The Venus Surface Emissivity Mapper on the NASA's VERITAS and the VenSpec-M Instrument on ESA's EnVision Missions

Kurzfassung

Some of the most outstanding questions about the evolution and present-day state of Venus involve the current level of volcanic activity and surface composition, both directly linked to the amount of differentiation that our neighbor experienced through time. Several observations indicate that Venus was volcanically active in the recent past and that magmatic activity may still be ongoing. The presence of recently active hot-spots in the interior of Venus has been inferred based on 1.02 μm emissivity data of Venus Express, which may allow fresh and weathered basaltic material [1, 2, 3] to be distinguished, and on their thermal signatures [4]. In addition, gravity, topography and surface deformation structures at locations where recent volcanic activity has been suggested are consistent with the presence of mantle plumes in the interior [5, 6]. Furthermore, SO2 variations in the Venus atmosphere recorded by Pioneer Venus [7, 8] and later by Venus Express [9] provide additional evidence for recent volcanic activity [8, 9]. Elastic lithosphere thickness estimates for Venus, considered a proxy for surface heat flow, indicate heat flow values similar to active areas on Earth [10]. Recently, reanalysis of the Magellan synthetic aperture radar data indicates the presence of volcanic eruptions based on changes observed in radar images taken during different orbits [11, 12]. While there is growing evidence that Venus is a geologically active world, information about the surface composition and the level of magmatic activity is still lacking. Three Venus missions (NASA’s VERITAS and DAVINCI and ESA’s EnVision mission) are scheduled to launch at the beginning of the next decade and will explore our sister planet with unprecedented detail. All three missions include instruments targeting the 1 μm spectral region [13] where Fe transitions occur that may distinguish among different types of surface composition [14]. Both the VERITAS and EnVision missions will use the Venus Emissivity Mapper (called VEM on VERITAS and VenSpec-M on EnVision) instrument as a multi-spectral imaging system [15, 16], while the DAVINCI mission will use its Imaging System for Observational Reconnaissance (VISOR) [17] during flybys. The VEM instrument builds on the success of the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument on Venus Express and is designed for global mapping of the surface in all available spectral bands. On EnVision, VenSpec-M is part of the VenSpec Suite, and together with high-resolution IR (VenSpec-H) and UV (VenSpec-U) spectrometers will provide critical information for understanding the surface-atmosphere interactions on Venus.