March 30, 2026
Mars Facts: Everything We Know About the Red Planet
Mars has captivated human imagination for centuries — from ancient astronomers who tracked its reddish wandering across the night sky to the engineers who landed Perseverance in Jezero Crater. It's the most explored planet beyond Earth, with over 50 missions launched since the 1960s. Today, active rovers and orbiters send back data daily. Here's what we've learned, drawn from NASA's Planetary Fact Sheets and decades of mission science.
Photo credit: Unsplash
Mars by the Numbers
Mars is the fourth planet from the Sun, orbiting at an average distance of 227.9 million km (1.524 AU). Its equatorial diameter of 6,792 km makes it about 53% the size of Earth. Despite its smaller volume, Mars has a similar amount of dry land area to Earth because it has no oceans. Its mass is 6.417 × 10²³ kg, roughly 10.7% of Earth's, producing a surface gravity of 3.72 m/s² — about 38% of what you feel standing on Earth. A 70 kg person would weigh only 26.5 kg on Mars.
A Martian day (called a "sol") lasts 24 hours and 37 minutes — remarkably similar to Earth's day. But a Martian year is nearly twice as long: 687 Earth days. Mars also has seasons because its axial tilt of 25.19 degrees is close to Earth's 23.44 degrees. However, Mars's more eccentric orbit (0.0934 vs. Earth's 0.0167) means its seasons are unequal in length — southern hemisphere summer is shorter and more intense than northern hemisphere summer.
The Thin Red Atmosphere
Mars's atmosphere is 95.3% carbon dioxide with traces of nitrogen (2.7%) and argon (1.6%). The surface pressure averages just 0.636 kPa — less than 1% of Earth's sea-level pressure. This is below the Armstrong limit, meaning liquid water cannot exist on the surface at most temperatures; it either freezes or sublimates directly into vapor. An unprotected human would not be able to breathe — and their blood would not boil (a common myth), but the pressure is low enough that exposed saliva and moisture on the eyes would rapidly evaporate.
Despite its thinness, Mars's atmosphere produces weather. Dust devils roam the surface regularly — the Spirit rover photographed hundreds of them, some over 8 km tall. Planet-encircling dust storms occur every few Mars years, blocking sunlight for months. The 2018 global dust storm was so severe it ended the Opportunity rover's mission by coating its solar panels in opaque dust. The atmosphere also creates thin clouds of water ice crystals at altitudes around 10-30 km, especially near the equator in the afternoon.
Olympus Mons and Valles Marineris: Superlative Geology
Mars hosts the most extreme topography in the solar system. Olympus Mons is a shield volcano that rises 21.9 km above the surrounding plains — nearly 2.5 times the height of Mount Everest. Its base diameter of approximately 600 km means it would cover most of France. The caldera at the summit is 80 km wide and contains six collapse craters. Despite its immense size, Olympus Mons has such gentle slopes (averaging 5 degrees) that you could stand on it and not realize you were on a volcano — the curvature would extend beyond the horizon in every direction.
Valles Marineris is the solar system's largest canyon system. Stretching 4,000 km along the Martian equator (roughly the distance from New York to Los Angeles), it reaches depths of 7 km and widths of 200 km. For comparison, the Grand Canyon is 446 km long and 1.6 km deep. Valles Marineris wasn't carved by water like the Grand Canyon — it's a tectonic rift that opened as the Tharsis volcanic plateau uplifted billions of years ago, though water erosion may have widened it later.
Water on Mars: Past and Present
Evidence from NASA's rovers and orbiters overwhelmingly indicates that Mars once had abundant liquid water on its surface. Curiosity rover discovered rounded pebbles in an ancient streambed in Gale Crater — rocks smoothed by flowing water over extended periods. Orbital instruments have identified clay minerals (phyllosilicates) and sulfate deposits across the surface, both of which require water to form. The Mars Reconnaissance Orbiter mapped ancient river deltas, lake shorelines, and what appear to be ocean coastlines in the northern lowlands.
Today, water on Mars exists primarily as ice. The polar ice caps contain both frozen carbon dioxide ("dry ice") and water ice. The north polar cap's permanent water ice layer is roughly 1,000 km across and up to 3 km thick. NASA's Mars Odyssey orbiter and the Phoenix lander confirmed vast deposits of subsurface water ice at mid-to-high latitudes, sometimes just centimeters below the surface. ESA's Mars Express radar instrument detected what appears to be a 20-km-wide lake of liquid water beneath 1.5 km of ice at the south pole — though this finding remains debated. If confirmed, it would be the first known body of present-day liquid water on Mars.
The Search for Life
The question of whether Mars ever harbored life drives much of modern Mars exploration. The Perseverance rover, which landed in Jezero Crater in February 2021, is specifically designed to search for biosignatures — chemical or structural evidence of past microbial life. Jezero was chosen because orbital imaging shows a 3.5-billion-year-old river delta where water once flowed into a lake, depositing sediments that could have preserved organic material.
Perseverance is collecting rock core samples, sealing them in titanium tubes, and caching them on the surface for a future Mars Sample Return mission — a joint NASA-ESA effort that would bring Martian material to Earth for laboratory analysis. No previous mission has returned samples from another planet. The complexity is staggering: a fetch rover must retrieve the cached tubes, a Mars Ascent Vehicle must launch them into Mars orbit, and an Earth Return Orbiter must capture them and fly them home. The samples would be the first extraterrestrial material analyzed in Earth-based labs since Apollo.
Phobos and Deimos: Mars's Tiny Moons
Mars has two small, irregularly shaped moons. Phobos (22.2 km across) orbits just 6,000 km above the Martian surface — closer than any other known moon to its parent planet. It completes an orbit in only 7 hours and 39 minutes, rising in the west and setting in the east from the perspective of an observer on Mars. Tidal forces are gradually pulling Phobos closer; in about 50 million years, it will either crash into Mars or break apart into a ring system.
Deimos (12.4 km across) orbits much farther out at 23,460 km. Both moons are likely captured asteroids, though some models suggest they formed from debris ejected by a giant impact on Mars early in its history. JAXA's planned Martian Moons eXploration (MMX) mission aims to land on Phobos, collect samples, and return them to Earth — a mission that could settle the debate about these tiny moons' origins.
Explore More
Want to test your knowledge of Mars and the other planets? Our Solar System games challenge you to sort planets by properties, identify worlds from clues, and even land spacecraft on alien surfaces. Mars is just the beginning.
Explore Solar System Games →Sources
- NASA Planetary Fact Sheet. "Mars Fact Sheet." nssdc.gsfc.nasa.gov.
- NASA Jet Propulsion Laboratory. "Mars 2020 Perseverance Rover." mars.nasa.gov.
- ESA Space Science. "Mars Express: Subsurface Radar Observations." esa.int/Science_Exploration.