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.^[26] Iron oxide dust gives it its rust color. Billions of years ago Mars had rivers, lakes, and perhaps seas; today its water survives as polar ice, buried glaciers, and traces of vapor in a thin carbon dioxide atmosphere. No other planet has been examined so closely.

As of mid-2026 six orbiters and two NASA rovers are working at Mars, a fleet that shrank when the MAVEN orbiter fell silent in late 2025. The long-planned Mars Sample Return campaign was never formally cancelled, but it lost its funding in January 2026, leaving carefully sealed rock cores waiting on the surface with no approved ride home. Crewed missions remain a stated long-term goal of NASA and of private ventures, but every serious study puts them years of hard engineering away.

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.^[26] 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. The planet lost its global magnetic field billions of years ago, retaining only patches of crustal magnetism, and it is orbited by two small, lumpy moons, Phobos and Deimos, each less than 23 km across.

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.^[23] Whether the two are captured asteroids or debris that reaccreted after a large impact is still unsettled, and it is the question JAXA's Martian Moons eXploration mission was designed to answer by bringing a piece of Phobos home.^[17]

Olympus Mons and Valles Marineris#

Mars holds 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 grew so large because Mars lacks plate tectonics, letting lava pile over a stationary hotspot for billions of years. It stands at the edge of the Tharsis bulge, which carries three more giant volcanoes. To the east, the Valles Marineris canyon system stretches more than 4,000 km, about a fifth of the planet's circumference, and plunges up to 7 km deep. It probably opened as a tectonic rift alongside Tharsis and was widened by landslides and, in places, by water.

Evidence for ancient water#

Orbital imagery of Mars shows branching valley networks, giant outflow channels, and river deltas, while spectrometers on the European Space Agency's Mars Express and NASA's Mars Reconnaissance Orbiter mapped clays and sulfate salts that form in liquid water. Surface missions confirmed the story. Opportunity found hematite spherules and acid-lake minerals; Curiosity showed that Gale crater held a long-lived freshwater lake about 3.5 billion years ago and detected organic molecules in its mudstones. Perseverance has been sampling an ancient river delta in Jezero crater since 2021. In September 2025 its science team reported in Nature that a mudstone called Cheyava Falls, drilled where a river once entered the crater, preserves mineral textures classed as a potential biosignature, while cautioning that non-biological chemistry has not been ruled out.^[1]

The case for a northern ocean has sharpened as well. China's Zhurong rover, driving south across Utopia Planitia toward a proposed ancient shoreline, used its ground-penetrating radar to image 76 buried layers 10 to 35 m down along a 1.3 km stretch of its route, all dipping north at 6 to 20 degrees. Writing in the Proceedings of the National Academy of Sciences in February 2025, the team read that geometry as coastal sediment built outward by waves and tides rather than laid down by rivers or lava.^[9] A study published in Nature Communications in May 2026 trained a deep learning classifier to pick manganese minerals out of infrared spectra from Zhurong and from the OMEGA and CRISM orbital spectrometers, and found manganese oxides concentrated in a narrow band of elevations in the same region, rising from 2.7 to 7.4 percent by weight over about 10 vertical meters before falling away again.^[10][25] On Earth those minerals precipitate where water meets air, and the authors interpret the band as a tidemark left by standing water that lasted 0.8 to 1.5 million years in the Hesperian period.^[10]

Water beneath the surface#

Mars did not lose all of its water. Both polar caps are largely water ice, and radar and thermal data from Mars Reconnaissance Orbiter, Mars Odyssey, and the retired Mars Global Surveyor have been combined into maps of buried ice running from the equator up to 60 degrees north, picking out mid-latitude deposits shallow enough for a future crew to mine.^[14] How much sits deeper is contested. A 2024 analysis of seismic velocities recorded by NASA's InSight lander concluded that fractured igneous rock roughly 11.5 to 20 km down is saturated with liquid water, which, if the site is typical, would be enough to cover the planet 1 to 2 km deep.^[11] The result rests on assumptions about pore shape and mineral composition, and a 2025 comment in the same journal argued that the seismic and gravity data do not require a wet mid-crust at all.^[12] Either way, nothing at that depth is within reach of any drill yet flown.

Atmosphere and climate#

Mars's atmosphere is 95 percent carbon dioxide at a surface pressure near 6 millibars, less than 1 percent of Earth's, too thin for liquid water to persist on the surface today. Dust storms occur every year and occasionally merge into planet-circling events; the 2018 global storm ended the solar-powered Opportunity rover's mission. Isotope measurements by the MAVEN orbiter showed that the solar wind stripped away most of the original atmosphere after the planet's magnetic dynamo died, turning a warmer, wetter Mars into today's desert. The same mission made the first direct observation of sputtering at Mars, in which particles accelerated by the solar wind knock gas molecules clear off the top of the atmosphere.^[2] One puzzle remains open: Curiosity measures faint, seasonally varying methane at the surface, punctuated by occasional spikes, yet Europe's Trace Gas Orbiter has never detected any from orbit. A 2025 reanalysis in the Journal of Geophysical Research: Planets argued that the fault may lie with the rover rather than the atmosphere, pointing to methane sitting in the spectrometer's foreoptics chamber at three to four orders of magnitude above the levels reported from its sample cell, and to unexplained pressure changes inside the instrument. The authors stop short of calling the detections artifacts and propose an experiment that would separate a Martian signal from an instrumental one.^[13]

Exploration history#

Mariner 4 performed the first Mars flyby in July 1965, returning 21 grainy images of a cratered surface. Mariner 9 became the first orbiter of another planet in 1971 and revealed the volcanoes and canyons hidden beneath a dust storm. NASA's Viking 1 made the first fully successful Mars landing on July 20, 1976,^[27] and Viking 2 followed later that year; their life-detection experiments produced ambiguous results now generally read as negative. After a 20-year landing gap, Pathfinder and its Sojourner rover arrived in 1997, followed by the rovers Spirit and Opportunity in 2004, the Phoenix polar lander in 2008, Curiosity in 2012, and the InSight seismic station, which recorded more than 1,300 marsquakes between 2018 and 2022. India's ISRO operated its first Mars orbiter from 2014 to 2022.

February 2021 brought three arrivals in one month: the United Arab Emirates' Hope orbiter, NASA's Perseverance with the Ingenuity helicopter, which flew 72 times before retiring in January 2024, and the CNSA's Tianwen-1 orbiter with the Zhurong rover, the first non-American rover to operate on Mars. Zhurong drove about 1,921 m before pausing for winter dormancy on May 18, 2022.^[3] Dust buildup on its solar panels apparently prevented it from ever waking: it did not resume work that December as planned, and orbital images taken in February 2023 showed it stationary.^[4]

The fleet at Mars in 2026#

Eight spacecraft are operating at Mars in mid-2026: six orbiters and two rovers, run by NASA, ESA, the UAE, and China.

MAVEN is no longer on the list: NASA lost contact with the atmosphere-research orbiter on December 6, 2025 and, after months of recovery attempts, declared the 11-year mission over on June 3, 2026.^[2] What remains is an elderly fleet that keeps working. Mars Odyssey, in orbit since October 24, 2001, marked 25 years since launch in April 2026 with more than a million images behind it, and remains part of the relay network that carries rover data back to Earth.^[16] Mars Reconnaissance Orbiter passed 20 years at Mars on March 10, 2026 and remains the main high-resolution camera and relay in the system.^[15] In February 2026 the UAE added three years to Hope's mission, extending it to 2028 after the spacecraft returned more than 10 terabytes of data against a one-terabyte goal.^[5]

Reinforcements are coming. NASA's twin ESCAPADE smallsats, built by Rocket Lab, launched on Blue Origin's New Glenn rocket on November 13, 2025 and are loitering near the Earth-Sun L2 point, waiting on a trans-Mars injection burn planned for November 2026 and an arrival in September 2027, after which they will measure how the solar wind erodes the Martian atmosphere.^[6] JAXA's Martian Moons eXploration probe is set to launch in Japanese fiscal 2026, reach Mars orbit in 2027, and return more than 10 grams of Phobos to Australia in 2031.^[17] ESA's Rosalind Franklin rover, stranded when its Russian launch was cancelled in 2022, has a ride again: NASA began implementation in April 2026 for a launch no earlier than late 2028 on a Falcon Heavy, with NASA providing the launch, the landing platform's braking engines, radioisotope heater units, and a mass spectrometer for the rover's organic molecule analyzer. The rover is built to drill two meters into Oxia Planum in search of subsurface signs of past or present life.^[18]

Sample return and human missions#

NASA's Perseverance rover carries 43 ultraclean titanium tubes and has used 33 of them: 30 of the 38 reserved for samples, holding 27 rock cores, two scoops of loose regolith, and one tube of Martian air, plus three of the five witness tubes that record contamination brought from Earth.^[19] Ten of those tubes lie in a zig-zag pattern at a flat site called Three Forks, laid down in January 2023 as a backup cache in case the rover could not deliver the rest itself.^[20]

The joint NASA-ESA Mars Sample Return campaign designed to retrieve those samples ran into independent cost estimates approaching 11 billion dollars, and the administration's fiscal 2026 budget request proposed cancelling it. No formal termination followed; the funding simply stopped. The House and Senate appropriations agreement whose text was released on January 5, 2026 carried no line for the program, stating only that "the agreement does not support the existing Mars Sample Return (MSR) program," and set aside 110 million dollars for a new "Mars Future Missions" account, below the 300 million the House had proposed. Report language pointed that account at radar, spectroscopy, and entry, descent, and landing work inherited from MSR, while Congress otherwise rejected the deeper cuts sought for NASA science.^[7][8] The fiscal 2027 request then kept Mars Future Missions at 110 million dollars but redirected it away from sample-return technology and toward a cadence of cheaper missions, including a solicitation planned for October 2026 for a 2030 launch capped at 220 million dollars. Four senators asked appropriators in April 2026 for at least 400 million instead.^[21]

The samples therefore stay where they are, with no funded mission to collect them. China's Tianwen-3 is now the likeliest first delivery: a pair of launches in 2028 and a return to Earth in July 2031.^[22] Hou Zengqian, the mission's chief scientist, has said it will carry a drone rather than a rover, combine surface scooping, drilling two meters down, and drone-assisted grabbing, and aim to bring back at least 500 grams.^[24]

Human missions to Mars face compounding problems. A round trip takes six to nine months of transit each way plus, for most trajectories, more than a year on the surface waiting for the planets to realign. Curiosity's radiation detector measured about 0.66 sieverts for the cruise phases alone, a large share of an astronaut's career dose limit. The atmosphere is thick enough to burn arriving spacecraft yet too thin to slow them, and nothing heavier than about one tonne has ever been landed intact, far short of the 20 or more tonnes a crew would need. Progress is incremental: Perseverance's MOXIE experiment produced 122 grams of oxygen from Martian air between 2021 and 2023, the first resource extraction on another planet. NASA's Moon-to-Mars strategy treats the Moon as the proving ground, while SpaceX is developing Starship with Mars settlement as its stated purpose; no crewed mission yet has a firm date.

References#

1. A biosignature on Mars? Unpacking Perseverance's Cheyava Falls find - The Planetary Society.
2. NASA Says Farewell to MAVEN Mars Mission, Hosts Media Call Today - NASA.
3. Evidence for marine sedimentary rocks in Utopia Planitia: Zhurong rover observations - Xiao et al., National Science Review 10(9), 2023.
4. Tianwen-1 and Zhurong, China's Mars orbiter and rover - The Planetary Society.
5. UAE extends Hope probe's Mars mission to 2028 - The National, February 17, 2026.
6. New Glenn launches NASA's ESCAPADE Mars mission, lands booster - SpaceNews.
7. Great News for NASA in the House-Senate FY2026 Appropriations Report - SpacePolicyOnline, January 2026.
8. You just saved NASA's budget - The Planetary Society.
9. Ancient ocean coastal deposits imaged on Mars - Li et al., Proceedings of the National Academy of Sciences 122(9), February 24, 2025.
10. 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.
11. Liquid water in the Martian mid-crust - Wright, Morzfeld and Manga, Proceedings of the National Academy of Sciences 121(35), August 12, 2024.
12. 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.
13. Questioning the Reliability of Methane Detections on Mars by the Curiosity Rover - Viscardy, Catling and Zahnle, Journal of Geophysical Research: Planets 130(4), 2025.
14. SWIM Map Shows Subsurface Water Ice on Mars - NASA Science.
15. Mars Reconnaissance Orbiter - NASA Science.
16. Odyssey Celebrates 25 Years - NASA Science, April 2026.
17. Martian Moons eXploration - JAXA.
18. NASA Begins Implementation for ESA's Rosalind Franklin Mission to Mars - NASA Science, April 16, 2026.
19. Mars Rock Samples - NASA Science.
20. NASA's Perseverance Rover Completes Mars Sample Depot - NASA Jet Propulsion Laboratory, January 2023.
21. Senators seek increased funding for NASA Mars missions - SpaceNews, April 15, 2026.
22. Tianwen-3: China's Mars sample return mission - The Planetary Society.
23. Mars Moons - NASA Science.
24. 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.
25. Mars's manganese 'bathtub ring' reveals ancient ocean timeline and its potential for life - Phys.org, May 2026.
26. Mars Facts - NASA Science.
27. Viking 1 - NASA Science.