ORIGINAL RESEARCH article
Front. Astron. Space Sci.
Sec. Stellar and Solar Physics
Volume 12 - 2025 | doi: 10.3389/fspas.2025.1586421
Collisional Thermalization of Minor Ions in the Solar Wind
Provisionally accepted
- University of Delaware, Newark, United States
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As the solar wind transits through the heliosphere, Coulomb collisions among constituent particles drives it toward local thermodynamic equilibrium. Prior studies of ion collisions in the solar wind have focused on the two most abundant solar wind ions: protons (ionized hydrogen) and α-particles (fully ionized helium). Some of the studies have used the technique of collisional analysis to incorporate the effects of collisions and expansion, to extrapolate the evolution of solar-wind ion temperature ratios. This study is the first to apply collisional analysis to the minor ions in the solar wind: carbon, oxygen and iron. Observations of ion temperature ratios in the near-Earth solar wind (r = 1.0 au) are used to predict their values closer to the Sun (r = 0.1 au). Ion measurements from the Advanced Composition Explorer (ACE) mission were used as individual boundary conditions for the equations of collisional analysis, which were solved numerically to make predictions of the temperature ratios. By using a large dataset spanning twelve years, the distributions of ion temperature ratios measured at r = 1.0 au can be compared to those predicted at r = 0.1 au.The predicted distributions suggest that the ratio of minor-ion temperatures to that of protons is significantly higher closer to the Sun, which is consistent with expectations for a zone of preferential minor-ion heating in/near the solar corona.
Keywords: Solar wind, heliosphere, Plasma, collision physics, Sun
Received: 02 Mar 2025; Accepted: 02 Jul 2025.
Copyright: © 2025 Johnson and Maruca. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Elliot Johnson, University of Delaware, Newark, United States
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