NATURE OF LOCALIZED POND DEPOSITS ON ASTEROID VESTA

In our study, we proposed that downslope movement of impact melt and seismic shaking and/or volatile outgassing are responsible for the production of regolith ponds on the surface of Vesta. We observed 10 host crater candidates on Vesta which have overlapping characteristics of dust deposits of Eros, Itokawa [1,2] and melt deposits of the Moon [3]. Type 1 deposits have smooth pond surface, distributed at the low elevated part of craters and have relatively shallow depth with constant slope. In contrast, type 2 has a rough deposit surface with increasing slope within deposit terrain, pond material is partially off from the crater floor and often extended up to crater walls. However, both the types are observed within close vicinity of rarely large impact craters (such as Marcia, Cornelia).

Based on the flow-like surface features of the surrounding region, elevation heterogeneity and eroded topographic conditions of host craters, we hypothesis the downslope transportation of impact/ejecta melts from Marcia and Calpurnia to the topographic lows of the type 1 host craters. We name the smooth lens-like ponds as ejecta ponds. For type 2 pond deposits, we suspected either the low-amplitude seismic frequency and/or subsurface volatile outgassing as a potential carrier to transfer the dust-like granular media. Given the large size of Vesta, we indicate that the localized seismic shaking might be adequate to transport the material downslope. Additionally, Vesta has shown the presence of localized volatile induced surface activities (such as pits, gullies), thus we cannot rule out the subsurface volatile outgassing as a potential event to bring fine and coarse grains from beneath and resettle them on the surface. Nevertheless, both the occasions might be relatively short-lived which do not allow newly accumulated granular material to experience segregation and do not lead to attain smooth surface impression. Since type 2 deposits consist of loose fragmented dusty regolith particles, we name them as dust ponds.

References: [1] Fujiwara et al., 2006, Science. 312,1330; [2] Robinson et al., 2001, MPS. 37, 1651-1684; [3] Plescia and Cintala, 2012, JGR: Planets, 117