Journal article
Structure and composition of the distant lunar exosphere: Constraints from ARTEMIS observations of ion acceleration in time‐varying fields
Journal of geophysical research. Planets, Vol.121(6), pp.1102-1115
06/2016
DOI: 10.1002/2016JE005082
PMCID: PMC7816729
PMID: 33479574
Abstract
By analyzing the trajectories of ionized constituents of the lunar exosphere in time‐varying electromagnetic fields, we can place constraints on the composition, structure, and dynamics of the lunar exosphere. Heavy ions travel slower than light ions in the same fields, so by observing the lag between field rotations and the response of ions from the lunar exosphere, we can place constraints on the composition of the ions. Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) provides an ideal platform to utilize such an analysis, since its two‐probe vantage allows precise timing of the propagation of field discontinuities in the solar wind, and its sensitive plasma instruments can detect the ion response. We demonstrate the utility of this technique by using fully time‐dependent charged particle tracing to analyze several minutes of ion observations taken by the two ARTEMIS probes ~3000–5000 km above the dusk terminator on 25 January 2014. The observations from this time period allow us to reach several interesting conclusions. The ion production at altitudes of a few hundred kilometers above the sunlit surface of the Moon has an unexpectedly significant contribution from species with masses of 40 amu or greater. The inferred distribution of the neutral source population has a large scale height, suggesting that micrometeorite impact vaporization and/or sputtering play an important role in the production of neutrals from the surface. Our observations also suggest an asymmetry in ion production, consistent with either a compositional variation in neutral vapor production or a local reduction in solar wind sputtering in magnetic regions of the surface.
Plain Language Summary
The ARTEMIS mission makes sensitive measurements of charged particles around the Moon, some of which come from the very tenuous lunar atmosphere. By timing how fast these charged particles move from their source to the spacecraft, we can determine what they are made of, and thereby better understand the composition and structure of the lunar atmosphere.
Key Points
Analyzing the time dependence of ion observations around the Moon allows us to place new constraints on the lunar exosphere
The high‐altitude lunar exosphere contains more heavy particles from sputtering and/or micrometeorite impact than expected
The lunar exosphere may be spatially inhomogeneous due to compositional variations and/or reductions in sputtering in magnetic regions
Details
- Title: Subtitle
- Structure and composition of the distant lunar exosphere: Constraints from ARTEMIS observations of ion acceleration in time‐varying fields
- Creators
- J. S Halekas - University of IowaA. R Poppe - University of California, BerkeleyW. M Farrell - Goddard Space Flight CenterJ. P McFadden - University of California, Berkeley
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Planets, Vol.121(6), pp.1102-1115
- DOI
- 10.1002/2016JE005082
- PMID
- 33479574
- PMCID
- PMC7816729
- ISSN
- 2169-9097
- eISSN
- 2169-9100
- Number of pages
- 14
- Grant note
- German Center for Aviation and Space (DLR) Solar System Exploration Research Virtual Institute NASA LASER (NNX13AJ97G) NASA (NAS5‐02099) German Ministry for Economy and Technology (50 OC 0302)
- Language
- English
- Date published
- 06/2016
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984199680802771
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