Phobos: Crater Clues May Decode a Martian Moon's Birth

Researchers at the EGU meeting modeled how small changes in Phobos’ geophysical signals around the 9‑km Stickney crater could help determine its interior and origin, weighing whether Phobos formed from debris after a giant Mars impact (~4.2 billion years ago) or was captured as an asteroid (~2.6 billion years ago). Current data suggest a porous interior with possible water ice and a localized denser mass near the equator, making gravity mapping and libration measurements key tests. The upcoming Japanese MMX mission (late 2026 launch) aims to orbit Phobos, collect surface samples with a core sampler and a NASA-provided pneumatic sampler, and return them to Earth by mid‑2031, which should help constrain Phobos’ formation scenario by linking interior structure, gravity, and composition.