Journal article
LRO/LAMP observations of the lunar helium exosphere: constraints on thermal accommodation and outgassing rate
Monthly notices of the Royal Astronomical Society, Vol.501(3), pp.4438-4451
03/01/2021
DOI: 10.1093/mnras/staa3884
Abstract
We report a comprehensive study by the UV spectrograph LAMP (Lyman-Alpha Mapping Project) onboard the Lunar Reconnaissance Orbiter to map the spatial distribution and temporal evolution of helium atoms in the lunar exosphere, via spectroscopy of the He I emission line at 58.4 nm. Comparisons with several Monte Carlo models show that lunar exospheric helium is fully thermalized with the surface (accommodation coefficient of 1.0). LAMP-derived helium source rates are compared to the flux of solar wind alpha particles measured in situ by the ARTEMIS twin spacecraft. Our observations confirm that these alpha particles (He++) are the main source of lunar exospheric helium, representing 79 per cent of the total source rate, with the remaining 21 per cent presumed to be outgassing from the lunar interior. The endogenic source rate we derive, (1.49 +/- 0.08) x 10(6) cm(-2) s(-1), is consistent with previous measurements but is now better constrained. LAMP-constrained exospheric surface densities present a dawn/dusk ratio of similar to 1.8, within the value measured by the Apollo 17 surface mass spectrometer LACE (Lunar Atmosphere Composition Experiment). Finally, observations of lunar helium during three Earth's magnetotail crossings, when the Moon is shielded from the solar wind, confirm previous observations of an exponential decay of helium with a time constant of 4.5 d
Details
- Title: Subtitle
- LRO/LAMP observations of the lunar helium exosphere: constraints on thermal accommodation and outgassing rate
- Creators
- Cesare Grava - Southwest Research InstituteDana M. Hurley - Johns Hopkins University Applied Physics LaboratoryPaul D. Feldman - Johns Hopkins UniversityKurt D. Retherford - Southwest Research InstituteThomas K. Greathouse - Southwest Research InstituteWayne R. Pryor - Central Arizona CollegeG. Randall Gladstone - Southwest Research InstituteJasper S. Halekas - University of IowaKathleen E. Mandt - Johns Hopkins University Applied Physics LaboratoryDanielle Y. Wyrick - Southwest Research InstituteMichael W. Davis - Southwest Research InstituteAnthony F. Egan - Southwest Research InstituteDavid E. Kaufmann - Southwest Research InstituteMaarten H. Versteeg - Southwest Research InstituteS. Alan Stern - Southwest Research Institute
- Resource Type
- Journal article
- Publication Details
- Monthly notices of the Royal Astronomical Society, Vol.501(3), pp.4438-4451
- Publisher
- Oxford Univ Press
- DOI
- 10.1093/mnras/staa3884
- ISSN
- 0035-8711
- eISSN
- 1365-2966
- Number of pages
- 14
- Grant note
- NNG05EC87C / National Aeronautics and Space Administration (NASA); National Aeronautics & Space Administration (NASA)
- Language
- English
- Date published
- 03/01/2021
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984428822202771
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