On the colors of Jupiter's satellite Io: Irradiation of solid sulfur at 77 K

Abstract

The colors of seven sulfur allotropes at 77 K have been investigated both before and after irradiation by a high‐pressure mercury lamp. S8 is white at 77 K but turns intense yellow within a few minutes on irradiation through quartz or DURAN. On warming, the yellow species (presumably chain‐like sulfur diradicals characterized by an absorption at 430 nm) decomposes near 260 K and polymeric sulfur (S∞) is formed; the sample color changes gradually to the very similar color of an S8–S∞ mixture, resulting in no visually detectable color change with temperature from 77 K to 260 K. This is consistent with the lack of posteclipse brightening on Io. Other sulfur forms also turn intense yellow (S7, S10), grayish yellow (S12, S20, S∞), or brownish yellow (S6) on irradiation at 77 K, and these colors also change to the normal colors of the starting materials on warming to 298 K. We suggest that the yellowish features on Io are caused by the effect of solar radiation on elemental sulfur. The yellow color thus produced may subsequently be modified by deposits of SO2 frosts and volcanic ash.

S2O, polysulfuroxide and sulfur polymer on Io's surface?

“…If this liquid is rapidly cooled to low temperatures, as probably for Io's lavas (outer layers of the flows at least), the mixture is quenched and the solid formed contains important amounts of sulfur polymer (Moses and Nash, 1991). Moreover, when S 8 or other cyclic sulfur allotropes are condensed at low temperature and irradiated, part of the sulfur is transformed into sulfur polymer (Steudel et al, 1986;Steudel and Eckert, 2003). All these chemical and physicochemical arguments point to the very likely presence of sulfur polymer on Io's surface.…”

Photochemistry of a Volcanically Driven Atmosphere on Io: Sulfur and Oxygen Species from a Pele-Type Eruption

“…If SO partially condenses into S 2 O (with possible S 3 and S 4 production during the process), then condensed SO might help explain the appearance of the polar regions. If SO condenses into polysulfur oxides, then polysulfur oxides are still viable candidates for the yellow regions seen all over Io (Geissler et al 1999a, McEwen et al 1998a, as is elemental sulfur (S 8 ) that has been irradiated by ultraviolet light; see Steudel et al (1986).…”

The Zamama–Thor region of Io: Insights from a synthesis of mapping, topography, and Galileo spacecraft data

“…For example, irradiation of pale yellow S 8 results in the development of the metastable short-chain molecules S 3 and S 4 , which range from brownish-yellow to grayish-yellow to orange (Nash and Fanale, 1977;Nelson and Hapke, 1978;Steudel et al, 1986;Hapke and Graham, 1989;Nelson et al, 1990). Red materials tend to be very ephemeral, and fade over a period of a few months at most vents (McEwen et al, 1998a;Geissler et al, 2004).…”