This research addresses radiation effects on surface ices in outer solar system objects using laboratory techniques. Effects that alter the appearance of the ices are of special interest because they are significant for remote sensing of icy satellites, planetary rings and trans-Neptunian objects. Effects being explored include: a) the stability of molecules trapped in ice subject to ultraviolet solar radiation and magnetospheric ion impact; b) the relative efficiency of photons, electrons, light and heavy ions in affecting crystalline ice; and c) the electrostatic charging of surface ice by energetic particle impact. The research will use a unique combination of experimental techniques: exposure to ion, electron and laser beams and vacuum ultraviolet light, optical spectroscopy and interferometry, and microgravimetry and mass spectrometry at cryogenic temperatures in ultrahigh vacuum.
Broader impacts include inspiring students and educating them in the characteristics needed for quality research, professional development of early career scientists, and increased participation of under-represented groups. The work also brings techniques from surface science into laboratory astronomy.
The project involved experimental simulations of the interactions of the magnetospheres of Jupiter and Saturn with icy satellites. The work lead to the discovery of oxygen exosphere around Saturn's moon Rhea by the CASSINI spacecraft and the explanation of its origin. We performed the first experiments on electrostatic charging and discharging of ice by ion irradiation, which led to deeper understanding of the physics and provided a framework that is applicable from the interstellar space to the Earth's upper atmosphere. We discovered that ultraviolet light incident on porous ice in the presence of oxygen gas leads to the permanent uptake of gas, through the formation of hydrogen peroxide and ozone. This results shows that, in contrast with current ideas, radiation chemistry can occur deeper in ice than possible by charge particles in the magnetosphere. Finally, we measured the photodesorption of carbon dioxide to understand the stability of this molecule on the surface of icy satellites. The measurements show that the main gas desorbed is not CO2, as previously thought, but CO and oxygen. These results have implications on the abundance of molecules in interstellar space previous to solar system formation. The project allowed the successful completion of a PhD thesis. The project allowed the participation of an underrepresented minority (the principal investigator).
