1. Science Goals

Core science measurements are: high-resolution mapping of specific targets, surface change, geomorphology, topography, subsurface, thermal emission, SO₂, H₂O, D/H ratio, gravity, spin rate, and spin axis. The specific mission's goals are:^[1]

• Determine the level and nature of current activity.
• Determine the sequence of geological events that generated its range of surface features.
• Assess whether Venus once had oceans or was hospitable for life.
• Understand the organising geodynamic framework that controls the release of internal heat over the history of the planet.

The Lead Scientist is Richard Ghail, Royal Holloway, University of London. The two deputy lead scientists are Colin Wilson, Department of Physics, University of Oxford, UK (Science investigation lead) and Thomas Widemann, Observatoire de Paris/LESIA, France (Programme management lead).

2. Science Payload

The notional payload consists of three instruments and a Radio-Science Experiment:^[1][2]

• Venus Synthetic Aperture Radar (VenSAR) operates at 3.2 GHz in the S band (9.4 cm wavelength). VenSAR will provide several imaging and ranging techniques from a polar orbit: (1) regional and targeted surface mapping, (2) global topography and altimetry, (3) stereo imaging, (4) surface radiometry and scatterometry, (5) surface polarimetry, (6) repeat pass interferometry opportunities. The Jet Propulsion Laboratory’s S-band Synthetic Aperture Radar (VenSAR) selected by NASA is currently undergoing scientific, technical and mission assessment. A SAR is a versatile remote sensing technology that has unique capabilities for determining geophysical information often not available by other remote sensing methods. VenSAR will characterise structural, and geomorphic evidence of multi-scale processes that shaped the geological history of Venus as well as characterise current volcanic, tectonic, and sedimentary activity. The Principal Investigator of the Venus Synthetic Aperture Radar is Scott Hensley, Jet Propulsion Laboratory, NASA/California Institute of Technology.

• Venus Subsurface Radar Sounder (SRS) consists of a fixed dipole antenna operating in the range 9 - 30 MHz. SRS will search for subsurface material boundaries in various geological terrains that include impact craters and their infilling, buried craters, tesserae and their edges, plains, lava flows and their edges, and tectonic features in order to provide stratigraphic relationships at various depth ranges and horizontal scales. The Principal Investigator of the Subsurface Radar Sounder is Lorenzo Bruzzone, Università di Trento, Italy.^[2]

• Venus Spectroscopy suite (VenSpec) consists of three channels: VenSpec-M, VenSpec-H and VenSpec-U.
  VenSpec-M would provide compositional data on rock types; VenSpec-H would perform extremely high resolution atmospheric measurements; and VenSpec-U would monitor sulphured minor species (mainly SO and SO₂) as well as the mysterious UV absorber in Venusian upper clouds. This suite would search for temporal variations in surface temperatures and tropospheric concentrations of volcanic gases, indicative of volcanic eruptions. The Principal Investigator of the Venus Spectroscopy suite and PI of VenSpec-M is Jörn Helbert, DLR Institute of Planetary Research, Berlin, Germany. The PI of VenSpec-H is Ann Carine Vandaele, Royal Belgian Institute for Space Aeronomy (BIRA/IASB), Belgium. The PI of VenSpec-U is Emmanuel Marcq, LATMOS, IPSL, France.^[2]

3. Radio Science Experiment

Any orbiting spacecraft is sensitive to the local gravity field, plus the gravity field of the Sun and, to a minor extent, other planets. These gravitational perturbations generate spacecraft orbital velocity perturbations, from which the gravity field of a planet can be determined. EnVision's low-eccentricity, near-polar and relatively low altitude orbit^[2] offers the opportunity to obtain a high-resolution gravity field at each longitude and latitude of the Venusian globe. The analysis of the gravity field together with the topography gives insights on the lithospheric and crustal structure, allowing to better understand Venus's geological evolution. In the absence of seismic data, the measurements of the tidal deformation and proper motion of the planet provide the way to probe its deep internal structure (size and state of the core). The tidal deformation can be measured in the EnVision orbital velocity perturbations through the gravitational potential variations it generates (k2 tidal Love number).

The co-Principal Investigators of EnVision Radio Science and Gravity experiment are Caroline Dumoulin, LPG, Université de Nantes, France, and Pascal Rosenblatt, LPG, Université de Nantes, France.^[2]