Mars

Mars is the fourth planet from the Sun, a cold desert world about half Earth's diameter with a day only 37 minutes longer than our own. Iron oxide dust gives it its rust color. Billions of years ago it 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, and the long-planned Mars Sample Return campaign was cancelled in early 2026, leaving carefully sealed rock cores waiting on the surface. 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. 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.

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 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]

Atmosphere and climate#

The 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.^[2] One puzzle remains open: Curiosity measures faint, seasonally varying methane at the surface, yet Europe's Trace Gas Orbiter finds almost none higher up.

Exploration history#

Mariner 4 performed the first 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 and 2 landed in 1976; 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 1.9 km before entering hibernation in May 2022 ahead of winter; dust buildup on its solar panels apparently prevented it from ever waking, and it has not responded since.^[3][4]

The fleet at Mars in 2026#

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] The UAE has extended Hope's mission through 2028.^[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 looping through deep space ahead of a September 2027 arrival to study how the solar wind erodes the Martian atmosphere.^[6]

Sample return and human missions#

Perseverance has filled more than 30 titanium sample tubes, ten of which sit at the Three Forks depot as a backup cache. The joint NASA-ESA Mars Sample Return campaign designed to retrieve them ran into independent cost estimates approaching 11 billion dollars. The administration's fiscal 2026 budget request proposed cancelling it, and the appropriations act passed in January 2026 confirmed the cancellation even as it restored most of NASA's science funding, providing 110 million dollars for a new "Mars Future Missions" technology line intended to enable a cheaper retrieval someday.^[7][8] The samples remain on Mars. China's Tianwen-3 mission, targeted for launch around 2028, now aims to be the first to bring Martian material to Earth.

Human missions 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. Zhurong (rover) - Wikipedia.
4. Tianwen-1 and Zhurong, China's Mars orbiter and rover - The Planetary Society.
5. UAE Space Agency extends Emirates Mars Mission to 2028 - SatellitePro ME.
6. New Glenn launches NASA's ESCAPADE Mars mission, lands booster - SpaceNews.
7. Congress saves NASA budget, kills Mars sample mission - The Register.
8. You just saved NASA's budget - The Planetary Society.