The Role of Mass Transfer between Martian satellites on Surface Geology

Abstract:

It has recently been recognized that impact ejecta can lead not only to prompt secondary craters, but projectiles that reimpact the target body or nearby companions after an extended period, producing so-called sesquinary craters [1]. Here we examine sesquinary cratering on the moons of Mars (cf. [2] for Phobos).

We model the impact that formed Voltaire, the largest crater on Deimos, and explore the orbital evolution of resulting ejecta across 500 years using four-body physics and particle following. The bulk of mass transfer to Phobos occurs in the first 100 years after impact, while reaccretions of ejecta to Deimos continue out to the 10⁴ year timescale as predicted by [3]. In the velocity range capable of reaching Phobos, 25-42% of ejecta mass reaccretes to Deimos and 12-21% impacts Phobos. Mass flux to Mars is <10%.

The time-averaged flux of Deimos material to Phobos can be as high as 11% of the background direct-to-Phobos impactor flux, a relatively minor contribution. However the ejecta mass reaccreted to Deimos from a Voltaire-sized impact is comparable to the expected direct-to-Deimos mass accumulated between Voltaire-size events. We find that the characteristic impact velocity of sesquinaries is an order of magnitude smaller than those of background (heliocentric) hypervelocity impactors and will likely result in different crater morphologies. A Voltaire-sized impact could feasibly resurface large parts of the moon, erasing the previous geological record. Dating the surface of Deimos may be more challenging than previously suspected. Deimos craters have been characterized as containing large amounts of fill due to sediment deposition [4]; our results suggest this fill to be sesquinary, as opposed to suborbital, in nature, which may also have implications for the smoothness of the Deimos surface.

[1] Zahnle et al., 2008, Icarus. [2] Chappaz et al., 2011, AAS. [3] Soter, 1971, Cornell. [4] Thomas and Veverka, 1980, Icarus.