Stickney crater on Mars’s moon Phobos

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Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

An image taken in 2008 by the Mars Reconnaissance Orbiter of the Stickney Crater, the largest crater on the martian moon Phobos.

The image was taken from a distance of 6000km. The Stickney crater is over 9km across, nearly half the diameter of the tiny moon itself.

Phobos is the largest of Mars’s two moons and orbits the planet at a distance of a mere 9400km going around the red planet every 7.5 hours or so, twice in every martian day.

Due to its small size and mass, Phobos remains an irregular shape as it is not massive enough to be rounded by its own gravity…. The gravity on Phobos is less than 1000th that on Earth.

Phobos is covered with a layer of fine dust (regolith) up to 100m metres deep which is believed to have originaled from extensive histoical impact cratering. The stripes around Stickney crater were originally thought to have resulted from the impact which formed the crater however it is now understood that these in fact originate from debris ejected into space resulting from impacts on Mars.

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Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

Phobos in its full glory. The moons’ origin is unclear and one school of thought is that it is actually a captured asteroid, originating from the asteriod belt between the orbits of Mars and Jupiter.

This gravitational attraction is continuing to draw Phobos ever closer to Mars and it is likely that within 10 million years or so, Phobos will be torn apart by the ever increasing gravitational tidal forces with its debris forming a new ring system around the red planet.

Phobos is named after the Greek god Phobos which means ‘fear’.