The Great Hellas Impactor: A Catastrophic Angular Momentum Transfer Model for Martian Dynamo Cessation and Atmospheric Loss

Abstract Mars once possessed flowing water, a thick atmosphere, and a protective magnetic field. Today it is a cold, desiccated husk. The conventional explanation attributes this transformation to thermal processes—a small planet cooling too quickly to sustain its dynamo. This paper proposes an alternative: the Hellas impact, one of the largest collisions in solar system history, mechanically killed Mars’ magnetic dynamo through catastrophic angular momentum transfer.The hypothesis unifies four previously isolated observations: the Hellas Basin itself, the antipodal Tharsis volcanic province with its 1,100 km magma plume recently mapped by gravity surveys, the ancient mantle debris detected by NASA’s InSight seismometer, and the solid inner core confirmed in 2025. Together, these point to a single cataclysmic event that disrupted organized convection in Mars’ liquid core—terminating the electromagnetic shield that protected its atmosphere from solar wind stripping.Saturn’s moon Titan, smaller than Mars yet possessing an atmosphere denser than Earth’s under Saturn’s magnetospheric protection, demonstrates that planetary size is not the determining factor. Electromagnetic shielding is. Mars lost that shield not through gradual cooling, but through cosmic accident.The mechanical cessation hypothesis generates a specific, falsifiable prediction: paleomagnetic analysis of returned Martian samples should reveal abrupt rather than gradual field collapse—a step function, not a declining ramp. Mars Sample Return missions to Jezero crater could provide the definitive test.