A moon for Mars! Asaph Hall finds Phobos 149 years ago
On this date in 1877, astronomer Asaph Hall discovered a moon for Mars: Phobos, the larger of 2 moons. He discovered the other moon, Deimos, later that year. The post A moon for Mars! Asaph Hall finds Phobos 149 years ago first appeared on EarthSky .
On August 17, 1877, American astronomer Asaph Hall discovered the first known moon of Mars. The larger of Mars' two moons, Phobos, has a mean diameter of about 14 miles (22.5 km). However, despite its size, Phobos has very weak gravity, which prevents it from assuming a spherical shape like Earth's moon. Phobos' oblong surface is marked by many small craters and a large one, named Stickney after Asaph Hall's wife, Angeline Stickney.
Stickney resembles a giant hole on one end of Phobos, potentially indicating that the moon narrowly escaped destruction when it was formed.
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