Synergistic Observations of Venus’ Surface and Atmosphere: The Role of VenSpec on the ESA EnVision Mission

The ESA EnVision mission aims to provide a comprehensive understanding of Venus by investigating its geology and atmosphere, seeking to uncover why Venus and Earth, despite their similarities, have experienced such different evolutionary paths. 
A key payload on EnVision is the VenSpec Suite, designed to deliver unprecedented insights into Venus’ geological activity, atmospheric composition, and surface evolution. By targeting signatures of volcanic activity and mapping both surface and atmospheric features, VenSpec will seek to understand the processes shaping Venus today and in the past, and to provide insights into the evolution and habitability of terrestrial planets

The VenSpec Suite Instruments: The VenSpec Suite is following the holistic approach of the EnVision mission by studying the coupled system of surface and atmosphere on Venus with three complementary instruments, VenSpec-M, VenSpec-H, VenSpec-U and a Central Control Unit (CCU):

• VenSpec-U is an ultraviolet spectral imager (at low and high spectral resolution between 190 and 380 nm) [1]. By probing how volcanic outgassing and atmospheric dynamics interact through the upper cloud level, VenSpec-U complement and enhance the VenSpec-H and VenSpec-M observations.
• VenSpec-H is an infrared spectrometer, with four spectral bands in the near IR between 1.16 and 2.48 μm, that will provide measurements of atmospheric gases in the troposphere and mesosphere of Venus at high spectral resolution [2]. These observations will help identify volcanic plumes and gas exchanges with the surface, in coordination with VenSpec-M and VenSpec-U. Polarization filters are also included in the design to characterize the hazes in the mesosphere.
• VenSpec-M is a multispectral imaging spectrometer in 14 near-IR transparency windows (0.79–1.51 μm). It will observe the Venus surface across five atmospheric windows around 1 μm and monitor the planet for volcanic activity using clouds and water vapor bands [3]. To retrieve calibrated emissivity data from the Venus surface, VenSpec-M will utilize improved topography from NASA VERITAS’s VISAR and EnVision’s VenSAR-derived Digital Elevation Models (DEMs).
• The CCU is a simple and robust interface to the spacecraft, providing an abstraction layer between the channels and the spacecraft. The CCU offers a harmonized power and data interface to the spacecraft and allows the channels to design a simple, tailored internal interface to the CCU [4].

VenSpec Scientific Objectives: VenSpec will deliver crucial data for understanding Venus’ present state and evolutionary history, with the following primary objectives:

• Comprehensive Volcanic Activity Search - VenSpec will perform a thorough search for volcanic activity by detecting atmospheric, thermal, and compositional signatures, as well as by mapping surface composition globally;
• Atmosphere-Surface Coupling – The VenSpec suite is designed to follow volcanic plumes from their source near the surface (VenSpec-M, VenSpec-H) through the middle atmosphere (VenSpec-H) and up to the cloud tops (VenSpec-U), offering a holistic view of gas exchanges and atmospheric processes;
• Tropospheric trace gases - VenSpec-H will detect and quantify key volcanic and cloud-forming gases (SO₂, H₂O, HDO, OCS, CO, HCl) in the atmosphere, lower and upper;
• Surface Composition - VenSpec-M will provide near-global data on rock types and surface weathering, helping to understand crustal evolution and the history of volcanic resurfacing;
• Upper Atmosphere Studies - VenSpec-U and -H will monitor trace gases (CO, H₂O, OCS, SO, SO₂), cloud top altitude and the mysterious UV absorber in the upper clouds, shedding light on atmospheric chemistry and its links to volcanism

The VenSpec Joint Science Team: The VenSpec Suite is coordinated by a joint science team that ensures seamless integration and cooperation among the instruments. Rather than by channel, the science team is organized into interdisciplinary working groups that leverage synergies across all channels and foster collaboration among researchers and institutions. This structure enables more holistic investigations and promotes the sharing of data, models, and expertise.

Six cross-instrument Working Groups (WG) are currently actively engaged in preparatory science activities:

• Solar-Related Studies WG – focuses on a coordinated work to obtain good solar calibration and absolute measurements especially for VenSpec-U and VenSpec-H;
• Regions Of Interest WG – joints effort to produce a VenSpec targets list as input for the EnVision Regions Of Interest list based on scientific rationales and EnVision science requirements [5];
• Laboratory Investigations WG - supports the suite through laboratory experiments that simulate Venus’ surface and atmospheric conditions. The group fosters synergies between different laboratories and experimental approaches, providing essential reference data for instrument calibration and interpretation [6].
• Atmospheric Modelling WG – investigates models of Venus’ atmosphere, including cloud chemistry, sulfur processes (e.g., in-droplet S chemistry), and tropospheric and mesospheric SO₂ dynamics. Provide key chemical species vertical profiles to the Radiative Transfer WG.
• Radiative Transfer WG – focuses on radiative transfer codes intercomparison, i.e. methods, approximations and applications will be discussed.
• Ground-Based Observations WG - acts as a bridge between the Venus observation community and the radiative transfer modeling team. This group coordinates ground-based monitoring of atmospheric variability and dynamics, and advocates for Venus observations that complement space-based measurements [7].

These groups aim to address the most pressing questions about Venus’ surface and atmosphere through coordinated scientific strategies.

References: [1] Marcq et al. (2025, this meeting); [2] Robert et al. (2025, this meeting?); [3] Alemanno et al. (2025, this meeting); [4] Fitzner et al. (2024), SPIE Proc. 131440D. [5] Barraud et al. (2025a, this meeting); [6] Barraud et al. (2025b, this meeting); [7] Hueso et al. (2025, this meeting)