A Global Survey of Lunar Surface Thorium Anomalies Associated with Impact Basins
Radionuclides (e.g., thorium, uranium, and potassium) are the major sources of the Moon’s endogenic heat. While their surface occurrence can be mapped from orbit by gamma-ray spectrometry, knowledge of their subsurface distribution is crucial in further understanding the Moon’s thermal evolution. He...
Saved in:
| Main Author: | |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
|
| Series: | The Planetary Science Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/PSJ/ada49e |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1832576238247477248 |
|---|---|
| author | S. Nagihara |
| author_facet | S. Nagihara |
| author_sort | S. Nagihara |
| collection | DOAJ |
| description | Radionuclides (e.g., thorium, uranium, and potassium) are the major sources of the Moon’s endogenic heat. While their surface occurrence can be mapped from orbit by gamma-ray spectrometry, knowledge of their subsurface distribution is crucial in further understanding the Moon’s thermal evolution. Here we have conducted a global survey of surface Th anomalies (regionally elevated Th content) to locate Th-bearing materials and deduce their origin in the subsurface. We find that the Th-bearing surface materials originated in the crust–mantle transition zone and that they were brought to the surface by either excavation by major basin-forming impacts or mare volcanism, and in some cases nonmare volcanisms in the basin rim structures. The anorthosite crust contains near-zero Th as evidenced by the fresh ejecta from recent major impacts on the highlands such as Tycho. This holds true globally. Therefore, the lateral variation of surface Th content is controlled mainly by the distribution of the large (≳400 km diameter) mare basins of impact origin. This first-order variation can be altered significantly by two types of processes that take place after the basin formation. The one is the gradual dilution of the Th content of the surface materials over time by subsequent impact gardening. The other is reworking/redistribution/re-excavation of the basin ejecta from depth by later, large impacts. Because the lateral variation of surface Th content is controlled primarily by impact-related processes, it probably does not have positive correlation with that of endogenic heat flow. |
| format | Article |
| id | doaj-art-e5b29260e1694691a0a00df4e66ed206 |
| institution | Kabale University |
| issn | 2632-3338 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Planetary Science Journal |
| spelling | doaj-art-e5b29260e1694691a0a00df4e66ed2062025-01-31T08:40:56ZengIOP PublishingThe Planetary Science Journal2632-33382025-01-01623010.3847/PSJ/ada49eA Global Survey of Lunar Surface Thorium Anomalies Associated with Impact BasinsS. Nagihara0Department of Geosciences, Texas Tech University , Lubbock, TX 79423, USA ; seiichi.nagihara@ttu.eduRadionuclides (e.g., thorium, uranium, and potassium) are the major sources of the Moon’s endogenic heat. While their surface occurrence can be mapped from orbit by gamma-ray spectrometry, knowledge of their subsurface distribution is crucial in further understanding the Moon’s thermal evolution. Here we have conducted a global survey of surface Th anomalies (regionally elevated Th content) to locate Th-bearing materials and deduce their origin in the subsurface. We find that the Th-bearing surface materials originated in the crust–mantle transition zone and that they were brought to the surface by either excavation by major basin-forming impacts or mare volcanism, and in some cases nonmare volcanisms in the basin rim structures. The anorthosite crust contains near-zero Th as evidenced by the fresh ejecta from recent major impacts on the highlands such as Tycho. This holds true globally. Therefore, the lateral variation of surface Th content is controlled mainly by the distribution of the large (≳400 km diameter) mare basins of impact origin. This first-order variation can be altered significantly by two types of processes that take place after the basin formation. The one is the gradual dilution of the Th content of the surface materials over time by subsequent impact gardening. The other is reworking/redistribution/re-excavation of the basin ejecta from depth by later, large impacts. Because the lateral variation of surface Th content is controlled primarily by impact-related processes, it probably does not have positive correlation with that of endogenic heat flow.https://doi.org/10.3847/PSJ/ada49eThe MoonLunar composition |
| spellingShingle | S. Nagihara A Global Survey of Lunar Surface Thorium Anomalies Associated with Impact Basins The Planetary Science Journal The Moon Lunar composition |
| title | A Global Survey of Lunar Surface Thorium Anomalies Associated with Impact Basins |
| title_full | A Global Survey of Lunar Surface Thorium Anomalies Associated with Impact Basins |
| title_fullStr | A Global Survey of Lunar Surface Thorium Anomalies Associated with Impact Basins |
| title_full_unstemmed | A Global Survey of Lunar Surface Thorium Anomalies Associated with Impact Basins |
| title_short | A Global Survey of Lunar Surface Thorium Anomalies Associated with Impact Basins |
| title_sort | global survey of lunar surface thorium anomalies associated with impact basins |
| topic | The Moon Lunar composition |
| url | https://doi.org/10.3847/PSJ/ada49e |
| work_keys_str_mv | AT snagihara aglobalsurveyoflunarsurfacethoriumanomaliesassociatedwithimpactbasins AT snagihara globalsurveyoflunarsurfacethoriumanomaliesassociatedwithimpactbasins |