Discovery | |
---|---|
Discovered by | Asaph Hall |
Discovery date | August 18, 1877 |
Orbital characteristics | |
Epoch J2000 | |
Periapsis | 9235.6 km |
Apoapsis | 9518.8 km |
9377.2 km[1] | |
Eccentricity | 0.0151 |
0.31891023 d (7 h 39.2 min) | |
Average orbital speed | 2.138 km/s |
Inclination | 1.093° (to Mars's equator) 0.046° (to local Laplace plane) 26.04° (to the ecliptic) |
Satellite of | Mars |
Physical characteristics | |
Dimensions | 26.8 × 22.4 × 18.4 km[2] |
Mean radius | 11.1 km[3] (0.0021 Earths) |
~6100 km² (11.9 µEarths) | |
Volume | 5680 km³[4] (5.0 nEarths) |
Mass | 1.072×1016 kg[5] (1.8 nEarths) |
Mean density | 1.887 g/cm³[4] |
0.0084–0.0019 m/s² (8.4-1.9 mm/s²) (860-190 µg) | |
11.3 m/s (40 km/h)[5] | |
synchronous | |
Equatorial rotation velocity | 11.0 km/h (at longest axis' tips) |
0° | |
Albedo | 0.071[3] |
Temperature | ~233 K |
11.3[6] | |
Phobos (or Mars I) is one of Mars' moons. The other is Deimos.
Phobos is the larger of the two moons, and is only 27 kilometers in diameter. This is about as far as a car can travel on the highway in 15 minutes. It is covered with craters, as Earth's moon is.[7]
It is named after the god Phobos in Greek mythology. Its name means "fear".
Phobos is trapped in tidal drag, with its orbit lowering roughly 1.8 meters per century. In about 50 million years, Phobos will reach the Roche limit, where it is likely to be torn apart. Some fragments will fall on Mars and some will form a planetary ring or rings around Mars.
The other moon, Deimos, is the smaller of the two.
The Soviet Union sent at least two space craft to this moon, Phobos 1 and Phobos 2. Both failed or lost contact with Earth, but Phobos 2 managed to take some pictures of the moon in 1989 before dying.
There is one large crater on Phobos called Stickney. It is the size of the moon itself.