Moon Caves

19.07.2024

The study Radar Evidence of an Accessible Cave Conduit below the Mare Tranquillitatis Pit published in Nature Astronomy analyses radar images of the Mare Tranquillitatis pit (MTP), an elliptical skylight with vertical or overhanging walls and a sloping pit floor that seems to extend further underground. The images were obtained by the Mini-RF instrument onboard the Lunar Reconnaissance Orbiter in 2010. Although the main study was carried out by the University of Trento, Riccardo Pozzobon of the University of Padua specifically validated the data obtained from the MiniRF radar to ensure a credible geological interpretation. 

The presence of lunar caves has been theorized and discussed for over 50 years and now their existence has been demonstrated with the publication of the article.

Researchers observed an empty cave conduit, interpreted as a potential lava tube that provides a means of deep access to the lunar subsurface through a collapse known as Mare Tranquillitatis Pit, which is located within the basaltic basin of the same name. Direct observation was made possible using an innovative radar image processing technique developed by the University of Trento researchers that can see through darkness. This method was applied to radar data collected by the Mini-RF radar sensor currently orbiting the Moon. 

Riccardo Pozzobon, a researcher in planetary geology at the Department of Geosciences of the University of Padua, and an expert in satellite remote sensing of planetary surfaces and terrestrial analogues, provided geological expertise for these volcanic structures. He specifically validated the data obtained from the MiniRF radar to ensure a credible geological interpretation.

Pozzobon explains: “To do this, we used the surface of the Moon and the visible Mare Tranquillitatis pit as a reference, which had been reconstructed using stereophotogrammetry from satellite images from LROC. Through this process, we create a 3D simulation of the geometry of the cave, including the vertical pit and a potential extension below the surface. Multiple models were created, and using a ray tracing simulator, we modified the geometry of the model. This allowed us to simulate the radar beam, which would penetrate the surface through an aperture and then bounce back. By doing so, we matched the output of the radar simulations with the real observed data taken on the surface of the Moon.”

3D simulation model: 3D model used in the validation tests of the radar observations of the Mare Tranquillitatis Pit. In orange the real lunar topography reconstructed from stereo-photogrammetric satellite data, and in blue the simulated data that correspond to what was observed by the MiniRF radar. The collapse with vertical walls, the pile of debris at the bottom populated with large boulders and the extension of the detected cavity are visible. The point of view is from bottom to top. The width of the conduit is as wide as or more than the dimensions of the Mare Tranquillitatis Pit collapse. Topography is obtained from LROC NAC data from Wagner, R. v., & Robinson, M. S. (2022) Lunar Pit Morphology: Implications for Exploration. Journal of Geophysical Research: Planets, 127(8).
Lunar pit: The lunar Mare Tranquillitatis Pit hides an accessible cavity ten of meters long in the subsurface of the Moon. The cavity was identified by analyzing radar images obtained by the Mini-RF radar on board the Lunar Reconnaissance Orbiter. Credits: photo by A. Romeo.