Production of O2 on icy satellites by electronic excitation of low-temperature water ice

Abstract

The signature of condensed molecular oxygen has been reported in recent optical-reflectance measurements of the jovian moon Ganymede, and a tenuous oxygen atmosphere has been observed on Europa. The surfaces of these moons contain large amounts of water ice, and it is thought that O2 is formed by the sputtering of ice by energetic particles from the jovian magnetosphere. Understanding how O2 might be formed from low-temperature ice is crucial for theoretical and experimental simulations of the surfaces and atmospheres of icy bodies in the Solar System. Here we report laboratory measurements of the threshold energy, cross-section and temperature dependence of O2 production by electronic excitation of ice in vacuum, following electron-beam irradiation. Molecular oxygen is formed by direct excitation and dissociation of a stable precursor molecule, rather than (as has been previously thought) by diffusion and chemical recombination of precursor fragments. The large cross-section for O2 production suggests that electronic excitation plays an important part in the formation of O2 on Ganymede and Europa.

Photoelectric emission from the alkali metal doped vacuum-ice interface

“…Examples include formation of molecular oxygen and other products during high energy ͑Ͼ10 eV͒ photolysis, 1 hydrogen ion desorption and oxygen generation under electron bombardment, 2 electron and photon-induced chemistry of adsorbates on water-ice, 3,4 and the charging of nanosized ice particles in the mesosphere, leading to reduced mobility of the plasma around the particles and hence to the strong radar backscatter known as polar mesospheric summer echoes. 5,6 The structure, dynamics, and chemistry of electrons solvated in or at the surface of water-ice have attracted particular attention.…”

A Dynamic Landscape from Femtoseconds to Minutes for Excess Electrons at Ice−Metal Interfaces

“…Excess electrons in low-dimensional water and ice structures are of general importance in atmospheric science, chemistry, biology, and astrophysics [1][2][3][4][5] since electron-driven excitations and relaxation processes can induce reactions spanning a wide range of energy and time scales. 6 In bulk liquid water excess electrons are known to form a solvated complex in which the excess charge is screened 7 and decays by geminate recombination.…”

Europa Lander Mission: A Challenge to Find Traces of Alien Life

“…A wide range of possible ocean/crust compositions is the reason to construct different scenarios for the origin and evolution of putative ecosystems. The main energy sources, which could provide the support for the extant life at Europa are the tidal heating and the convection (Reynolds et al, 1983), radiolytic generation of oxidants (Chyba 2000;Sieger et al, 1998), chemoautotrophy (Kargel et al, 2000;Sieger et al, 1998), and possibly ionotrophy (Irwin and Schulze-Makuch, 2003). Microbial metabolites, dead biomass and also primordial organics must serve as a nutrient and energy sources for the attendant heterotrophic communities.…”

“…The analysis of Galileo mission data enables to develop new astrobiological concepts that speculate upon extant life on Europa (Reynolds et al, 1983;Sieger et al, 1998;Kargel et al, 2000;Chyba 2000). Several basic features of Europan evolution has been postulated by Kargel et al (2000): (1) initial carbonaceous chondrite rock; (2) global primordial low-temperature aqueous differentiation and formation of an impure primordial hydrous crust; (3) brine evolution and intracrustal differentiation; (4) degassing of Europa's mantle and gas venting; (5) hydrothermal processes, and (6) chemical alteration of the surface.…”