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Implantation of sulfur ions into water-alkane ices: implications for the evolution of organic matter on Europa’s surface

Presentation #114.01 in the session Laboratory Investigations (Oral Presentation)

Published onOct 23, 2023
Implantation of sulfur ions into water-alkane ices: implications for the evolution of organic matter on Europa’s surface

We present the results of experiments of implantation of sulfur ions in ice samples (H2O:C3H8), in conditions relevant to Europa and other Jovian satellites. Europa experiences an intense bombardment of energetic particles [1]. This bombardment can heavily affect any organic matter from the ocean reaching the surface. Sulfur ions are abundant in Jupiter’s magnetosphere [1,2] due to Io’s volcanic activity, and highly reactive. Previous experiments with sulfur projectiles have shown the efficient creation of sulfuric acid in water ice [3, 4].

Here, in temperature conditions relevant to Europa (80 K), we investigate the composition of the organic residue generated by the irradiation of a water:propane ice with a 105 keV S7+ ion beam. Propane is the simplest alkane that can be condensed at a temperature relevant to Europa’s surface. The irradiated samples were slowly warmed up to 300 K to sublimate the volatiles and leave the refractory organic residue. This residue was analyzed using with Ultra-High Resolution Mass Spectrometry using two ionization techniques (laser desorption and electrospray). The analysis shows a very diverse (2500 + unique molecular formulas each) organic matter, with heavy molecules (m/z>200, up to 800) being common. We find large numbers of aromatic CH species and oxygen-rich, less aromatic species, depending on the ionization technique used. Organosulfurs are found both in CHS form and CHOS; they are fairly minor both in number and intensity.

These results demonstrate the possibility to form organosulfurs in the surface conditions of Europa starting from very simple organics. Due to the large quantities of sulfur implanted over time on the surface of Europa, the mass spectrometers onboard the JUICE and Europa Clipper missions should expect to detect multiple S-bearing organic species that originate in radiation driven chemistry on the surface.

[1] J.F. Cooper, et al.,. Icarus, 149(1), 133-159. (2001) [2] C. Paranicas et al.,., Europa. U. Arizona Press, Tucson, 529 (2009) [3] J.J.Ding,, et al.. Icarus, 226(1), 860-864. (2013) [4] Strazzulla, G., et al.. Icarus, 192(2), 623-628 (2007).

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