Regolith Mobility on Phobos: Dynamical Pathways, Surface Evolution, and Insights for MMX

Phobos exhibits some of the most enigmatic surface textures in the Solar System, from blue spectral units to smooth terrains and buried grooves. Understanding how regolith moves across its surface is essential for interpreting its geological history and for anticipating the environment that JAXA’s upcoming MMX mission will encounter.

In this seminar, I will present a new dynamical framework to investigate regolith mobility under Phobos’ extremely weak gravity, incorporating gravitational, tidal, and centrifugal, coriolis and self-gravity forces to map coherent dynamical regions (“Dynamical Features”) across the moon. By integrating particle motion with realistic friction laws, we introduce the concept of Regolith Migration Pathways preferred routes along which loose surface material naturally flows or creeps downslope.

Comparisons with high-resolution images and spectral data from MRO, MEX/HRSC reveal strong correlations between predicted pathways and observed smooth terrains, crater infilling, blue units, and areas of resurfacing. These results suggest that large-scale regolith motion has shaped both the sub-Mars and anti-Mars hemispheres, with implications for the origin of spectral heterogeneities and surface age estimates.

I will discuss how these findings inform the scientific context of MMX, particularly for sample-return operations near both the sub-Mars and anti-Mars points. The seminar will conclude with perspectives on future modelling improvements and how regolith dynamics may hold the key to deciphering Phobos’ internal structure, formation scenario, and long-term evolution.