The deepest secrets of Mars鈥檚 moon Phobos are set to be revealed, following a series of 12 fly-bys by Europe鈥檚 Mars Express spacecraft. Six have been completed, including the closest ever pass of the moon, at 67 km, last week.
The flights will probe the moon鈥檚 gravity better than ever before, revealing the distribution of material throughout its body. The MARSIS radar will also search for underground structures in the rubbly moon, which is probably riddled with caverns.
The gravity data will help Russia鈥檚 Phobos-Grunt mission, set to launch in 2011 or 2012, manoeuvre efficiently around the moon before coming in for a landing.
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New portraits of Phobos are also on the way. 鈥淯ntil now, the encounters have been on the [moon鈥檚] nightside,鈥� says ESA鈥檚 project scientist Olivier Witasse. 鈥淭his week we switch to flying by the daylight side, allowing the camera and spectrometers to begin working.鈥� That will give the moon鈥檚 composition, testing the idea that Phobos formed from rocks that somehow found themselves orbiting the planet.
Unfortunately, a 90-metre-high rocky outcrop called the 鈥榤onolith鈥� is not visible to Mars Express during this series of fly-bys. The monolith could be a piece of Phobos鈥檚 interior thrown to the surface during the formation of a crater. It was first spotted in 1999, on images taken by NASA鈥檚 Mars Global Surveyor probe.
