Daytime surface temperatures of the Moon derived from high-resolution IIRS on-board Chandrayaan-2

Abstract The Imaging Infra-Red Spectrometer (IIRS) on-board Chandrayaan-2 has been mapping the lunar surface since 2019 with high spatial (80 m/pixel) and spectral resolutions (20–25 nm). IIRS’s spectral range from 0.7 to 5 µm allows it to differentiate between the reflected as well as the thermal components. In this study, we have derived surface temperatures from sixteen IIRS strips, sourced from different parts of the lunar surface by inverting the Planck’s equation. Thereafter, for the first time, we have compared IIRS-derived temperatures with those retrieved from a lunar thermal model and Diviner. The results show that the temperature estimates from IIRS data are in good agreement with the thermal model and the Diviner data over a specific latitude range of ± 60° and time window of 09:30 − 14:00 hours local lunar time. The minimum and maximum mean absolute differences obtained for the temperature estimates by IIRS and the thermal model are 0.69 K and 23.9 K, respectively, for our suggested time and latitudinal range. These results demonstrate the robustness and reliability of the high-resolution IIRS-derived surface temperatures. Further, using the temperatures obtained from IIRS data, we investigated a part of the floor of the Schrödinger Basin comprising of a volcanic vent and found compositional diversity pointing towards the most recent and previously undetected episode of magmatic activity in the region. The findings were validated using Clementine-UVVIS multispectral data and crater chronology studies using Lunar Reconnaissance Orbiter – Narrow Angle Camera (LRO-NAC) data. This study, thus, highlights the importance of using high-resolution surface temperatures from IIRS to unravel such hitherto unknown aspects of lunar geology.