On Wednesday at 20:55 Central European Time the Mars Express spacecraft skirted by Phobos, the largest of Mars’s moons, at a distance of just 67 kilometres (press release).

The data isn’t back yet, that will happen tomorrow, and preliminary results will be out in a couple of weeks.

There’s a blog outlining the progress of the closest flyby, and there you can find out more about the breath-holding moments where the scientists on Earth crossed their fingers and hoped that Phobos didn’t get in the way at the crucial moment and block the singal between Earth and Mars Express. It didn’t, phew.

There’s also a video showing an animated version of what the flyby will have looked like.

The Mars Express satellite is a European Space Agency craft, and hs been up there since the end of 2003. The flyby of Phobos will get data that might help explain why the moon is so light – it seems to have an unusually low density and could just be a massive pile of rubble orbiting Mars. The flyby allowed Earthling scientists to detect tiny changes in radio waves transmitted from Mars Express to Earth – those changes will be related to the gravitational pull of Phobos and from that its mass can be calculated.

Image: ESA Flight Dynamics