Thick ice deposits in shallow simple craters on the Moon and Mercury

Abstract

Permanently shadowed regions near the poles of Mercury and the Moon may cold-trap water ice for geologic time periods. In past studies, thick ice deposits have been detected on Mercury, but not on the Moon, despite their similar thermal environments. Here we report evidence for thick ice deposits inside permanently shadowed simple craters on both Mercury and the Moon. We measure the depth/diameter ratio of approximately 2,000 simple craters near the north pole of Mercury using Mercury Laser Altimeter data. We find that these craters become distinctly shallower at higher latitudes, where ice is known to have accumulated on their floors. This shallowing corresponds to a maximum infill of around 50 m, consistent with previous estimates. A parallel investigation of approximately 12,000 lunar craters using Lunar Reconnaissance Orbiter data reveals a similar morphological trend near the south pole of the Moon, which we conclude is also due to the presence of thick ice deposits. We find that previously detected surface ice deposits in the south polar region of the Moon are spatially correlated with shallow craters, indicating that the surface ice may be exhumed or linked to the subsurface via diffusion. The family of lunar craters that we identify are promising targets for future missions, and may also help resolve the apparent discrepancy between the abundance of frozen volatiles on Mercury and the Moon.

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Fig. 1: Shallow craters near the poles of Mercury and the Moon.
Fig. 2: Sparse surface ice deposits previously identified on the Moon are negatively correlated with craters’ d/D.
Fig. 3: Ice accumulation, burial and gardening in an impact crater with a diameter of 3 km and d/D of 0.1.

Data availability

The crater catalogue and data that support the findings of this study are available through figshare with the identifier https://doi.org/10.6084/m9.figshare.7996304. The dataset may also be downloaded from https://figshare.com/s/90fb89d89f35786da658.

Code availability

The code used to model the temperature of permanently shadowed craters20 can be accessed through a GitHub repository with the identifier https://doi.org/10.5281/zenodo.3238628. It may also be downloaded from: https://github.com/liorruba/shallow_simple_craters.git.

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Acknowledgements

This work was supported in part by the Lunar Reconnaissance Orbiter Diviner (award no. NNG09EK06C) and MESSENGER (grant no. NNX07AR64G) missions. We are grateful to J.-P. Williams for helpful discussions and suggestions and S. Li for providing us with his previously published surface ice data. L.R. thanks T. Powell for many helpful discussions. The authors would also like to express their gratitude to the LOLA and MLA teams for acquiring high-precision laser altimeter datasets of the Moon and Mercury. LRO and MLA data were obtained from the Planetary Data System.

Author information

L.R. proposed the idea, and collected and analysed the majority of the data. J.V. assisted in identifying and measuring craters. L.R. interpreted the data and wrote the manuscript along with D.A.P.

Correspondence to Lior Rubanenko.

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