March 30, 2026
Mars Facts: Everything You Need to Know About the Red Planet
Mars is the fourth planet from the Sun and the most explored world beyond Earth. Named after the Roman god of war for its blood-red appearance, 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. With over 50 missions launched since the 1960s, active rovers and orbiters send back new data daily. This complete guide covers everything we know about Mars: its size, diameter, surface area, physical features, atmosphere, water, moons, and the ongoing search for life — all drawn from NASA's Planetary Fact Sheets and decades of mission science.
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Mars Fact File
How Big Is Mars?
Mars is the second-smallest planet in our solar system, larger only than Mercury. Its equatorial diameter is 6,792 km (4,221 miles) — about 53% the width of Earth. If you placed Mars next to Earth, you could fit almost seven Mars-sized spheres inside Earth's volume. The polar diameter is slightly smaller at 6,752 km because, like all rotating bodies, Mars bulges slightly at the equator.
The surface area of Mars is 144.8 million km² (55.9 million square miles). Here's a striking comparison: since Mars has no oceans, all of that surface is dry land — and Earth's total land area is 148.9 million km². Mars's dry land is nearly equal to every continent on Earth combined. 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.
Mars by the Numbers
Mars orbits the Sun at an average distance of 227.9 million km (1.524 AU). A Martian day — called a "sol" — lasts 24 hours and 37 minutes, remarkably close to an Earth day. But a Martian year is nearly twice as long: 687 Earth days. Mars 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.
Mars reaches its closest approach to Earth approximately every 26 months during opposition, when the two planets line up on the same side of the Sun. At its nearest, Mars comes within about 55.7 million km of Earth; at its farthest, it's over 400 million km away. These close approaches create launch windows for spacecraft, which is why Mars missions tend to cluster in roughly two-year intervals.
Why Is Mars Red?
Mars earns its nickname "the Red Planet" from its iron-rich surface. Billions of years ago, iron in Martian rocks and soil reacted with trace oxygen in the atmosphere, creating iron oxide — essentially rust. This reddish-brown dust blankets most of the surface in a layer just millimeters thick, yet it's enough to color the entire planet. During dust storms, fine particles are lofted tens of kilometers into the atmosphere, giving the Martian sky its characteristic butterscotch hue during the day and blue-tinted sunsets in the evening.
Not all of Mars is uniformly red. NASA's rovers have revealed a surprising variety of surface colors: dark basaltic rocks, grey sand dunes, light-toned mineral outcrops, and even patches of olive-green olivine crystals. The iron-oxide coating is a surface veneer — beneath it, Martian geology is as varied as Earth's.
Physical Features of Mars
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 standing on it, you wouldn't 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 New York to Los Angeles), it reaches depths of 7 km and widths of 200 km — dwarfing the Grand Canyon (446 km long, 1.6 km deep). Valles Marineris is a tectonic rift that opened as the Tharsis volcanic plateau uplifted billions of years ago, though water erosion may have widened it later.
The Tharsis Bulge is a massive volcanic plateau roughly 4,000 km across and 10 km above the mean surface elevation. It contains three enormous shield volcanoes — Ascraeus Mons, Pavonis Mons, and Arsia Mons — aligned in a chain, each exceeding 14 km in height. On the opposite side of the planet, Hellas Planitia is one of the largest impact basins in the solar system: 2,300 km across and 7 km deep. Its floor has the highest atmospheric pressure on Mars — thick enough that liquid water could theoretically persist briefly under the right temperature conditions.
Mars's two polar ice caps are also major surface features. The north polar cap (Planum Boreum) is roughly 1,000 km across and up to 3 km thick, composed primarily of water ice with a seasonal coating of CO&sub2; frost. The south polar cap (Planum Australe) retains a permanent layer of frozen carbon dioxide year-round, making it visually brighter and colder. Together, the polar caps store enough water ice that, if melted, it could cover the entire planet in a layer roughly 35 meters deep.
Mars Surface and Terrain
One of Mars's defining physical features is the crustal dichotomy: the planet is split into two dramatically different hemispheres. The southern highlands are ancient, heavily cratered terrain sitting 1–3 km above the mean elevation — some of the oldest surfaces in the solar system at 3.8–4.1 billion years old. The northern lowlands are younger, smoother plains sitting well below the mean elevation, with far fewer craters. The boundary between the two is one of the most debated features in planetary science — it may be the scar of a massive ancient impact or the result of internal convection processes.
Surface temperatures on Mars vary dramatically. The average temperature is a frigid −63 °C (−81 °F), but this ranges from around −140 °C at the winter poles to a comparatively mild 20 °C (68 °F) at the equator during summer afternoons. The thin atmosphere provides almost no insulation, so temperatures can swing by 70°C or more between day and night at the same location. The soil is rich in perchlorates — chlorine-based salts that lower the freezing point of water and could play a role in possible subsurface brine formation.
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.
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.
Frequently Asked Questions About Mars
▶What is the size of Mars?
Mars has an equatorial diameter of 6,792 km (4,221 miles), making it about 53% the size of Earth. Its total surface area is 144.8 million km² — roughly equal to Earth's total dry land area. Mars is the second-smallest planet in our solar system, larger only than Mercury.
▶What is the diameter of Mars in km?
The equatorial diameter of Mars is 6,792 km (4,221 miles). The polar diameter is slightly smaller at 6,752 km due to the planet's rotation. For comparison, Earth's equatorial diameter is 12,756 km — about 1.88 times wider than Mars.
▶What is the surface area of Mars?
Mars has a total surface area of 144.8 million km² (55.9 million square miles). Since Mars has no oceans, all of this is dry land — which is remarkably close to Earth's total land area of 148.9 million km². You could fit all of Earth's continents on Mars with room to spare.
▶What are the main physical features of Mars?
Mars's major physical features include Olympus Mons (the tallest volcano in the solar system at 21.9 km), Valles Marineris (a 4,000 km canyon system), the Tharsis Bulge (a massive volcanic plateau), Hellas Planitia (a 2,300 km wide impact basin), and polar ice caps made of water ice and frozen carbon dioxide.
▶How big is Mars compared to Earth?
Mars is roughly half the size of Earth. Its diameter is 53% of Earth's, its mass is 10.7% of Earth's, and its surface gravity is 38% of Earth's. However, Mars has almost the same amount of dry land because it has no oceans. A 70 kg person would weigh only 26.5 kg on Mars.
▶Why is Mars red?
Mars appears red because its surface is rich in iron oxide (rust). Billions of years ago, iron in Martian rocks reacted with oxygen in the atmosphere, creating a layer of reddish dust that covers most of the surface and gets lofted into the atmosphere during dust storms, giving the sky a butterscotch hue.
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.
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.
- NASA Science. "Mars: Facts." science.nasa.gov/mars/facts.
- USGS Astrogeology. "Mars Global Surveyor: MOLA Topography." astrogeology.usgs.gov.