.

A minimum-energy crewed round trip would take much longer than the two cruise legs. NASA mission studies generally allocate 6 to 9 months each way and a 300 to 500 day stay near or on Mars while the planets move into position for the return. The complete mission is therefore about 3 to 3.5 years. Faster propulsion or a higher-energy trajectory could shorten transit, but at the cost of more energy, mass, or risk.^[31]

The fleet at Mars in 2026#

Eight spacecraft are operating at Mars as of August 2026: six orbiters and two rovers, run by NASA, ESA, the UAE, and China.^{[2][3][4][5][32]}

MAVEN is no longer on the list. NASA lost contact with the atmosphere-research orbiter on December 6, 2025 and declared its 11-year mission over on June 3, 2026.^[22] Mars Odyssey, in orbit since October 24, 2001, marked 25 years since launch in April 2026 with more than a million images returned and still serves in the relay network.^[33] Mars Reconnaissance Orbiter passed 20 years at Mars on March 10, 2026 and remains a high-resolution imager and relay.^[34] The UAE Space Agency lists Hope in an extended mission, without publishing a firm end date on its current mission page.^[3] CNSA reported in May 2026 that the Tianwen-1 orbiter remained in good health.^[4]

Several missions are planned to reinforce or extend Mars exploration:

• NASA's twin ESCAPADE small satellites, built by Rocket Lab, launched on Blue Origin's New Glenn on November 13, 2025. NASA's current trajectory calls for an Earth gravity assist in November 2026 and Mars arrival in September 2027, followed by measurements of how the solar wind interacts with the atmosphere.^[35]
• JAXA's Martian Moons eXploration spacecraft is scheduled to launch in Japanese fiscal 2026, enter Mars orbit in 2027, collect more than 10 g from Phobos, and return the sample to Australia in fiscal 2031.^[10]
• ESA's Rosalind Franklin rover is scheduled for late 2028 launch and a 2030 landing. Its drill can reach 2 m below Oxia Planum, where samples are better shielded from surface radiation. NASA is supplying the launch on a Falcon Heavy, braking engines, radioisotope heater units, and part of the analytical payload.^[36][37]

Because the relay orbiters are aging, NASA also asked industry in May 2026 for proposals for a Mars telecommunications service available no later than 2030. That is a procurement effort, not yet an operating network or a selected flight system.^[38]

Sample return and human missions#

Perseverance has sealed 27 rock cores, two regolith samples, and one atmospheric sample. Its sample system also includes witness tubes used to track contamination.^[5][39] Ten tubes were placed at a backup depot called Three Forks in January 2023; the rest remain aboard the rover.^[40]

The existing joint NASA-ESA Mars Sample Return campaign no longer has an approved implementation. Congress's fiscal 2026 agreement said it did not support the existing program and placed $110 million in a separate Mars Future Missions account.^[6] NASA's March 2026 Planetary Mission Senior Review refers explicitly to the "termination of MSR."^[5] As of August 2026, no funded mission is assigned to retrieve Perseverance's tubes.

China is pursuing a separate return campaign. CNSA says Tianwen-3 is planned for launch around 2028 and sample return around 2031.^[41] Mission chief scientist Hou Zengqian has described surface scooping, a drill reaching 2 m, and drone-assisted collection, with a goal of returning at least 500 g.^[42] These are plans, not a completed mission or a guaranteed schedule, so it is too early to say which country will return the first Mars sample.

Human missions face additional constraints. The Radiation Assessment Detector measured the particle environment during Curiosity's cruise to Mars. Researchers then extrapolated a comparable shielded, shortest-duration round-trip cruise to an effective dose of 0.66 +/- 0.12 Sv. That estimate excludes any surface stay and is not a directly measured astronaut mission dose.^[43] Mars's atmosphere is thick enough to create severe entry heating but too thin to provide all the braking needed. NASA architecture studies estimate that human-class missions would need to land payloads above 20 tonnes, more than 20 times the roughly one-tonne robotic systems demonstrated so far.^[44]

Perseverance's MOXIE experiment showed one possible way to reduce landed mass by producing 122 g of oxygen from Martian carbon dioxide across 16 runs.^[45] It was a technology demonstration, not a crew-scale life-support or propellant plant. NASA treats the Moon as a proving ground for later Mars systems, while SpaceX is developing Starship with Mars settlement as a stated goal. Neither has an approved crewed Mars mission date.

References#

1. Mars Facts - NASA Science.
2. Mars Relay Network - NASA Science, updated June 2026.
3. Emirates Mars Mission - UAE Space Agency.
4. Tianwen-1 orbiter observes interstellar object 3I/ATLAS - China National Space Administration, May 20, 2026; reports the orbiter in good health.
5. 2026 Planetary Missions Senior Review final report - NASA, March 2026.
6. Consolidated Appropriations Act, 2026 joint explanatory statement - Congressional Record, January 8, 2026.
7. Overview of the magnetic properties experiments on the Mars Exploration Rovers - Madsen et al., Journal of Geophysical Research: Planets 114, 2009; USGS Publications Warehouse.
8. Detection of ferrihydrite in Martian red dust records ancient cold and wet conditions on Mars - Valantinas et al., Nature Communications 16, article 1712, February 25, 2025.
9. Mars Moons - NASA Science.
10. Martian Moons eXploration - JAXA.
11. Geologic map of Mars - Tanaka et al., USGS Scientific Investigations Map 3292, 2014.
12. A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale crater, Mars - Grotzinger et al., Science 343, 2014.
13. Carbonate formation and fluctuating habitability on Mars - Kite et al., Nature 643, 60-66, 2025.
14. Redox-driven mineral and organic associations in Jezero Crater, Mars - Hurowitz et al., Nature 645, 332-340, September 2025.
15. Spatially distributed complex organic matter detected in an ancient river valley in Jezero crater, Mars - Murphy et al., Science Advances 12, eadx0047, June 24, 2026.
16. Ancient ocean coastal deposits imaged on Mars - Li et al., Proceedings of the National Academy of Sciences 122(9), February 24, 2025.
17. Manganese (hydr)oxides record the dynamic evolution of a million-year Hesperian ocean in Utopia Planitia, Mars - Hou et al., Nature Communications 17, article 6436, May 13, 2026.
18. SWIM Map Shows Subsurface Water Ice on Mars - NASA Science.
19. Evidence of shallow subsurface ice at Tianwen-1 landing site - Meng et al., Earth and Planetary Science Letters, 2026.
20. Liquid water in the Martian mid-crust - Wright, Morzfeld and Manga, Proceedings of the National Academy of Sciences 121(35), August 12, 2024.
21. Results from the InSight Mars mission do not require a water-saturated mid crust - Jakosky, Proceedings of the National Academy of Sciences 122(11), March 18, 2025.
22. NASA Says Farewell to MAVEN Mars Mission, Hosts Media Call Today - NASA, June 3, 2026.
23. Questioning the reliability of methane detections on Mars by the Curiosity rover - Viscardy, Catling and Zahnle, Journal of Geophysical Research: Planets 130(4), 2025.
24. Mars exploration science goals - NASA Science, updated June 23, 2026.
25. Data from detection of organics in a rock on Mars - NASA Science.
26. What is a potential biosignature? - NASA Science.
27. Mars exploration mission timeline - NASA Science.
28. Could this be the Mars Soviet 3 lander? - NASA Science.
29. Viking 1 - NASA Science.
30. 25 years of continuous robotic Mars exploration: From Pathfinder to Perseverance - NASA, July 27, 2022.
31. What it takes to get us to Mars and back - NASA, updated 2026.
32. Curiosity science updates - NASA Science, updated July 2026.
33. Odyssey celebrates 25 years - NASA Science, April 2026.
34. Mars Reconnaissance Orbiter - NASA Science.
35. NASA's ESCAPADE ready to study space weather from Earth to Mars - NASA Science, 2026.
36. ExoMars Rosalind Franklin - European Space Agency.
37. NASA begins implementation for ESA's Rosalind Franklin mission to Mars - NASA Science, April 16, 2026.
38. NASA draws on industry for Mars telecommunications network - NASA, May 14, 2026.
39. Mars rock samples - NASA Science.
40. WATSON documents final tube dropped at Three Forks sample depot - NASA Science, January 30, 2023.
41. China's Mars sample-return mission targets launch around 2028 - China National Space Administration, May 2025.
42. China's Tianwen-3 Mars sample-return mission targeted for 2031 - Academic Divisions of the Chinese Academy of Sciences, July 2, 2025, reporting remarks by chief scientist Hou Zengqian.
43. Measurements of energetic particle radiation in transit to Mars on the Mars Science Laboratory - Zeitlin et al., Science 340, 1080-1084, 2013.
44. Mars entry, descent, and landing challenges - NASA, 2024.
45. Perseverance science highlights - NASA Science.