REVISITING MERCURY’S THERMOPHYSICAL PROPERTIES USING DATA FROM THE MARINER 10 INFRARED RADIOMETER

Until the arrival of BepiColombo (late 2025), the only infrared radiometer data of the surface of Mercury comes from the Mariner 10 spacecraft. The Mariner 10 Infrared Radiometer (IRR) collected a low latitude transect of ~11 and 45 micron radiance data across the night side of Mercury during its flyby in 1974. Those results were presented by [1] and provided an initial assessment of the thermophysical properties of the surface, including the identification of a low thermal inertia regolith, similar to the Earth’s Moon. Since the acquisition of the Mariner 10 IRR data, updated and more robust thermal models (i.e., detailed layering and temperature-dependent thermophysical properties) have been used to predict surface temperatures on Mercury.

Our work extends the analyses of previous studies in three ways: 1) an up-to-date thermal model is used to interpret the IRR measurements across a range of longitudes and local times. Most recent comparisons of thermal models to measurements have been limited, relying on telescopic microwave emission measurements, or focusing on model-based results in order to understand the thermal properties of polar regions. 2) With recent temperature and associated thermal modeling of the Moon, we can use the Moon as a framework to better understand and identify similarities and differences in their thermophysical properties. 3) Lastly, using imagery and compositional information from the MESSENGER spacecraft we are able to place these observations into geologic context. Our initial results indicate a strong similarity to typical lunar surfaces, characterized by extremely low thermal inertia values that are distinctly layered [2]. However, our results also suggest that there are wide swaths of the planet that likely have relatively uniform thermophysical properties. Although the Mariner 10 IRR data is limited in spatial scope, comparisons to more recent observations of the lunar surface may provide additional insight into the regolith and its formation on Mercury. Additionally, we hope that the results of this work can also serve as a template for future thermal infrared observations such as those from the Mercury Radiometer and Infrared Spectrometer (MERTIS) instrument onboard BepiColombo.

[1] Chase, S. C. et al. (1976), Icarus 28, 565

[2] Bandfield, J.L., M.M. Osterloo, G. M. Holsclaw (2019), 50^th Lunar. Planet. Sci. Conf. Abstract #2653