Astronomy Picture of the Day
Discover the cosmos! Each day we feature a different image or photograph
of our fascinating universe, along with a brief explanation written by a
October 2, 1995
Phobos: Doomed Moon of Mars
Mars, the red planet named for the Roman god of war, has two tiny moons,
whose names are derived from the Greek for Fear and Panic.
moons may well be captured
in the asteroid belt between
Mars and Jupiter
or perhaps from even more
distant reaches of the Solar System.
In this 1977 Viking orbiter image, the largest moon,
Phobos, is seen to be a heavily cratered asteroid-like object.
It is about 17 miles across and zips through the Martian sky completing an
orbit in less than 8 hours. Phobos is doomed. It orbits so close to Mars,
(about 3,600 miles above the surface compared to 250,000 miles for our
that gravitational tidal forces are dragging it down. In 100 million
years or so it could crash into the surface or be shattered by stress
caused by the relentless tidal forces, the debris forming a ring around
Tomorrow's picture: Deimos: Small Martian Moon
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