Did you know? Phobos and Deimos

This Month Elizabeth Cocking features Phobos and Deimos. The moons of Mars. Not your average moon.

Phobos and Deimos are not your typical moons and bear more resemblance to asteroids. They have meteorite-like compositions and irregular shapes.

Both moons are incredibly small. Phobos is only 22 kilometres in diameter, while Deimos, is only 12 kilometres in diameter, making them among some of the smallest moons in the solar system. Both moons were discovered in 1877 by American astronomer Asaph Hall. Deimos on 12th August and Phobos on 18th August 1877.

The image left is of Phobos. It was taken by the Mars Reconnaissance Orbiter in 2008. CREDIT: NASA / JPL-Caltech / University of Arizona - http://photojournal.jpl.nasa.gov/catalog/PIA10368

The names Phobos, which means Fear, and Deimos which means Panic, come from Greek mythology. They are the sons of Ares, the god of war.

Phobos is slowly spiralling toward Mars at a rate of 1.8 metres every century. Within 50 million years the moon will either collide with Mars or become a ring of rubble around it. Data from the Mars rovers confirm that Phobos has been inching closer to the red planet.

Even from Mars the moons don't look like moons. The more distant moon,

Deimos, appears more like a star in the night sky. While Phobos, which has the closest orbit to its primary of any moon in the solar system, still only appears a third as wide as Earth's full moon.

The image left is of Deimos and was captured by the Mars Reconnaissance Orbiter in 2009. CREDIT: NASA/JPL-caltech/University of Arizona - http://marsprogram.jpl.nasa.gov/mro/gallery/press/20090309a.html