| Name |
Diameter(s)
(km) |
Mean Distance
From Planet
(km) |
Rotational
Period
(days) |
Orbital
Period
(days) |
Orbital
Inclination |
Orbital
Eccentricity |
Albedo
(%) |
|---|
| Phobos |
26.8 × 18.4 |
9,378 |
0.31891 |
0.31891 |
1.08° |
0.0151 |
7 |
| Deimos |
15 × 10.4 |
23,459 |
1.26244 |
1.26244 |
1.79° |
0.0005 |
8 |
Name
The two satellites of Mars have names meaning "fear" and "terror", the traditional companions of Mars, the god of war.
Diameter
The satellites of Mars are so small that they do not have enough gravitational forces to make them spherical. They are shaped like potatoes.
Mean Distance From Planet
The satellites of Mars are very close to the planet.
Rotational and Orbital Periods
Most satellites rotate in the same period as they revolve around the planet. This is called Synchronous Rotation and is caused by the strong tidal forces exerted by the planet on the satellite. The Earth's Moon has synchronous rotation so we only see one side from the Earth.
Phobos orbits Mars in less time than the period of Mars' rotation. This means that from the surface of Mars, Phobos will appear to rise in the West and set in the East several times during a Martian day.
Orbital Inclination
This is the angle of inclination of the satellite orbits compared to the planet's equatorial plane. Note that the Earth's Moon revolves almost in the same plane as the Earth's orbit which is inclined to the Earth's equator by about 23°.
Orbital Eccentricity
The orbits of most objects in the Solar System are ellipses. This curve resembles a flattened circle. The eccentricity describes how much the ellipse differs from a circle. An orbit with an eccentricity of 0 is a circle. An orbit with an eccentricity of 1 would be an open curve called a parabola. The satellites of Mars orbit in nearly circular paths around the planet.
Albedo
This is the percentage of sunlight that is reflected by the satellites. These bodies are very dark.
