^1,2,3G. Nishiyama,³T. Morota,^2,3,4N. Namiki,³K. Inoue,³S. Sugita
Journal of Geophysical Research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE008034]
¹Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany
²National Astronomical Observatory of Japan, Mitaka, Japan
³Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁴The Graduate University for Advanced Studies, SOKENDAI, Hayama, Japan
Published by arrangement with John Wiley & Sons

Linear gravity anomalies (LGAs) on the Moon have been interpreted as ancient magmatic intrusions formed during the lunar expansion. The composition of such ancient subsurface intrusions may offer hints for the lunar thermodynamic state in the initial stage of lunar history. To pose a first compositional constraint on magmatism related to lunar expansion, this study analyzed the spectrum and gravity around craters on LGAs, such as Rowland, Roche, and Edison craters. Using reflectance spectra around the craters, we first surveyed non-mare basaltic exposures. To test the LGA excavation scenario as a possible origin of the discovered exposures, we then compared the Gravity Recovery and Interior Laboratory data and post-cratering gravity simulation with the iSALE shock physics code. Our spectral analysis reveals no basaltic exposure around the Rowland crater. Further, the observed termination of LGA at the crater rim contradicts the gravity simulation, which assumes that LGA predates the Rowland crater. These results suggest that LGA formation might postdate the Rowland formation and that lunar expansion lasted even after the Nectarian age. On the other hand, we found that both Roche and Edison craters possess basaltic exposures in their peripheries. Because the gravity reduction inside Roche crater can be reproduced in our simulation, the discovered basaltic exposures are possibly LGA materials ejected from these craters. The composition of those exposures shows that the LGA intrusions at the two locations are composed of low-titanium magma, indicating that ancient magma during the expansion did not contain ilmenite-rich melt, perhaps resulting from the low-ilmenite content of the ancient upper mantle.

¹Arthur Goodwin, ²Christian Schröder, ²Emily Bonsall, ^1,3Russell J. Garwood, ¹Romain Tartèse
Earth and Planetary Science Letters 647, 119055 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.119055]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PY, UK
²Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK
³Natural History Museum, London, UK
Copyright Elsevier

The martian meteorite Northwest Africa (NWA) 11220 and paired stones (notably NWA 7034) are the only group of meteorites that sample a clastic near-surface lithology from Mars. The stones have been recognized as an impact-reworked lithology subjected to an impact-induced hydrothermal system — comparable to the postulated history of Jezero Crater, currently being explored by the NASA Perseverance rover. By applying Mössbauer spectroscopy in combination with several in situ analytical techniques including Raman spectroscopy, FTIR spectroscopy, and NanoSIMS, we show that aliphatic carbon compounds dominate the inventory of insoluble indigenous carbon compounds within NWA 11220. Disordered carbon — present in ∼5 μm heterogeneous masses — is preferentially found within porosity where it adjoins the mineral surface of titano-magnetite. This relationship suggests catalytic surfaces have enabled Fischer–Tropsch (FT) synthesis of hydrocarbons. Our in situ micron-scale analytical study indicates that such methods can help determine the origin of organic material that exists in the near-surface martian regolith. Such multimodal approaches will be a key methodology for searching for traces of past life in future samples returned from Mars.