What are Phobos and Deimos?
Phobos and Deimos are Martian moons. They are among the smallest known moons in the solar system, with mean diameters of 22.2 km and 12.6 respectively. Phobos orbits extremely close to the Martian surface, with an altitude of only 6000 km (3728 mi). This is elevated in comparison to say, the International Space Station, which orbits about 350 km (217 mi) above the Earth’s surface, but it is the closest-orbiting moon of any major planet yet known. Phobos orbits Mars every seven and a half hours, compare to the International Space Station orbiting Earth every hour and a half. From the Martian surface, Phobos can be observed transiting the Sun, covering about 20% of the disc. Deimos, similar size to Phobos but significantly more distant, orbiting 23,460 km (14,577 mi) above the Martian surface, only appears as a black dot transiting the Sun, which it does regularly. Both transit events have been observed by rovers on the surface of Mars. Phobos and Deimos are not massive enough to be in h
