Phobos has gravity!

Last week Mars Express had its closest-ever flyby of Mars' larger, inner moon Phobos. They used the close encounter for radio science, to attempt to probe the inner structure of the little potato. It'll be a few weeks at least before they have any kind of reportable results on what that data tells them, but one thing that they can already report is that they have lovely data. Here's what it looks like:

The thick blue line shows you the effect Phobos would have had on Mars Express if its interior were homogeneous. Zoom in on the graph and you will see a thin gray squiggly line -- that's the actual spacecraft motion. Encoded in those squiggles is subtle information about the inhomogeneous distribution of mass within Phobos.

I don't know enough about radio science to read much into that gray squiggles. What I can say is that ESA has really stepped up their public information game, using their blog to disseminate frequent, fascinating stories about an active science mission. Thanks, ESA operations guys!