Mars
Mars is the fourth planet from the Sun, a rocky planet with a mass of 6.42 × 10²³ kg (0.107× Earth), an equatorial diameter of 6,792 km, and 2 moons, orbiting 1.524 AU from the Sun.
Mars is the fourth planet from the Sun and the second-smallest planet in our solar system. Named after the Roman god of war for its blood-red appearance, Mars has captivated humanity as a potential second home. It has the tallest mountain and the deepest canyon in the entire solar system, and it is the only planet besides Earth where robotic rovers have driven across the surface.
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- Equatorial diameter
- 6,792 km
- Mass
- 6.42 × 10²³ kg
- Mass (Earth = 1)
- 0.107×
- Distance from Sun
- 1.524 AU
- Surface gravity
- 3.72 m/s²
- Average temperature
- -65°C
- Known moons
- 2
- Orbital period
- 1.9 Earth years
- Rotation period
- 24.6 hours
- Ring system
- No
Source: NASA Planetary Fact Sheets (nssdc.gsfc.nasa.gov)
Atmosphere
Thin carbon dioxide (95.3%), nitrogen (2.7%), argon (1.6%). Surface pressure less than 1% of Earth's.
In Depth
Mars is a cold, dusty desert world with a thin atmosphere that cannot support liquid water on the surface today. Yet abundant evidence, from dry river valleys to mineral deposits that form only in water, tells us Mars was once warm and wet.
Olympus Mons towers 21.9 km above the surrounding plains, nearly 2.5 times the height of Mount Everest. It is a shield volcano so wide (600 km) that an observer on its summit could not see the base, and it sits within the Tharsis bulge, a continent-sized volcanic plateau that also hosts three other giant shield volcanoes: Arsia Mons, Pavonis Mons, and Ascraeus Mons, each larger than any volcano on Earth. Valles Marineris stretches 4,000 km along the equator, up to 7 km deep and 200 km wide, and it would span the entire continental United States. Scientists believe part of it formed as the crust stretched and cracked while the Tharsis bulge grew, rather than from erosion alone. On the opposite side of the planet lies Hellas Basin, one of the largest and deepest confirmed impact craters in the solar system, gouged out by an asteroid strike billions of years ago. Mars has two small, irregularly shaped moons: Phobos (22 km) and Deimos (12 km), likely captured asteroids from the nearby asteroid belt. Phobos orbits so close and so fast, completing a lap every 7.6 hours, that it rises in the west and sets in the east twice each Martian day, and it is spiraling slowly inward, destined to either crash into Mars or be torn apart into a ring within about 50 million years.
The planet's thin atmosphere (less than 1% of Earth's surface pressure) means liquid water boils away almost instantly, but subsurface ice is abundant, and seasonal frost even forms at the poles. Mars experiences seasons similar to Earth because its axial tilt is nearly identical (25.2° vs 23.4°), though each season lasts roughly twice as long since a Martian year is almost double an Earth year.
Global dust storms can envelop the entire planet for months at a time, and smaller, more localized dust devils regularly scour the surface year-round. NASA's InSight lander, which operated from 2018 to 2022, used a seismometer to detect hundreds of 'marsquakes,' revealing that Mars has a surprisingly large liquid core with a radius of roughly 1,830 km.
Notable Features
- 01
Olympus Mons, the tallest volcano in the solar system at 21.9 km
- 02
Valles Marineris, a canyon system stretching 4,000 km, dwarfing the Grand Canyon
- 03
Polar ice caps made of water ice and dry ice (frozen carbon dioxide)
- 04
Evidence of ancient river channels and lake beds suggesting past liquid water
- 05
The Tharsis bulge, a volcanic plateau roughly the size of North America hosting four of the solar system's largest volcanoes
- 06
Hellas Basin, one of the largest confirmed impact craters in the solar system at about 2,300 km across and over 7 km deep
Try It Yourself
Exploration & Missions
Mars is the most explored planet beyond Earth. NASA's Mariner 4 made the first flyby in 1965. The Viking 1 lander (1976) was the first to successfully operate on the surface. Since the 1990s, a fleet of orbiters, landers, and rovers have studied Mars: Pathfinder/Sojourner (1997), Spirit and Opportunity (2004), Curiosity (2012), and Perseverance with the Ingenuity helicopter (2021).
The ESA's Mars Express has orbited since 2003, and NASA's InSight lander spent four years listening for marsquakes before its mission ended in 2022. Perseverance is currently exploring Jezero Crater, an ancient lakebed and river delta, collecting rock samples and caching them on the surface for a future Mars Sample Return mission that would bring them to Earth for lab analysis impossible to perform remotely. Along the way, Curiosity and Perseverance have both detected organic molecules and seasonal methane fluctuations: tantalizing but not conclusive clues in the ongoing search for evidence of past microbial life.
China's Zhurong rover (2021) explored Utopia Planitia before entering an extended hibernation. Human missions to Mars are actively planned by NASA and SpaceX for the 2030s, with reusable heavy-lift rockets under development specifically to make a crewed journey feasible, and proposed landing sites are already being evaluated for a combination of scientific value and access to subsurface ice that future crews could use for water and fuel production.
Fun Facts
A year on Mars lasts 687 Earth days, but a Mars day ('sol') is only 37 minutes longer than an Earth day.
Mars appears red because its surface is rich in iron oxide, essentially rust covering the entire planet.
The Opportunity rover was designed for a 90-day mission but operated for nearly 15 years (2004-2019).
Ingenuity, the Mars helicopter, was designed for 5 flights but completed over 70 before retiring.
Mars has the largest confirmed volcano and one of the largest confirmed impact craters of any rocky planet in the solar system, on opposite sides of the globe.
Phobos, Mars's larger moon, is slowly spiraling inward and is expected to eventually break apart into a ring of debris circling the planet.
Frequently Asked Questions
Could humans live on Mars?▾
Not without extensive technology. Mars has no breathable atmosphere, extreme cold (averaging -65°C), intense radiation (no magnetic field), and very low atmospheric pressure. Settlers would need pressurized habitats, radiation shielding, and either imported or locally manufactured oxygen and water. NASA and SpaceX are developing technologies to address these challenges.
Was there ever water on Mars?▾
Yes, strong evidence shows Mars once had rivers, lakes, and possibly an ocean covering much of the northern hemisphere. Minerals like clays and sulfates (which form in water) are found across the surface. The Curiosity and Perseverance rovers have explored ancient lakebeds. Mars likely lost most of its water 3-4 billion years ago as its magnetic field weakened and the solar wind stripped away the atmosphere.
Why is Mars red?▾
Mars is red because its surface rocks and dust are rich in iron oxide (Fe₂O₃), commonly known as rust. Billions of years ago, iron in Martian rocks reacted with small amounts of oxygen in the atmosphere and water, oxidizing the surface. Fine rust-colored dust gets lofted into the atmosphere, giving even the sky a butterscotch tint.
Does Mars have moons?▾
Mars has two small moons, Phobos and Deimos, both thought to be asteroids captured by Mars's gravity long ago. Phobos, the larger at about 22 km across, orbits so close to Mars that it completes a full lap every 7.6 hours. Deimos, about 12 km across, orbits much farther out and more slowly.
What did the InSight mission discover?▾
NASA's InSight lander placed a seismometer on the Martian surface from 2018 to 2022 and detected hundreds of marsquakes. The data revealed that Mars has a much larger, mostly liquid core than previously expected, roughly 1,830 km in radius, reshaping models of how rocky planets form and cool.
Learn More
The 8 Planets in Order: An Interactive Guide for Students — an in-depth article covering all 8 planets, with size comparisons and learning activities.
Data source: NASA Planetary Fact Sheets
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