Late this month, ESA’s Mars Express will make the closest flyby yet of the Red Planet’s largest moon Phobos, skimming past at only 45 km above its surface.

The flyby on 29 December will be so close and fast that Mars Express will not be able to take any images, but instead it will yield the most accurate details yet of the moon’s gravitational field and, in turn, provide new details of its internal structure.

“At just 45 km from the surface, our spacecraft is passing almost within touching distance of Phobos,” says Michel Denis, Mars Express Operations Manager.

Full report via ESA web