Geologic interpretation of the NIR images taken by the Venus Monitorin Camera

Abstract

Joint analysis of the VMC 1 micron surface radiation images for the Beta-Phoebe region, the results of Magellan radar survey and the model images of this region showed that the VMC images provided reliable information on spatial variations of the NIR radiation of the Venus surface, which can be interpreted in terms of geological characteristics of the studied area,including potential compositional differences between geologic units. In particular, our analysis showed that surface of several relatively small massifs of tessera terrain observed in the study area showed the 1 micron emissivity which is not noticeably different from that typical of surrounding basaltic plains. This may mean that these tesserae are composed of basalts or it can be a result of pollution of surface of tessera by the wind-blown fine debris brought from the surrounding plains. This controversy hopefully may be resolved in future studies if much larger tessera massifs will be imaged by VMC. Analysis of the VMC images of the mountain tops covered with the enigmatic radar-low-emissivity material suggests that its 1 micron emissivity do not significantly differ from the emissivity of basalts that is consistent with earlier published geochemical conlusions that it can be hematite, or magnetite, or pyrite. We have found that the radar-bright and radar-dark subunits of the basaltic regional plains dominating in the study area do not show noticeable difference in their 1 micron emissivity. This was interpreted as indication on rather similar composition of these two plains varieties and differences in their radar brightness are probably due to differences in their surface roughness. We did not find any indication on ongoing volcanic eruptions in the study area that probably may be due to low spatial resolution of the VMC imaging and/or to actual absence of the ongoing volcanic activity. In our future studies we plan to involve to the analysis the new data acquired in the continuing Venus Express mission and to apply techniques of quantitative analysis to the existing and future data.