![Infrared spectra of pure H2S (blue) and H2O:H2S (10:1) (red) ice mixtures after UV irradiation followed by warm-up to room temperature, measured at 300 K. The residue from the H2S ice does not show any IR absorption band. Functional groups assigned to bands in the H2O:H2S (10:1) residue are indicated at the top; vibrational bands and assignments are also listed in Table 1, along with possible carrier species or chemical families producing those features. -- [astro-ph.GA]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/Water-.png?fit=1200%2C676&ssl=1)
[astro-ph.GA] Sulfur is the tenth most abundant element in space, yet it is strongly depleted in the gas phase of dense interstellar regions, suggesting sequestration in dust grain components that are difficult to detect.
We study whether UV irradiation and thermal processing of H2S-containing interstellar-ice analogues can produce refractory sulfur species, and whether water-dominated ice enhances their formation.
We performed UV irradiation and warm-up experiments on H2S-containing ice analogues with and without water, and the resulting refractory residues were analysed ex situ. Refractory sulfur species, including the sulfur allotropes S6-S8, are formed during UV irradiation and thermal processing of H2S-containing interstellar-ice analogues.
Water enhances the formation of these sulfur allotropes by two orders of magnitude. We propose a formation mechanism in which ionic intermediates stabilised by the water-ice matrix promote chain growth and cyclisation, yielding predominantly S8.
The combined detection in our residues of sulfur allotropes and polythionic species, also reported in meteorites and samples returned from asteroids, supports their formation in pre-cometary ice mantles covering dust grains.
Because these species can incorporate multiple sulfur atoms per molecule, they constitute an efficient solid-phase reservoir for the missing sulfur in dense cloud environments where young stars are born. Refractory sulfur can therefore serve as a tracer of water-ice environments in space.
Carlos del Burgo Olivares, Hector Carrascosa, Guillermo M. Muñoz Caro, Rafael Lebron-Aguilar, Jose E. Quintanilla-Lopez, Yao-Jen Chen
Comments: Accepted for publication in Astronomy & Astrophysics (A&A). 5 figures, 1 table
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2610.00449 [astro-ph.GA] (or arXiv:2610.00449v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2610.00449
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Submission history
From: Carlos Del Burgo Olivares
[v1] Wed, 30 Sep 2026 17:58:50 UTC (3,177 KB)
https://arxiv.org/abs/2610.00449
Astrobiology, Astrochemistry,
