Surface mineralogy from the Venus Monitoring Camera observations: preliminary results from the re-processed images in 1 micron transparency “window”

Imaging of the Venus night side in the 1 µm spectral transparency “window” is a powerful tool to sound the surface mineralogy in the presence of thick clouds. Venus Monitoring Camera onboard Venus Express provided thousands of night side images covering low latitudes of the planet (30S – 30N). The first results of the geological analysis were published, for instance, by Basilevsky et al. (2012). Here we will present selected preliminary results of the geological analysis of the new data set derived in the framework of the ESA-MPS (Max Planck Institute for Solar System Research) contract (Shalygin and Shalygina, 2023).  

For the current analysis we selected several representative examples of geological units: shield plains, the lower unit of regional plains, lobate plains, and tesserae. The analysis suggests statistically significant spatial variations of the surface emissivity for the plains units likely indicating presence of non-basaltic components in the materials of lobate plains. The emissivity values of tesserae areas in Phoebe and Beta Regions show strong bimodality:  ~0.31±0.04 (3σ) for Phoebe Regio and ~0.50±0.18(3σ) for Beta Regio. If confirmed the bimodality would indicate significant compositional variations within a single morphological unit of tessera. Also, an anti-correlation between emissivity and elevation was found within specific units. This might suggest both emissivity changes with altitude as well as an artefact of not completely corrected atmospheric effects like temperature lapse rate and gas absorption coefficient, which role requires additional sensitivity studies.

References

A.T. Basilevsky, E.V. Shalygin, D.V. Titov et al. Geologic interpretation of the near-infrared images of the surface taken by the Venus Monitoring Camera, Venus Express. Icarus 217, pp 434-450, 2012.

E. Shalygin and O. Shalygina. Surface and cloud properties from VMC/Venus Express observations. Final Report (VMC-MPS-FR), ESA Contract 4000126833/18/NL/IB/gg, 2023.