Page last updated at 17:03 GMT, Thursday, 4 March 2010

Closest Phobos flyby gathers data

Phobos (Esa)
Phobos: When Mex took the image it was 656km from the Moon's centre

The European Mars Express (Mex) probe has made its closest flyby of the Martian moon Phobos, passing just 67km (42 miles) from its surface.

No manmade object has ever been so near to the natural satellite.

The approach is one of a series being made by Mex as it seeks to understand the origin of the moon.

Previous flybys have indicated that Phobos has an extremely low density, suggesting that its surface probably hides many large interior voids.

Scientists suspect the moon is simply a collection of planetary rubble that coalesced around the Red Planet sometime after its formation.

The Mex latest measurements will test this idea further. Very precise radio doppler data was gathered during the pass which will provide additional information on the moon's gravity field. Knowing the gravity field will help scientists to better understand the distribution of mass inside the moon.

Phobos is very slowly falling in towards Mars and tidal forces are expected to tear it apart one day.

The European Space Agency's Mars Express satellite has been in orbit since 25 December 2003.

It has made many discoveries including measurements of previously unrecognised methane in the planet's atmosphere.



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