How many moons does Mars have?

The Red Planet, Mars, is orbited by two small natural satellites. These celestial companions are named Phobos and Deimos, after the Greek mythological twin characters who accompanied their father Ares (the Greek counterpart to the Roman god Mars) into battle. American astronomer Asaph Hall discovered both moons in August 1877.

Phobos and Deimos are quite different from Earth's relatively large, spherical moon. They are notably small and irregularly shaped, resembling asteroids more than typical moons. Phobos, the larger of the two, measures approximately 22 kilometers (14 miles) across, while Deimos is even smaller, at about 12 kilometers (8 miles) in diameter. Their surfaces are dark, heavily cratered, and covered in dust and loose rocks.

The origin of these Martian moons has been a subject of scientific debate. One prominent theory suggests that Phobos and Deimos are captured asteroids, pulled into Mars' orbit by its gravitational force. However, their stable, nearly circular orbits challenge this idea, as captured bodies typically have more erratic paths. Another hypothesis proposes that they formed from debris ejected after a massive impact on Mars itself, similar to how Earth's Moon is thought to have formed. Recent studies, including data from the United Arab Emirates' Hope spacecraft, suggest that Deimos, and potentially Phobos, might be made of rocky material similar to Mars, lending support to the impact theory.

Phobos orbits incredibly close to Mars, completing a revolution in just 7.66 hours, which means it whips across the Martian (Review) sky about three times a day. This close proximity means Phobos is slowly spiraling inward, and scientists predict that within 50 million years, it will either collide with Mars or break apart to form a ring around the planet. Deimos, orbiting further out, takes a more leisurely 30 hours to complete its circuit around Mars. These unique characteristics and their uncertain origins make Phobos and Deimos intriguing objects of study for future missions, potentially serving as valuable stepping stones for human exploration of the Red Planet.