Friday, June 03, 2016

Recent volcanic resurfacing of Venusian craters

Recent volcanic resurfacing of Venusian craters


Whitten et al


Ejecta from impact craters on Venus are a major source of fine-grained materials across the planet, and crater spatial distribution has been studied as a guide to the relative age and resurfacing rates of large regions. Of particular interest is the potential intersection of distal crater deposits and tesserae, highly deformed landforms that may be the oldest materials on Venus. The composition of tesserae is unknown, but is key to understanding whether water played a role in crustal differentiation. Thus, tesserae are ideal sites for future landed missions to identify possible felsic materials, but the short lifespan of surface landers means that efforts must be made to avoid contaminating surface materials from craters. Here we develop a method to detect distal crater ejecta on tessera terrain across Venus using NASA Magellan radar data. Our results show that fine-grained ejecta are unevenly distributed in the tesserae with respect to nearby craters. Many tesserae within a few hundred kilometers of plains craters do not have evidence for thick (greater than 5–10 cm) mantling material, indicating that eolian or mass-wasting processes have moved the debris off the highland ridge slopes. At Sudenitsa Tesserae, within the young Beta-Atla-Themis region, we observe a radar signature of mantling debris, but there is no apparent source crater to which this material can be traced. We infer that the source crater has been resurfaced by volcanic activity within the past 80 m.y., and suggest that similar fine-grained ejecta deposits may have built up over time in other tesserae across Venus.

No comments: