Mapping Venus in Emissivity: The Venus Emissivity Mapper, VenSpec-M on EnVision and VEM on VERITAS missions to Venus

Abstract

Understanding Venus’ surface composition and volcanic activity is central to addressing key questions about the planet’s evolution. These characteristics are tied to the degree of planetary differentiation Venus has undergone, as well as to post-formation geologic processes. Observations suggest Venus has been volcanically active in the past and is most likely active today. Venus Express revealed thermal anomalies and emissivity variations that suggested differences between fresh and weathered surface basaltic material, pointing to recently active hot spots[1,2,3,4]. Supporting this, gravity, topography, and deformation features observed at these locations are consistent with mantle plume activity beneath the surface[5,6]. Atmospheric sulfur dioxide (SO₂) fluctuations recorded by Pioneer Venus and Venus Express might reflect episodic volcanic outgassing[7,8,9] and accelerate surface alteration. Estimates of lithospheric thickness, used as a proxy for surface heat flow, suggest values comparable to Earth's most volcanically active regions[10]. Reanalysis of Magellan radar data has identified surface changes consistent with active eruptions[11,12]. However, key questions about surface composition and the intensity of recent magmatic processes on Venus remain unanswered. This will soon change, as three missions - NASA’s VERITAS and DAVINCI, and ESA’s EnVision - will investigate Venus with unprecedented detail. All three missions will include instruments targeting the 1 µm spectral windows, where the FeO absorption feature, a key indicator of mafic mineralogy, can be detected[13,14]. VERITAS and EnVision will carry Venus Emissivity Mappers (VEM on VERITAS, VenSpec-M on EnVision)[15,16], while DAVINCI will image the surface in this spectral range during flybys using VISOR and descent using VenDI[17].