Mars, in astronomy: Satellites of Mars

Mars has two natural satellites, discovered by Asaph Hall in 1877. The innermost of these, Phobos, is about 7 mi (11 km) in diameter and orbits the planet with a period far less than Mars's period of rotation (7 hr 39 min), causing it to rise in the west and set in the east. The outer satellite, Deimos, is about 4 mi (6 km) in diameter.

Sections in this article:

• Introduction
• Satellites of Mars
• Astronomical Characteristics
• Seasonal Changes
• Surface Features
• Physical Characteristics
• Bibliography

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