Radiation sputtering of organics on Europa’s icy surface

Jupitar’s icy moon Europa is continuously irradiated not only by solar photons also by energetic electrons, protons, and ions from the magnetospheric torus of Jupiter. Depending upon the energy, electrons can penetrate up to one meter on the icy surface of Europa, chemically alter the surface, and eject sputtered radiation products into the atmosphere. Investigating the radiation effects on the ice surface will be an important part to understand the exchange between Europa’s surface and its atmosphere. Upon irradiation, different types of materials may emit specific sputtered products. Any unique sputtering products can be used to link the local surface composition with Europa’s atmosphere. To mimic Europa’s conditions at JPL’s Ice Spectroscopy Lab (ISL), we used ultrahigh vacuum systems and cryocooling. We studied the radiation sputtering at 100 K which is the average surface temperature of Europa’s icy surface. We vapor deposited organic molecules with different functional groups (e.g., hexane and hexanoic acid) and water onto a cold substrate and exposed them to energetic electrons with a 2 keV electron gun as the radiation source. Different organic byproducts are detected by a quadrupole mass spectrometer. Although it is unknown what carbon-containing compounds could exist on the surface of Europa, these experiments will provide an important reference point for evolved gas signature detection, to determine the types of molecules that can be produced with and without a surrounding ice water matrix. The data from this work on the radiation effects at Europa’s surface could help improve our understanding of exchange between Europa’s surface and its atmosphere.