Constraining surface composition and searching for volcanic activity on Venus: Preparing for future emissivity measurements by EnVision's VenSpec-M and VERITAS's VEM instruments

Some of the most outstanding questions about the evolution and present-day state of Venus involve the current level of volcanic activity and its 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 [e.g., 1,2,3,4,5].

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 needed. Three Venus missions (ESA’s EnVision and NASA’s VERITAS and DAVINCI missions) are scheduled to launch at the beginning of the next decade and explore our sister planet with unprecedented detail. All three missions include instruments targeting the 1 µm spectral region [6] where Fe transitions occur that may distinguish differences in surface composition [7]. Here we focus on the Venus Emissivity Mapper instrument, which is called VenSpec-M on EnVision mission and VEM on VERITAS mission, which will be used as a multi-spectral imaging systems [8, 9]. On EnVision, VenSpec-M is part of the VenSpec Suite, and together with high-resolution IR (VenSpec-H) and UV (VenSpec-U) spectrometers, it will provide critical information for understanding the surface-atmosphere interactions on Venus.

Both VenSpec-M and VEM instruments have six surface bands that cover five atmospheric windows around 1 µm. These will be used to distinguish between different rock types using relative (via slope and ratios between bands) and absolute (by comparison with laboratory experiments) emissivity. The instruments will also search for active volcanic eruptions on Venus using surface bands to search for thermal signatures associated with active volcanism, and three additional water vapor bands that are sensitive to the abundance of water vapor potentially associated with volcanic outgassing.

Currently, measurements are performed at PSL with the goal of building a comprehensive dataset for the interpretation of VEM data. These include measurements on basalts vs. granites samples; investigations of end-member mineral mixing effects in emissivity [10]; and studies of the emissivity response of weathered vs. unweathered Venus analogs [11]. Measurements on samples collected during field campaigns can be compared to field measurements performed using a VEM instrument emulator to improve data interpretation and calibration techniques [12]. The surface mapping performed by VenSpec-M on EnVision combined with VEM on VERITAS will characterize emissivity changes and provide nearly full coverage of Venus surface.

Acknowledgements: A portion of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract 80NM0020F0035 with NASA.

References:

[1] Helbert et al., GRL, 2008. [2] Smrekar et al., Science, 2010. [3] Smrekar et al., Nat. Geosci., 2023. [4] Herrick & Hensley, Science, 2023. [5] Sulcanese et al., Nat. Astron., 2024. [6] Helbert et al., Bulletin of the AAS, 2021. [7] Mueller et al., JGR, 2008. [8] Helbert et al. Proc. SPIE 10765, 2018. [9] Helbert et al., Proc. SPIE 11128, 2019. [10] Alemanno et al., LPSC, 2024. [11] Alemanno et al., LPSC, 2025. [12] Garland et al., LPSC, 2025.