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Solar System Exploration
Phobos: Facts & Figures
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Discovered By
A. Hall
Date of Discovery
Orbit Size Around Mars (semi-major axis)
Metric: 9,376 km
English: 5,826 miles
Periapsis (closest)
Metric: 9,234 km
Apoapsis (farthest)
Metric: 9,518 km
Sidereal Orbit Period (Length of Year)
0.000873101 Earth years
0.3189 Earth days
Orbit Circumference
Metric: 58,907.79 km
Average Orbit Velocity
Metric: 7696.7 km/h
Orbit Eccentricity
Orbit Inclination
1.075 degrees
Mean Radius
Metric: 11.1 km
By Comparison: 13.4 x 11.2 x 9.2 km, potato shape
Equatorial Circumference
Metric: 69.7 km
Metric: 5,729 km3
Metric: 10,658,529,896,187,200 kg
Scientific Notation: 1.0659 x 1016 kg
Metric: 1.872 g/cm3
Surface Area
Metric: 1,548.30 km2
Surface Gravity
Metric: 0.0057 m/s2
Escape Velocity
Metric: 41 km/h
English: 25 mph
Scientific Notation: 11 m/s
Sidereal Rotation Period (Length of Day)
0.3189 Earth days
7.65 hours
By Comparison: Synchronous with orbital period
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Last Updated: 12 Aug 2013