Mars has two moons, Phobos and Deimos. They are very different than our moon in more ways than one. Our Moon orbits Earth at an angle, while Mars’ moons orbit about the planet’s equator. Our Moon is 3474 km across, making it nearly a quarter of Earth’s size. Phobos is about 25 km across, and Deimos is about 10 km across; comparable in size to down town Baton Rouge. Our Moon takes 27 Earth days to orbit one time, Mars’ moons orbit much faster. Phobos, the larger and closer of the two, orbits quickly, circling Mars once every eight hours. Deimos, the smaller and farther of the two, orbits slower, circling once every 30 hours. From the point of view of a person or robot on the surface of Mars, Phobos eclipses Deimos frequently. This is because the two moons orbit in nearly the same plane.
Last week this was photographed for the first time by Curiosity. The spacecraft took a series of images, a sort of timelapse, that scientists here on Earth made into a short movie. Phobos looks vastly larger than Deimos, this is merely because it is closer.
- NASA Rover Gets Movie as a Mars Moon Passes Another (spacefellowship.com)
- NASA’s Curiosity Rover catches images of Mars’ Moons Phobos, Deimos (clarksvilleonline.com)