High charge-state solar wind ions interacting with comet 67P/Churyumov-Gerasimenko

Observations and comet activity estimates

¹ Swedish Institute of Space Physics, 981 92 Kiruna, Sweden
² Université d’Angers, 49000 Angers, France
³ Institute of Physics, University of Graz, Universitätspl. 5, 8010 Graz, Austria
⁴ Space Research & Planetary Sciences, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland

^★ Corresponding author: maxime.martin147@gmail.com

Received: 9 October 2025
Accepted: 30 October 2025

Abstract

Context. Solar wind interacts with the atmospheres of planets, moons, and comets. One of the important interaction processes is charge exchange. High charge-state heavy ions in solar wind are prone to charge exchange with typical atmospheric constituents due to their large cross-sections. These processes are important for remote observations of comets through X-ray emissions.

Aims. We survey the ESA/Rosetta data for in situ observations of multiply charged oxygen ions and estimate the neutral outgassing rate of comet 67P/Churyumov-Gerasimenko through the fluxes of heavy ions such as O⁶⁺ and O⁵⁺.

Methods. We used data from the Ion Composition Analyzer on board the Rosetta spacecraft to obtain oxygen ion fluxes. We found the expected signal to be weak and therefore applied careful data filtering. We then adapted a pre-existing model to calculate the outgassing rate of the comet.

Results. We find that multiply charged oxygen ions are mostly found post perihelion. The estimated outgassing rate is Q_O^th = 1.87 ⋅ 10²⁸ × R_h^−5.00 [s⁻¹], with R_h being the heliocentric distance.

Conclusions. Our outgassing estimates agree well with estimates from previous studies based on observations of helium ions. Our work extends these previous studies through the use of a completely independent dataset with coverage until the end of the Rosetta mission and by taking the varying neutral gas composition into account. The ratio of oxygen-to-helium fluxes we determined also matches previous measurements. Our comparison to ROSINA neutral gas measurements shows that heavy solar wind ions, such as oxygen, can be used to retrieve the neutral gas activity of the comet when direct neutral gas observations are not available.