Strongly Subisothermal Polytropic Behavior of Ions in the Martian Magnetosheath Revealed by MAVEN Observations

Han-Wen Shen; Jasper S. Halekas; Shaosui Xu; Jih-Hong Shue; Yuanzheng Wen; Chi Zhang; Shannon M. Curry; David A. Brain; David L. Mitchell; Jared R. Espley

doi:10.3847/1538-4357/ae5a91

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Strongly Subisothermal Polytropic Behavior of Ions in the Martian Magnetosheath Revealed by MAVEN Observations

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Strongly Subisothermal Polytropic Behavior of Ions in the Martian Magnetosheath Revealed by MAVEN Observations

Han-Wen Shen, Jasper S. Halekas, Shaosui Xu, Jih-Hong Shue, Yuanzheng Wen, Chi Zhang, Shannon M. Curry, David A. Brain, David L. Mitchell and Jared R. Espley

The Astrophysical journal, Vol.1002(1), 108

05/01/2026

DOI: 10.3847/1538-4357/ae5a91

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Abstract

Energy redistribution during plasma compression or expansion remains poorly understood, particularly within induced magnetospheric systems. The polytropic index serves as an important diagnostic of this process by characterizing the thermodynamic response of temperature and pressure to density variations. This study presents the first statistical determination of the ion polytropic index in the Martian magnetosheath, leveraging 9 yr of Mars Atmosphere and Volatile EvolutioN (MAVEN) observations. Derived indices largely fall within the subisothermal range, yielding a median value of 0.42. Such polytropic behavior signifies systematic ion cooling during local compression-a thermodynamic response that departs significantly from both the adiabatic condition and the near-isothermal trends typically observed in Earth's magnetosheath. Beyond this characteristic, a well-defined spatial trend is also identified, with the index increasing radially from the bow shock toward the induced magnetosphere boundary. The polytropic index displays a clear anticorrelation with the amplitude of low-frequency magnetic field fluctuations, indicating a close association between wave activity and ion thermodynamics in the Martian magnetosheath. In summary, this study provides a pioneering quantitative characterization of ion polytropic behavior at Mars, offering a critical benchmark for comparative analyses between induced and intrinsic magnetospheric environments.

Physical Sciences

Astronomy & Astrophysics

Science & Technology

Details

Title: Subtitle: Strongly Subisothermal Polytropic Behavior of Ions in the Martian Magnetosheath Revealed by MAVEN Observations
Creators: Han-Wen Shen - Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA
Jasper S. Halekas - Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA
Shaosui Xu - Univ Calif Berkeley, Space Sci Lab, Berkeley, CA USA
Jih-Hong Shue - Natl Cent Univ, Dept Space Sci & Engn, Taoyuan, Taiwan
Yuanzheng Wen - Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA
Chi Zhang - Boston University
Shannon M. Curry - Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA
David A. Brain - Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA
David L. Mitchell - Univ Calif Berkeley, Space Sci Lab, Berkeley, CA USA
Jared R. Espley - NASA, Solar Syst Explorat Div, Goddard Space Flight Ctr, Greenbelt, MD USA
Resource Type: Journal article
Publication Details: The Astrophysical journal, Vol.1002(1), 108
DOI: 10.3847/1538-4357/ae5a91
ISSN: 0004-637X
eISSN: 1538-4357
Publisher: IOP Publishing Ltd
Number of pages: 9
Grant note: NNH10CC 04C / NASA divided by SMD divided by Planetary Science Division (PSD)
Language: English
Date published: 05/01/2026
Academic Unit: Physics and Astronomy
Record Identifier: 9985161339502771

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