[P-PS01] Outer Solar System Exploration Today, and Tomorrow

[PPS01-P04] Elemental sources for Europa's surface materials unveiled by oxygen ion irradiation to sulfates

*Misako Otsuki¹, Tomoki Kimura¹, Tomohiro Kitano¹, Ryo Hoshino¹, Yusuke Nakauchi², Fuminori Tsuchiya³ (1.Tokyo University of Science, 2.Japan Aerospace Exploration Agency, 3.Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University)

Keywords:Europa, radiation chemistry, surface composition

Jupiter's icy moon Europa likely has an interior water ocean within the icy shell. To elucidate the chemical composition of the interior ocean is the most important problem to be solved for assessing the habitability there. Sulfur is one of the possible constituent elements of surface materials on Europa. Endogenic and exogenic sources have been proposed for the sulfur in the surface material. In the former case, the sulfur is provided as the sulfates plumed from the interior ocean [Kargel et al., 2000], and in the latter case it is provided as the sulfur dioxide(SO₂) supplied from the volcanoes at the moon Io [Alvarellos et al., 2008]. The surface materials are suggested to be chemically altered continuously by irradiation of Iogenic high-energy sulfur and oxygen ions to the surface, which drive the radiation chemical cycles between the sulfur and other compounds [Carlson et al., 2002], which mimics the source of surface sulfur. This study unveils the source of sulfur on Europa's surface by modeling the radiation chemical cycle based on the laboratory experiment of oxygen ion irradiation to the magnesium sulfate(MgSO₄) sample, which is a possible candidate for the surface material of Europa. We found that sulfur allotropes such as octasulfur(S₈) were newly synthesized with ratios of 0.75 wt% and 0.27 wt% with respect to the magnesium sulfate after the ion irradiation with irradiation fluences of 3.6×10¹⁸/cm² and 9.6×10¹⁶/cm², respectively. The lifetime of magnesium sulfate is estimated to be 2.4×10⁷ years on Europa's surface. We are going to conduct the simultaneous irradiation of ions and electrons on icy and sulfuric acid to reproduce more realistic chemical cycles and clarify the source of sulfur on Europa's surface.

・Alvarellos, José Luis, Kevin J. Zahnle, Anthony R. Dobrovolskis, and Patrick Hamill. 2008. “Transfer of Mass from Io to Europa and beyond due to Cometary Impacts.” Icarus 194 (2): 636–46.
・Carlson, R. W., M. S. Anderson, R. E. Johnson, M. B. Schulman, and A. H. Yavrouian. 2002. “Sulfuric Acid Production on Europa: The Radiolysis of Sulfur in Water Ice.” Icarus 157 (2): 456–63.
・Kargel, Jeffrey S., Jonathan Z. Kaye, James W. Head, Giles M. Marion, Roger Sassen, James K. Crowley, Olga Prieto Ballesteros, Steven A. Grant, and David L. Hogenboom. 2000. “Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life.” Icarus 148 (1): 226–65.