Nature 454, 67-70 (3 July 2008) | doi:10.1038/nature07030; Received 21 February 2008; Accepted 15 April 2008

Mediation of the solar wind termination shock by non-thermal ions

R. B. Decker1, S. M. Krimigis1,2, E. C. Roelof1, M. E. Hill1, T. P. Armstrong3, G. Gloeckler4, D. C. Hamilton5 & L. J. Lanzerotti6,7

  1. The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA
  2. Academy of Athens, Soranou Efesiou 4, Athens 11527, Greece
  3. Fundamental Technologies, 2411 Ponderosa, Suite A, Lawrence, Kansas 66046, USA
  4. University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109, USA
  5. University of Maryland, College Park, Maryland 20742, USA
  6. New Jersey Institute of Technology, Newark, New Jersey 07102, USA
  7. Alcatel-Lucent, Murray Hill, New Jersey 07974, USA

Correspondence to: R. B. Decker1 Correspondence and requests for materials should be addressed to R.B.D. (Email: robert.decker@jhuapl.edu).

Broad regions on both sides of the solar wind termination shock are populated by high intensities of non-thermal ions and electrons. The pre-shock particles in the solar wind have been measured by the spacecraft Voyager 1 (refs 1–5) and Voyager 2 (refs 3, 6). The post-shock particles in the heliosheath have also been measured by Voyager 1 (refs 3–5). It was not clear, however, what effect these particles might have on the physics of the shock transition until Voyager 2 crossed the shock on 31 August–1 September 2007 (refs 7–9). Unlike Voyager 1, Voyager 2 is making plasma measurements7. Data from the plasma7 and magnetic field8 instruments on Voyager 2 indicate that non-thermal ion distributions probably have key roles in mediating dynamical processes at the termination shock and in the heliosheath. Here we report that intensities of low-energy ions measured by Voyager 2 produce non-thermal partial ion pressures in the heliosheath that are comparable to (or exceed) both the thermal plasma pressures and the scalar magnetic field pressures. We conclude that these ions are the >0.028 MeV portion of the non-thermal ion distribution that determines the termination shock structure8 and the acceleration of which extracts a large fraction of bulk-flow kinetic energy from the incident solar wind7.


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