Characterizing ponded craters on Vesta

Abstract:

The high-resolution images gathered by the framing camera of the Dawn mission [Sierks+ 2011] have identified many geological features on Vesta such as mass wasting process [Krohn+ 2014, Otto+ 2013] and large impact basins [Schenk+ 2012] that have been studied to assess the nature of Vesta’s regolith [Jaumann+ 2012]. Further the presence of pitted terrains [Denevi+ 2012], gully features on crater rims [Scully+ 2014] and formation of ponded crater under laboratory experiment [Sears+ 2015] revealed the possibility of volatile activity. So far ponded craters are identified on dry planetary bodies such as the Moon and asteroids Eros and Itokawa [Miyamoto+ 2007, Robinson+ 2001]. On different planetary bodies, the formation mechanism suggested for ponded craters varies depending upon its material properties and environmental conditions. Thus, we aim to understand the volatile involvement in the formation of ponded by exploring the detailed morphology of the ponded craters on Vesta.

Based on our investigation, we identified two types of ponded craters. Type 1 in which material appears as a smooth surface, equipotential distribution of fine grains covering the crater floor, a flat slope (≤15°) and shallow pond depth (~0.05-0.42 km). With close observation, we identified similar smooth surface material around craters. Based on the analysis of crater floor and the partially broken rim, we assume that the material distributed within crater to form pond characteristics and material surrounding the craters must have been from the similar source. However, not all the identified ponds follow similar morphology. In few examples, the ponded material is not distributed homogeneously within crater, defining type 2. The identified fine material is located at the foot of the crater wall or partially extending to the crater walls with increased slopes. These ponds are identified inside relatively large craters (5.90-10.05 km). Based on the topography, we depict that the loose fragmented material must have infilled the lowest regions of crater first and then built up the crater walls. In few examples, we inferred pit-like structures within ponded region but due to resolution restrictions it is difficult to imply if these are pits or secondary craters. In this talk we examine the evidence and its implications for Vesta’s regolith.