Radiation Chemical Weathering of Water-Rich Surfaces

Water ice is known to exist on nineteen different moons of the four giant planets, and also on Pluto's moon, the rings of Saturn, trans-Neptunian objects, and comets. Other condensed volatiles have also been detected on many of these objects. These solar system ices exist in a variety of radiation environments that can include magnetospheric ions and cosmic rays. To study the radiation chemical weathering of water-rich ices, we record changes in the mid-IR spectra of low-temperature thin ice films during ion bombardment. We have completed a variety of MeV proton irradiation experiments on both pure H₂O and H₂O-dominated ices containing CO₂, CO, CH₄, and NH₃. This talk will focus on the radiation chemical processes that lead to the formation of H₂O₂ (a detected radiation product on Europa, (Carlson et al. 1999)) and carbonic acid, H₂CO₃ (a candidate whose IR spectrum is similar to observed features on Callisto, (Carlson, 2001)). We will identify other radiation products that are most likely to be observed from mixtures such as H₂O + CH₄, H₂O + CO, H₂O + NH₃. The role of CO₂ in the formation of O₂ will also be discussed. This research is funded through NRA 344-33-01 and 344-02-57 Carlson et al. (1999) Science, 283, 2062 Carlson (2001) private communication