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

A massive crater on Mars’ moon Phobos may hide a dense region of compressed material that could reveal whether the moon is a captured asteroid or debris from an ancient impact on Mars. Japan’s upcoming MMX sample return mission could provide the measurements and physical evidence needed to solve the mystery. A giant crater may reveal the origin of Mars’ doomed moon.

Some scientists believe the grooves and crater chains are related to the formation of Stickney, whereas others think they may have formed as a result of the ejecta from impacts on Mars that later collided with Phobos. The lineated textures on the walls of Stickney and other large craters are landslides formed from materials falling into the crater interiors. 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.