Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

¹ LERMA-LAMAp, UMR 8112 du CNRS, Observatoire de Paris et Université de Cergy-Pontoise, 5 mail Gay-Lussac, 95000 Cergy Pontoise Cedex, France ;
e-mail: econgiu@u-cergy.fr
² DMFCI, Università di Catania, Viale Doria 6, 95125 Catania, Italy

Abstract

Interstellar water ice is mainly amorphous, but the nature of its morphology still remains poorly known. The experimental study described in this work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. We show that there is an exponential decrease in the porosity of the amorphous water ice sample following hydrogen-atom irradiation. These and other laboratory results lead us to suggest that water ice in space is almost certainly amorphous and non-porous (compact).