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Peer-reviewedCC BY 4.0The Astrophysical Journal

Perpendicular Heating of Solar Wind Protons Driven by Proton Cyclotron Waves Upstream of Mars

  • Xiaotong Yun1,2,3
  • Song Fu1
  • Binbin Ni1
  • Hans Nilsson4
  • Gabriella Stenberg Wieser4
  • Shuyue Pang1
  • Taifeng Jin1
  • Longfei Jia1
  • Yi Qin1
  • Yibin Zhao1
  • Hengle Du1,2,3
4 affiliations
  1. 1Wuhan University
  2. 2China Research Institute of Radiowave Propagation
  3. 3National Key Laboratory of Electromagnetic Wave Propagation
  4. 4Swedish Institute of Space Physics
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Abstract

Proton cyclotron waves (PCWs) generated by newborn pickup ions are ubiquitous in the Martian upstream region, but their interaction with the solar wind remains poorly understood. Utilizing MAVEN observations, we report perpendicular heating of solar wind protons coincident with intense PCWs. During a 90 hr stream interaction region (SIR) passage, detailed observational and theoretical analyses of a representative event show that the measured large-amplitude ( B w / B ₀ up to ∼47%) quasi-parallel PCWs are intrinsically right-hand polarized and propagate sunward in the plasma frame, enabling Landau and multiple low-order anomalous Doppler cyclotron resonances with solar wind protons. Test particle simulations indicate a strong wave-induced pitch angle and energy diffusion of solar wind protons over moderate-to-large folded pitch angles, with diffusion coefficients reaching 10 ⁻⁴ –10 ⁻³ s ⁻¹ . Our findings highlight a fundamental wave-particle interaction process that can explain the observed perpendicular heating of solar wind protons upstream of Mars. In terms of a cross-population energy transfer from planetary pickup ions to the incident solar wind, Martian PCWs act as an important agent to actively reshape the upstream plasma environment and alter the solar wind thermodynamics.

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Cite

BibTeXRIS
BibTeX
@article{yun2026perpendicular,
  title = {{Perpendicular Heating of Solar Wind Protons Driven by Proton Cyclotron Waves Upstream of Mars}},
  author = {Xiaotong Yun and Song Fu and Binbin Ni and Hans Nilsson and Gabriella Stenberg Wieser and Shuyue Pang and Taifeng Jin and Longfei Jia and Yi Qin and Yibin Zhao and Hengle Du},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aeb018},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeb018},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Perpendicular Heating of Solar Wind Protons Driven by Proton Cyclotron Waves Upstream of Mars
AU  - Xiaotong Yun
AU  - Song Fu
AU  - Binbin Ni
AU  - Hans Nilsson
AU  - Gabriella Stenberg Wieser
AU  - Shuyue Pang
AU  - Taifeng Jin
AU  - Longfei Jia
AU  - Yi Qin
AU  - Yibin Zhao
AU  - Hengle Du
PY  - 2026
DA  - 2026/10/30
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aeb018
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aeb018
AB  - Proton cyclotron waves (PCWs) generated by newborn pickup ions are ubiquitous in the Martian upstream region, but their interaction with the solar wind remains poorly understood. Utilizing MAVEN observations, we report perpendicular heating of solar wind protons coincident with intense PCWs. During a 90 hr stream interaction region (SIR) passage, detailed observational and theoretical analyses of a representative event show that the measured large-amplitude ( B w / B ₀ up to ∼47%) quasi-parallel PCWs are intrinsically right-hand polarized and propagate sunward in the plasma frame, enabling Landau and multiple low-order anomalous Doppler cyclotron resonances with solar wind protons. Test particle simulations indicate a strong wave-induced pitch angle and energy diffusion of solar wind protons over moderate-to-large folded pitch angles, with diffusion coefficients reaching 10 ⁻⁴ –10 ⁻³ s ⁻¹ . Our findings highlight a fundamental wave-particle interaction process that can explain the observed perpendicular heating of solar wind protons upstream of Mars. In terms of a cross-population energy transfer from planetary pickup ions to the incident solar wind, Martian PCWs act as an important agent to actively reshape the upstream plasma environment and alter the solar wind thermodynamics.
SN  - 1538-4357
SN  - 0004-637X
ER  -