Survival of Ancient Lunar Water Affected by Topographic Degradation of Old, Large Complex Craters
Lunar water is redistributed by various processes. Topographic diffusion affects the transport of water and contributes to its preservation in subsurface layers. Here, we analyze 16 complex craters (∼3.2 – ∼4.2 Ga) larger than 20 km in diameter near the lunar south pole to quantify their degradation...
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| Published in: | Geophysical research letters Vol. 49; no. 15 |
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| Main Authors: | , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Washington
John Wiley & Sons, Inc
16-08-2022
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Lunar water is redistributed by various processes. Topographic diffusion affects the transport of water and contributes to its preservation in subsurface layers. Here, we analyze 16 complex craters (∼3.2 – ∼4.2 Ga) larger than 20 km in diameter near the lunar south pole to quantify their degradation states. The results show that the diffusive rates of late Imbrian craters are similar to those of similarly aged simple craters, while Nectarian and pre‐Nectarian craters are degraded less efficiently. Within a complex crater, the mass accumulation by topographic diffusion and ejecta blankets from other complex craters preserves water, ranging up to 1 wt% on average. However, impact mixing and internal heat further limit the stability of ancient water to subsurface regions with ages younger than 3.9 Ga and at depth from a few meters to 10s of meters.
Plain Language Summary
Water in lunar shadowed regions is redistributed by various processes. When small craters form on a large crater's wall, its topography gradually erodes. Surface materials and deposited water move downhill, leading to a mixture of these materials and accumulations on the complex crater's floor. Here, we analyze 16 complex craters older than 3.2 Ga and larger than 20 km in diameter near the lunar south pole to investigate how fast these complex craters are topographically eroded. The results show that the speeds of topographic degradation of craters with an age of ∼3.2 Ga are comparable to those of similarly aged simple craters, while older craters experience significant degradation but are diffused inefficiently. On a complex crater, water may be stored in accumulated mass by topographic diffusion and large ejecta blankets for a long time. Such accumulated regions may host water, ranging up to 1 wt%. However, impact mixing and internal heat compete against the water supply and storage, limiting the water existence in subsurface layers at 10s of meters but a few meters below the surface and younger than 3.9 Ga.
Key Points
Topographic degradation of 16 complex craters near the lunar south pole significantly varies with surface age and crater size
Mass wasting by topographic diffusion and ejecta blanketing mixes water with regolith, giving a water mass fraction of up to 1 wt%
Impact mixing and internal heat limit the existence of unaffected ancient water at 10s of meters in depth and younger than 3.9 Ga |
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| ISSN: | 0094-8276 1944-8007 |
| DOI: | 10.1029/2022GL099241 |