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Comparison Chart
Comparison: Phobos vs. Mars

This chart shows the differences between Phobos and Mars. To change the planets/moons being compared, change one or more of the form fields at the bottom and click Refresh.

Discovered By
A. Hall
Known by the Ancients
Date of Discovery
Average Orbit Distance
9,376 km
227,943,824 km
Perihelion/Perigee (closest)
9,234 km
206,655,215 km
Aphelion/Apogee (farthest)
9,518 km
249,232,432 km
Equatorial Radius
11.1 km
3,389.5 km
Equatorial Circumference
69.7 km
21,296.9 km
5,729 km3
163,115,609,799 km3
10,658,529,896,187,200 kg
641,693,000,000,000,000,000,000 kg
1.872 g/cm3
3.934 g/cm3
Surface Area
1,548.30 km2
144,371,391 km2
Equatorial Surface Gravity
0.0057 m/s2
3.71 m/s2
Escape Velocity
41 km/h
18,108 km/h
Rotation Period (Length of Day)
0.3189 sidereal days
1.026 sidereal days
Orbit Period (Length of Year)
0.000873101 sidereal years
1.8808476 sidereal years
Mean Orbit Velocity
7696.7 km/h
86,677 km/h
Orbit Eccentricity
Orbit Inclination to Ecliptic
1.075 degrees
1.85 degrees
Orbit Circumference
58,907.79 km
1,429,085,052 km


New planets/moons to compare:

System of measurement:

Compare All Eight Planets

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Last Updated: 30 Aug 2014