Suprathermal H+ Pickup Ion Tails in the Outer Heliosphere

Bishwas L. Shrestha, Eric J. Zirnstein, David J. McComas, Pontus Brandt, Alan Stern, Heather A. Elliott, Andrew R. Poppe, Kelsi N. Singer, Anne Verbiscer

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


This study provides a detailed analysis of five distant interplanetary shocks observed by the Solar Wind Around Pluto instrument on board New Horizons, which exhibit the signature of a suprathermal H+ pickup ion (PUI) tail in the downstream distribution. These shocks were observed with a PUI data cadence of approximately 24 hr, covering a heliocentric distance range of 23.71–36.75 au. The shock compression ratio varies between approximately 1.4 and 3.2. The H+ PUI density and temperature show a gradual increase across the shock, while the H+ solar wind density shows erratic behavior without a distinct downstream compression. The H+ PUI cooling index variation across the shock displays different characteristics in each shock. This study demonstrates, for the first time, the variation of the number density of downstream H+ PUI tails with the shock compression ratio, revealing an increase in tail density with stronger shocks. Additionally, theoretical estimates of reflected PUI number densities derived from the electrostatic cross-shock potential agree very well with the observed H+ PUI tail densities for stronger shocks.

Original languageEnglish (US)
Article number35
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 1 2024

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Heliosphere (711)
  • Interplanetary particle acceleration (826)
  • Interplanetary shocks (829)
  • Pickup ions (1239)
  • Plasma physics (2089)
  • Solar wind (1534)
  • Space plasmas (1544)


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