Isotopic ratio evolution in planetary materials by solar wind implantation
Qinting Jiang, Shun-ichiro Karato
Icarus
Available online 12 March 2026, 117046
“Highlights
- Heavier isotopes are enriched in solar wind-exposed materials.
- Penetration depth and exposure duration control the heavy isotope enrichment.
- Saturation level and solar wind history have slight influence.”
“Isotopic ratios provide important constraints on the origin of materials. When considering the volatile contribution from the Sun (i.e., the solar wind) to the terrestrial bodies, those volatiles trapped in the planetary materials are usually assumed to be the same as those of the Sun. However, this assumption requires careful evaluation: since the kinetic energy of solar wind particles is proportional to the particle mass, heavier elements/isotopes from the solar wind will penetrate deeper in those materials. Consequently, isotopic ratios of planetary materials exposed to the solar wind radiation will be different from the solar wind values. We propose a model showing the evolution of isotopic ratios of hydrogen and nitrogen in minerals (olivine and ilmenite) as a function of the exposure time to the solar wind. In this model, we also incorporate the evolution of the velocity (i.e., particle energy) and flux of the solar wind. Combining experimental results of hydrogen implantation on silicates and theoretical predictions by SRIM, we explore the effects of particle energy, particle and target species, saturation level, etc., on the isotopic ratio evolution of different minerals exposed to the solar wind. The modeling results are compared to observations of the materials from the surface of the planetary bodies such as lunar regolith, to help understand the contribution from the solar wind to their isotopic composition evolution.”
