Electron-Induced Radiolysis of Water Ice and the Buildup of Oxygen

TL;DR

This study investigates how electron irradiation causes radiolysis in water ice, leading to the production and trapping of oxygen, with implications for icy bodies in the solar system.

Contribution

First laboratory measurements of electron-induced radiolysis in porous water ice, quantifying oxygen buildup and release dynamics in analog icy surfaces.

Findings

Oxygen can be trapped in irradiated ice under certain conditions.

Electron irradiation produces H2 and O2 as radiolysis products.

Oxygen residence times and saturation levels are quantified.

Abstract

Irradiation by energetic ions, electrons, and UV photons induces sputtering and chemical processes (radiolysis) in the surfaces of icy moons, comets, and icy grains. Laboratory experiments, both of ideal surfaces and of more complex and realistic analog samples, are crucial to understand the interaction of surfaces of icy moons and comets with their space environment. This study shows the first results of mass spectrometry measurements from porous water ice regolith samples irradiated with electrons as a representative analogy to water-ice rich surfaces in the solar system. Previous studies have shown that most electron-induced H2O radiolysis products leave the ice as H2 and O2 and that O2 can be trapped under certain conditions in the irradiated ice. Our new laboratory experiments confirm these findings. Moreover, they quantify residence times and saturation levels of O2 in originally pure water ice. H2O may also be released from the water ice by irradiation, but the quantification of the released H2O is more difficult and the total amount is sensitive to the electron flux and energy.