Phobos A Rubble Pile

Scientists using new data, including new images from Europe's Mars Express probe, have determined that Phobos, the larger moon of Mars, is in fact not one solid body, but several smaller pieces loosely held together by mutual gravitational attraction. Scientists literally call such objects "rubble piles."

One possible strategy for the manned exploration of Mars would establish a base on Phobos from which surface expeditions would depart and to which they would return. That strategy may be less viable now. The various pieces in the pile of Phobos no doubt occasionally shift around under changing gravitational influences. Likely, then, Phobos would not be seen as a stable platform for a base.

Of course, that still leaves the other tiny Martian moon, Deimos.