Sulfur Ice Astrochemistry: A Review of Laboratory Studies

Abstract

Sulfur is the tenth most abundant element in the universe and is known to play a significant role in biological systems. Accordingly, in recent years there has been increased interest in the role of sulfur in astrochemical reactions and planetary geology and geochemistry. Among the many avenues of research currently being explored is the laboratory processing of astrophysical ice analogues. Such research involves the synthesis of an ice of specific morphology and chemical composition at temperatures and pressures relevant to a selected astrophysical setting (such as the interstellar medium or the surfaces of icy moons). Subsequent processing of the ice under conditions that simulate the selected astrophysical setting commonly involves radiolysis, photolysis, thermal processing, neutral-neutral fragment chemistry, or any combination of these, and has been the subject of several studies. The in-situ changes in ice morphology and chemistry occurring during such processing are often monitored via spectroscopic or spectrometric techniques. In this paper, we have reviewed the results of laboratory investigations concerned with sulfur chemistry in several astrophysical ice analogues. Specifically, we review (i) the spectroscopy of sulfur-containing astrochemical molecules in the condensed phase, (ii) atom and radical addition reactions, (iii) the thermal processing of sulfur-bearing ices, (iv) photochemical experiments, (v) the non-reactive charged particle radiolysis of sulfur-bearing ices, and (vi) sulfur ion bombardment of and implantation in ice analogues. Potential future studies in the field of solid phase sulfur astrochemistry are also discussed in the context of forthcoming space missions, such as the NASA James Webb Space Telescope and the ESA Jupiter Icy Moons Explorer mission.

Electron irradiation and thermal chemistry studies of interstellar and planetary ice analogues at the ICA astrochemistry facility

“…In this section, we outline the results of thermal reactions occurring in a mixed ice containing H 2 O and SO 2 . Thermal reactions involving sulphur-bearing molecules (such as SO 2 ) are especially relevant to astrochemical and astrobiological studies of Solar System bodies such as Mars and the Galilean moons of Jupiter [27]. Previous studies have revealed that thermal reactions take place in mixed ices of SO 2 and H 2 O, with the primary product being bisulphite (HSO − 3 ) alongside a smaller quantity of meta-bisulphite (S 2 O 2− 5 ) [28,29].…”

The Role of Terahertz and Far-IR Spectroscopy in Understanding the Formation and Evolution of Interstellar Prebiotic Molecules

“…The unambiguous identification of such molecules by infrared and radio telescopes (including those which operate in the THz/F-IR range) relies on the availability and completeness of gas-and solid-phase spectroscopic databases at the corresponding frequencies for a great variety of molecules. Such information is obtained by performing classical laboratory measurements (Wlodarczak 1995;Smith 2011;Cataldo et al, 2013a;Allodi et al, 2013;Widicus-Weaver 2019;Mifsud et al, 2021). Presently, the two most commonly referenced catalogues are the Cologne Database for Molecular Spectroscopy (Müller et al, 2001;Endres et al, 2016) and the Jet Propulsion Laboratory (Pickett et al, 1998) catalogues, which give the frequency and amplitude of several molecular transitions.…”

Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide

“…The presence of a distributed source of CS in the coma is not surprising in the context of other product species found in comets (e.g., H 2 CO, HNC) as well as unresolved questions regarding the sulfur inventory of various astronomical sources. An observed depletion of gas-phase sulfur-bearing species in dense clouds and star-forming regions along with a depletion of ice-phase sulfur-bearing molecules in the interstellar medium has resulted in a search for "missing sulfur" (Mifsud et al 2021). Similar to the unknown refractory parent suggested for H 2 CO (Section 4.3) and the refractory ammonium salts identified as potential reservoirs for the "missing nitrogen" in comets (Altwegg et al 2020), an unidentified refractory sulfur-bearing component has been suggested to address the observed sulfur depletion.…”