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.

	Phobos	Mars
Discovered By	A. Hall	Known by the Ancients
Date of Discovery	1877	Unknown
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
Volume	5,729 km3	163,115,609,799 km3
Mass	10,658,529,896,187,200 kg	641,693,000,000,000,000,000,000 kg
Density	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
Mean Orbit Velocity	7696.7 km/h	86,677 km/h
Orbit Eccentricity	0.0151	0.0933941
Orbit Inclination to Ecliptic	1.075 degrees	1.85 degrees
Orbit Circumference	58,907.79 km	1,429,085,052 km