Energy Distribution of Pickup Ions at the Solar Wind Termination Shock

Rahul Kumar, Eric J. Zirnstein, Anatoly Spitkovsky

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


In-situ measurements taken by the Voyager 2 spacecraft suggest that the solar wind termination shock is significantly affected by the presence of pickup ions that are produced in the inner heliosphere due to charge exchange between interstellar neutrals and the solar wind ions. We use a fully kinetic particle-in-cell method to self-consistently simulate the shock with all physical properties available from Voyager 2. We have performed a set of simulations with varying velocity distribution functions for the pickup ions, since it was not determined by Voyager's measurements. We show that the measurements suggest that the pickup ions upstream of the shock are more energetic than generally believed. If their velocity distribution function assumes a filled-shell shape in the wind frame, the maximum cutoff speed for the pickup ions should be 650 km s-1 in order to reproduce the measurements, which is almost twice the local wind speed. We suggest that pickup ions upstream of the shock are energized by adiabatic compression of the solar wind plasma as well as due to an enhanced level of turbulence in a broad foreshock region.

Original languageEnglish (US)
Article number156
JournalAstrophysical Journal
Issue number2
StatePublished - Jun 20 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Sun: heliosphere
  • methods: numerical
  • plasmas
  • shock waves
  • solar wind


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