A giant crater on Mars may hold the key to understanding the origin of the planet’s doomed moon, Phobos, scientists say.

Phobos is slowly spiralling toward Mars and is expected to be torn apart by the planet’s gravity in tens of millions of years, eventually forming a ring around the red planet. How the small, lumpy moon formed in the first place has remained an open question.

The Crater Connection

Researchers have identified a large impact crater whose features may be linked to the moon’s birth. One leading idea is that a massive collision blasted debris into orbit around Mars, which later clumped together to form Phobos.

Studying the crater’s structure and composition could test whether this violent origin story holds up.

Why Phobos Is Doomed

Phobos orbits closer to Mars than any other moon orbits its planet, and tidal forces are dragging it inward by a small amount each year. In roughly 30 to 40 million years, it will cross the point where Mars’s gravity overwhelms its own cohesion.

When that happens, the moon will likely shatter into a ring of debris, a fate unique among the moons of the inner solar system.

What Comes Next

Upcoming missions to the Martian system could shed more light on the question. Japan’s MMX mission, for instance, is designed to visit Phobos and return samples to Earth.

Until then, the giant crater remains one of the most promising clues to how Mars acquired its ill-fated companion.

Phobos is only about 22 kilometres across, and its surface is scarred by craters, including the prominent Stickney crater that spans nearly half its width. Its low density suggests it may be a rubble pile rather than a solid rock, which would make it especially vulnerable once tidal stresses cross the critical threshold. Studying it up close remains a priority for planetary scientists.