Moons Of The Terrestrial Planets

1493 Words6 Pages
Moons of the Terrestrial Planets 2.2. Moons of Mars 2.2.1 Introduction Mars orbits at a distance of 1.52 AU from the Sun. Mars has two natural satellites, discovered by Asaph Hall in 1877. The innermost of these, Phobos, is about 22.2 km in diameter (27.0×21.6× 18.8) and orbits the planet with a period far less than Mars 's period of rotation 7.7 hr. (only one quarter that of Deimos), causing it to rise in the west and set in the east(Born & Duxbury 1975). Thus, it makes more than 3 orbits in a single Martian day. As it orbits, it slowly spirals in towards the Martian surface. Phobos is drawing closer to Mars by 2 meters every one hundred years, and it is predicted that it will collide with the planet /or destroyed in the atmosphere. Phobos has a semi-major axis 9376 km (2.76 Mars radii), eccentricity 0.0152 and orbit mean inclination 1.1o (relative to Mars’ equator). The outer satellite, Deimos, is about 12.6 km in diameter (15.0×12.2× 11.0) and orbital period about 30 hr. In fact, Deimos is the smallest known moon in the Solar System. Like our own Moon, Deimos orbits far enough away from Mars that it is being, slowly pushed farther and farther away from the planet. Deimos has a semi-major axis 23463.2 km (6.92 Mars radii), eccentricity 0.0003 and orbit mean inclination 2.4o (relative to Mars’ equator). Both Deimos and Phobos have very circular orbits, which lie almost exactly in Mars 's equatorial plane. They are both small, irregular objects comparable in size to the
Open Document