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

Date: September 19, 2026 Source: Universe Today Summary: 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. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY The large impact crater known as Stickney is the largest crater on the Martian moon Phobos. 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. Credit: NASA/JPL-Caltech/University of Arizona 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 , 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. Stickney Crater Could Hold a Key Clue The enormous Stickney Crater is central to the debate over Phobos' history. If Phobos formed from debris created by a giant impact on Mars, the collision that produced the 9 km (5.6 mile) diameter crater may have occurred roughly 4.2 billion years ago. If Phobos was instead captured as an asteroid, the Stickney impact could have happened much later, around 2.6 billion years ago. Current estimates suggest that Phobos has a porous interior that may contain water ice, according to Benjamin Haser and co-author Thomas Andert in a 2026 paper published in The Monthly Notices of the Royal Astronomical Society (MNRAS). One promising way to investigate those possibilities is to map Phobos' gravity in greater detail. The researchers are particularly interested in whether the Stickney impact created a concentrated region of denser material beneath the crater. The Stickney event is one of the most important episodes in Phobos' history, and learning more about it could help scientists determine where the moon came from, Haser, a doctoral student in planetary science at Germany's Universität der Bundeswehr München, told me in Vienna.