Ion processing of ices and the origin of SO2 and O-3 on the icy surfaces of the icy jovian satellites

摘要

We present new experimental results relative to 144 keV S9+ or Ar9+ ion implantation in targets made of oxygen rich frozen gases (O-2, CO2) and mixtures with water ice. Spectra in the UV (200-400 nm) range have been obtained before and after implantation. The targets have been selected because they can be representative of the parent molecules from which SO2 and O-3, observed to be present on the surfaces of Jupiter's icy Moons, could be formed due to radiolysis induced by the abundant magnetospheric ions. The results indicate that sulfur dioxide is not detectable after sulfur implantation in oxygen bearing species. Ozone is formed after argon and sulfur ion implantation. Sulfur implantation in O-2 and CO2 targets also induces the formation of a band centered at about 255 nm (that we tentatively attribute to SO3- radicals). In the mixtures with water the band appears initially at the same wavelength and shifts to about 247 nm at higher ion fluences possibly indicating the formation of sulfite (HSO3-) ions. An absorption band observed on Ganymede is well fitted by using three components: ozone, sulfite ions and a not identified component having an absorption band centered at 298 nm. In all of the studied cases ion implantation produces a spectral reddening over the investigated spectral range (200-400 nm) that well mimics the observed spectral slopes of Jupiter's icy satellites. (C). 2016 Elsevier Inc. All rights reserved.