Phobos May Shatter Earlier Than Expected in Violent Tidal Breakup

New research suggests Mars’s inner moon Phobos could break apart much sooner than the Roche limit due to its rubble-pile makeup and increasing tidal distortion. Initial surface shedding is predicted around 2.25 Mars radii, with larger fragmentation at about 2.15–2.13 RM, and instability near ~2.09 RM that could trigger breakup. Debris from these events may re-impinge on Phobos, accelerating destruction in a scenario called a sesquinary catastrophe. The MMX mission, launching in 2026, will study Phobos’s interior to refine these timelines.