Here we present a laboratory study demonstrating a low-temperature thermal oxidation reaction within H2O + H2S + O3 solid ice mixtures that produces observable sulfur anion products at temperatures as low as 90 K. This reaction primarily produces SO2, sulfur anions (including HSO 3 − , HSO 4 − , and SO 4 2 − ), and O2 at lower temperatures (90–140 K) and hydrated states of sulfuric acid (H2SO4: nH2O, where n = 0, 1, 4) at higher temperatures (150–250 K). We estimate that the overall activation energy to initiate these reactions is 20 ± 3 kJ mol−1, which is significantly lower than the activation energy required to oxidize SO2 to the sulfate ion. Given the detection of sulfur species on the surfaces of the Galilean satellites and the prevalence of radiolytically produced oxidants, we expect that these thermal reactions will play an important role in explaining the results obtained from future observations and missions that can measure the spatial distribution of these species.

Here we have investigated the degree to which energetic electrons cause structural changes in microporous H2O ice using infrared and ultraviolet–visible spectroscopy as analytical tools. In these studies, we found that energetic electrons destroy both the dangling bond (DB) absorption bands, indicative of internal surface area, and the internal porosity of our samples. In addition, we find it takes about a factor of 3 higher fluence to decrease the internal pore volume by 63.2% than it does the internal surface area, which is likely because the surface area decreases by both destruction of the internal pores and also by smaller pores coalescing into large ones. Extrapolating our results to the interstellar medium (ISM), we estimate that the time needed for these processes to occur is significantly shorter than the expected lifetime of a molecular cloud, leading us to speculate that future detections of the DB absorption bands or other indicators of porosity in the ISM will be relatively rare.

No abstract

No abstract

Transit spectroscopy is a key tool for exoplanet atmospheric characterization. However, transit spectrum observations can be limited by aerosol extinction when gas opacities are weak. The ultraviolet wavelength range contains a variety of strong molecular and atomic features, potentially enabling gas species detection even when atmospheric hazes are present. To understand the interplay between aerosol extinction and ultraviolet molecular opacities, we investigate transmission through the atmosphere of Saturn’s moon Titan during an occultation observed with the Ultraviolet Imaging Spectrometer (UVIS) on board NASA’s Cassini orbiter. We analyze the derived ultraviolet transit spectrum of Titan using exoplanet-relevant atmospheric retrieval models that both include and exclude treatments for hazes. Our retrieved gas column densities are consistent with previous studies analyzing UVIS occultation data. Despite the apparent haze impact on the underlying occultation data, our treatments fail to correctly characterize the haze in fits derived from simulated transit observations. This suggests that oversimplified haze parameterizations can hinder detection of atmospheric hazes in transit. Our work indicates that continued characterization of exoplanets in the ultraviolet wavelength regime can provide novel atmospheric constraints even if transit spectra are dominated by haze extinction at longer wavelengths.