
Mars is a rocky planet in our solar system, often used as a mass reference for exoplanets.Mars is the fourth planet from the Sun and the second smallest in the solar system, with a mass about one-tenth that of Earth. In planetary science, it serves as a convenient reference point for rocky planets, particularly when comparing exoplanets: astronomers often describe a super-Earth as 'a few Mars masses' or 'several times Mars's mass' to give a sense of scale. Mars is also a prime target for studying planetary evolution, as its surface preserves a record of dramatic climate shifts and geological activity.
The first accurate measurement of Mars's mass came in 1877 when Asaph Hall discovered its moons and used their orbits to calculate the planet's gravitational pull. Earlier estimates, based on perturbations of Earth's orbit, had been rough but roughly correct.
Mars's mass is determined from the orbits of its two small moons, Phobos and Deimos, using Kepler's laws of motion. Its rocky composition, with a core of iron and sulfur, a silicate mantle, and a thin crust, is inferred from spacecraft measurements of its gravity field and the composition of meteorites that originated on Mars. The planet's low surface gravity (about 38% of Earth's) means it retains only a thin atmosphere, mostly carbon dioxide, and its surface pressure is too low for liquid water to persist today.
Mars serves as a calibration standard for exoplanet masses, and its geology and climate history inform models of habitability on rocky worlds elsewhere. It is also the target of ongoing robotic exploration missions.
Mars's mass is so small that a person weighing 100 kg on Earth would weigh only 38 kg there, yet the planet still has the largest volcano in the solar system, Olympus Mons, which is about 22 km high.























