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Observations of interstellar helium pickup ions in the inner heliosphere

Gershman, Daniel J. and Gloeckler, George and Gilbert, Jason A. and Raines, Jim M. and Fisk, Lennard A. and Solomon, Sean C. and Stone, Edward C. and Zurbuchen, Thomas H. (2013) Observations of interstellar helium pickup ions in the inner heliosphere. Journal of Geophysical Research. Space Physics, 118 (4). pp. 1389-1402. ISSN 2169-9380.

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During the MESSENGER spacecraft's interplanetary trajectory to Mercury, the Fast Imaging Plasma Spectrometer (FIPS) measured the first helium pickup ion distributions at a heliocentric distance (R) ranging between 0.3 and 0.7 AU. From several transits of MESSENGER through the interstellar helium gravitational focusing cone, we map the cone structure in the ecliptic at R=0.3 AU and compare it with observations of He+ at R=1 AU made with the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE). Average downwind enhancements of ≈8 and average cone widths of ≈30° measured by each sensor match known models of neutral helium during this most recent, unusually quiet, solar minimum. The average cone center direction is calculated to be at J2000 ecliptic longitude λ_∞=76.0°(±6.0°) and 77.0°(±1.5°) from FIPS and SWICS observations, respectively. These parameters are also in agreement with previous determinations of the downwind direction of interstellar flow and demonstrate the effectiveness of using pickup ion observations inside 1 AU to map the structure of the neutral helium distribution in the heliosphere, as well as to diagnose the conditions of the interstellar medium.

Item Type:Article
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Stone, Edward C.0000-0002-2010-5462
Additional Information:© 2013 American Geophysical Union. Received 4 May 2012; revised 6 March 2013; accepted 10 March 2013; published 26 April 2013. The MESSENGER project is supported by the NASA Discovery Program under contracts NAS5-97271 to The Johns Hopkins University Applied Physics Laboratory and NASW-00002 to the Carnegie Institution of Washington. This work was also supported by the NASA Graduate Student Research Program grant NNX09AL50H (DJG), and the National Science Foundation grant AGS-1043012 (LAF).
Funding AgencyGrant Number
NASA Discovery ProgramNAS5-97271
NASA Discovery ProgramNASW-00002
NASA Graduate Student Research ProgramNNX09AL50H
Subject Keywords:pickup ion; interstellar helium
Issue or Number:4
Record Number:CaltechAUTHORS:20130715-115630155
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Official Citation:Gershman, D. J., G. Gloeckler, J. A. Gilbert, J. M. Raines, L. A. Fisk, S. C. Solomon, E. C. Stone, and T. H. Zurbuchen, (2013), Observations of interstellar helium pickup ions in the inner heliosphere, J. Geophys. Res. Space Physics, 118, 1389–1402, doi:10.1002/jgra.50227.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39364
Deposited By: Jason Perez
Deposited On:17 Jul 2013 16:29
Last Modified:20 Feb 2020 14:33

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