Moons of Mars

Phobos and Deimos are Mars’s two small natural satellites. Both are irregularly shaped and orbit close to the planet, with Phobos completing an orbit faster than Mars rotates.

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Phobos: The larger and closer of Mars’s two moons, orbiting the planet in about 7 hours and 39 minutes. Its orbit is slowly shrinking, and it will eventually collide with Mars or break apart.
Capture hypothesis: The hypothesis that a body became a satellite after being gravitationally captured by a planet. It could explain the moons’ irregular shapes and resemblance to asteroids.
Phobos and Deimos exploration: The study of Mars’s moons using spacecraft, landers, sample-return missions, and crewed mission proposals. Their low gravity and proximity make them potential staging sites for Mars exploration.
Mariner 9: A NASA spacecraft that became the first to orbit Mars in 1971. It returned close-up images of both moons during the first successful Mars orbital mission.
Earth's Moon: Earth’s natural satellite, a large rocky body about one-quarter of Earth’s diameter. Unlike the Martian pair, it is large relative to its planet and likely formed after a giant impact.
Deimos: The smaller and more distant of Mars’s two moons, completing an orbit in about 30 hours. Its slow outward drift contrasts with Phobos’s inward spiral.
Giant impact hypothesis: The hypothesis that a large collision ejects debris that later forms moons around a planet. Impact debris could account for the moons’ nearly circular, equatorial orbits.
JAXA: Japan’s national space agency, responsible for developing and operating civilian space missions. JAXA’s Martian Moons eXploration mission is designed to study both moons and return Phobos samples.
Viking 1: A NASA Mars orbiter and lander mission that reached Mars in 1976. Its orbiter photographed the moons and improved measurements of their shapes and orbits.
Galilean moons: Jupiter’s four largest moons: Io, Europa, Ganymede, and Callisto. These large, differentiated worlds contrast with Mars’s tiny, irregular satellites.