Hydrodynamic outflows of proto-lunar disk volatiles
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866914372034494464 |
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| author | Pahlevan, Kaveh Youdin, Andrew N. Sossi, Paolo A. |
| author_facet | Pahlevan, Kaveh Youdin, Andrew N. Sossi, Paolo A. |
| contents | Volatile elements - those that vaporize at low temperatures - are depleted in lunar rocks relative to terrestrial rocks. This systematic chemical depletion is evidence for vaporization and preferential removal of vapor from proto-lunar materials during the high-temperature processes accompanying lunar origin. Despite the robustness of these observations, the physical processes by which proto-lunar vapors were removed after the giant impact are not yet well-understood. Here, we show that toward the end of post-giant impact cooling history, Earth's atmosphere was dominated by carbon species (e.g., CO) and was spatially compact, behaving as a closed system retaining Earth's volatile inventory, whereas the proto-lunar disk atmosphere was dominated by H and H2 and was spatially extended, developing into a hydrodynamic outflow analogous to the solar wind. We find that equilibrium H2 recombination (2H->H2) in a partially-dissociated disk atmosphere produces a nearly isothermal structure, a feature known to activate outflows. The expected outflow was strong enough to propel proto-lunar volatiles from a Roche-interior (r < 3RE) disk out of Earth's gravity field and to establish a cometary tail composed of volatile elements transporting proto-lunar disk volatiles into interplanetary space. The proposed model suggests that the dichotomy in volatile element abundances between the silicate Earth and Moon is a natural outcome of the hydrodynamical behavior of magma ocean atmospheres and that lunar chemical and isotopic volatile abundances are diagnostic of the radial structure of the proto-lunar disk towards the end of its condensation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_05322 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Hydrodynamic outflows of proto-lunar disk volatiles Pahlevan, Kaveh Youdin, Andrew N. Sossi, Paolo A. Earth and Planetary Astrophysics Atmospheric and Oceanic Physics Geophysics Volatile elements - those that vaporize at low temperatures - are depleted in lunar rocks relative to terrestrial rocks. This systematic chemical depletion is evidence for vaporization and preferential removal of vapor from proto-lunar materials during the high-temperature processes accompanying lunar origin. Despite the robustness of these observations, the physical processes by which proto-lunar vapors were removed after the giant impact are not yet well-understood. Here, we show that toward the end of post-giant impact cooling history, Earth's atmosphere was dominated by carbon species (e.g., CO) and was spatially compact, behaving as a closed system retaining Earth's volatile inventory, whereas the proto-lunar disk atmosphere was dominated by H and H2 and was spatially extended, developing into a hydrodynamic outflow analogous to the solar wind. We find that equilibrium H2 recombination (2H->H2) in a partially-dissociated disk atmosphere produces a nearly isothermal structure, a feature known to activate outflows. The expected outflow was strong enough to propel proto-lunar volatiles from a Roche-interior (r < 3RE) disk out of Earth's gravity field and to establish a cometary tail composed of volatile elements transporting proto-lunar disk volatiles into interplanetary space. The proposed model suggests that the dichotomy in volatile element abundances between the silicate Earth and Moon is a natural outcome of the hydrodynamical behavior of magma ocean atmospheres and that lunar chemical and isotopic volatile abundances are diagnostic of the radial structure of the proto-lunar disk towards the end of its condensation. |
| title | Hydrodynamic outflows of proto-lunar disk volatiles |
| topic | Earth and Planetary Astrophysics Atmospheric and Oceanic Physics Geophysics |
| url | https://arxiv.org/abs/2603.05322 |