Authors: Thomas P. C.
Title: Gravity, Tides, and Topography on Small Satellites and Asteroids: Application to Surface Features of the Martian Satellites
Abstract: The influence of gravitational potential on the disposition of loose material on the surfaces of small satellites is investigated using the martian satellites as examples. "Gravity" on small satellites can depend strongly on tidal and rotational effects, especially for objects of low mean density, such as Phobos. Numerical shape models of Phobos and Deimos allow the mapping of the relative gravitational positions of surface features. Dynamic height, derived from measures of potential energy, is a convenient approximation to heights above a reference equipotential surface for these irregular bodies. Deimos shows a strong correlation of indicators of global downslope movement with dynamic height. For Phobos, the distribution of dynamic heights across its surface has changed substantially over time due to its tidally evolving orbit that has induced changes in the rotational and tidal components of surface accelerations. Areas of minimum and maximum regolith thickness correlate better with high and low regions of dynamic height under conditions of rapid but synchronous rotation than with dynamic heights that occurred at more distant orbits less influenced by tides and rotation. However, some model-dependent measures of regolith depth, such as pit spacing in grooves, show little correlation with dynamic height at any orbit radius. The rougher surface of Phobos does not provide satellitewide pathways for near-surface downslope transport of material as does the surface of Deimos. Although the total amount of regolith on Phobos greatly exceeds that which can be attributed to the visible cratering record, the smoother surface of Deimos probably results from an even greater covering by debris from nearly catastrophic impacts. The Phobos and Deimos examples suggest that asteroids have global redistribution of ejecta only if debris from nearly catastrophic impacts provides smooth surfaces for long-distance downslope motion driven by small impact gardening, seismic effects of larger impacts, and thermal cycling.
Keywords: Deimos, Mars, Phobos, planetology
Journal: Icarus
Volume: 105
Number: 2
Pages: 326-344
Year: 1993
Bibliogaphic Code: 1993Icar..105..326T
Return to previous page