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

Scientists modeled Phobos's gravitational field around the 9 km Stickney crater to determine whether the moon was a captured asteroid or formed from debris of an impact on Mars. Estimates point to a porous core with possible water ice; Japan's MMX mission is to launch in late 2026 and return samples.

• Stickney crater diameter is 9 km, Phobos mean diameter is 22.2 km
• If Phobos is impact debris from Mars, crater formed ~4.2 billion years ago; if captured asteroid, ~2.6 billion years ago
• Phobos orbits Mars in 7 hours 39 minutes and is gradually approaching the planet
• MMX mission aims to launch in late 2026 with return of Phobos samples