Gravity Modeling of Stickney Crater Tests Phobos Capture Versus Impact Origin

The study uses spacecraft-derived gravity and orbital data to simulate mass distribution inside the 22 km moon. Haser and Andert's 2026 MNRAS paper shows a porous interior possibly containing water ice, with potential denser material under the crater from impact compression. This anomaly would produce a detectable gravitational signal if the moon survived the strike due to low uniform density acting like a sponge. The approach connects the crater's thermal history directly to Phobos' bulk properties rather than relying solely on surface spectra.

Context from related work includes spectral analyses favoring asteroid capture and dynamical models of giant impacts on Mars that could loft debris into a disc. The new gravity focus fills a gap by probing interior structure, which neither spectral nor orbital decay data alone resolve. If a mass concentration is confirmed, it strengthens the impact-formation timeline; its absence would favor later capture. This integrates with Deimos studies showing similar but weaker features.

Next steps involve higher-resolution gravity mapping from proposed Phobos missions or landers. Refined models incorporating ice distribution and porosity gradients could be tested against future radio science data. Such measurements would also constrain tidal evolution rates and moon lifetime estimates.

The main evidence gap remains the absence of in-situ gravity measurements, limiting current simulations to indirect constraints from existing flybys.