[petuniasevan]

Phobos orbits Mars at an altitude of only about 3000 miles! Not only that, but it orbits in a retrograde motion. This is not a stable orbit in the long term. It loses about 6 feet in altitude per century; Phobos may one day reach the Roche limit and break up, perhaps forming a ring. Or else it may slam into Mars, with catastrophic results.

If you were on Mars near its equator, you would see Phobos cross the sky three times a day! If you were in one of the polar regions, Phobos would be below the horizon.

Both Phobos and Deimos seem to be captured asteroids.

The giant crater which dominates Phobos is called Stickney.

Here are Phobos' "vital statistics"

Phobos Statistics
Discovered by	Asaph Hall
Date of discovery	1877
Mass (kg)	1.08e+16
Mass (Earth = 1)	1.8072e-09
Radius (km)	13.5x10.8x9.4
Radius (Earth = 1)	2.1167e-03
Mean density (gm/cm^3)	2.0
Mean distance from Mars (km)	9,380
Rotational period (days)	0.31910
Orbital period (days)	0.31910
Mean orbital velocity (km/sec)	2.14
Orbital eccentricity	0.01
Orbital inclination (degrees)	1.0
Escape velocity (km/sec)	0.0103
Visual geometric albedo	0.06
Magnitude (Vo)	11.3

[petuniasevan]

[Joan912]

Oh my gosh, I have never even heard of Phobos! Thanks for the info! :)