A giant crater may reveal the origin of Mars’ doomed moon

Mars' innermost moon, Phobos, has puzzled planetary scientists for decades. One of the biggest unanswered questions is where it came from. Some researchers think Phobos is an asteroid that was captured by Mars, while others argue that it formed from debris thrown into orbit after a massive object slammed into the planet.

Solving that mystery may depend on something scientists still know surprisingly little about: what Phobos looks like on the inside.

Researchers are now trying to narrow down the possibilities by studying subtle characteristics of the moon, including its gravity and motion. At the recent European Geosciences Union general assembly in Vienna, scientists presented work modeling these geophysical measurements around one of Phobos' most dramatic features, Stickney Crater.