Micro cold traps on the Moon


Water ice is thought to be trapped in large permanently shadowed regions in the Moon’s polar regions, due to their extremely low temperatures. Here, we show that many unmapped cold traps exist on small spatial scales, substantially augmenting the areas where ice may accumulate. Using theoretical models and data from the Lunar Reconnaissance Orbiter, we estimate the contribution of shadows on scales from 1 km to 1 cm, the smallest distance over which we find cold-trapping to be effective for water ice. Approximately 10–20% of the permanent cold-trap area for water is found to be contained in these micro cold traps, which are the most numerous cold traps on the Moon. Consideration of all spatial scales therefore substantially increases the number of cold traps over previous estimates, for a total area of ~40,000 km2, about 60% of which is in the south. A majority of cold traps for water ice is found at latitudes > 80° because permanent shadows equatorward of 80° are typically too warm to support ice accumulation. Our results suggest that water trapped at the lunar poles may be more widely distributed and accessible as a resource for future missions than previously thought.

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Fig. 1: Images reveal shadows on a range of spatial scales.
Fig. 2: Modelled surface temperatures at 85° latitude for similar surfaces with two different values of σs.
Fig. 3: Fraction of total surface area at each latitude remaining perennially below 110 K, the adopted sublimation temperature for water ice.
Fig. 4: Permanently shadowed and cold-trapping areas as a function of size in the northern and southern hemispheres.

Data availability

All data used in this study are publicly available. The Diviner and LROC data can be accessed through the NASA Planetary Data System: https://pds-geosciences.wustl.edu. The higher-level data products generated in this study are available from the authors and on GitHub: https://github.com/phayne.

Code availability

All code generated by this study is available from the authors and/or on GitHub: https://github.com/phayne/heat1d and https://github.com/nschorgh/Planetary-Code-Collection/blob/master/Topo3D.


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This study was supported by the Lunar Reconnaissance Orbiter project and NASA’s Solar System Exploration Research Virtual Institute. We thank E. Mazarico for valuable discussions and data on PSR area derived from LOLA elevation data and illumination models, and P. Mahanti for crater depth/diameter ratio data. We also thank P. G. Lucey for insightful criticism that improved this work. O.A. wishes to thank the Helen Kimmel Center for Planetary Science, the Minerva Center for Life Under Extreme Planetary Conditions and the I-CORE Program of the PBC and ISF (centre no. 1829/12). N.S. was in part supported by the NASA Solar System Exploration Research Virtual Institute Cooperative Agreement (NNH16ZDA001N) (TREX).

Author information




P.O.H. initiated the study, developed the approach and general methodology, analysed the Diviner data and performed the model fitting. O.A. compiled the shadow fractions from images, computed the lateral heat conduction limitation and helped to construct the overall description of cold-trap scale dependence. N.S. derived the equations for shadows in a bowl-shaped crater and carried out the numerical energy balance calculations. All authors contributed to the writing of the manuscript.

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Correspondence to P. O. Hayne.

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Peer review information Nature Astronomy thanks Timothy McClanahan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Hayne, P.O., Aharonson, O. & Schörghofer, N. Micro cold traps on the Moon. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1198-9

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