Production of Sulfur Allotropes in Electron Irradiated Jupiter Trojans Ice Analogs

Abstract

In this paper, we investigate sulfur chemistry in laboratory analogs of Jupiter Trojans and Kuiper Belt Objects (KBOs). Electron irradiation experiments of CH 3 OH-NH 3 -H 2 O and H 2 S-CH 3 OH-NH 3 -H 2 O ices were conducted to better understand the chemical differences between primordial planetesimals inside and outside the sublimation line of H 2 S. The main goal of this work is to test the chemical plausibility of the hypothesis correlating the color bimodality in Jupiter Trojans with sulfur chemistry in the incipient solar system. Temperature programmed desorption (TPD) of the irradiated mixtures allows the detection of small sulfur allotropes (S 3 and S 4 ) after the irradiation of H 2 S containing ice mixtures. These small, red polymers are metastable and could polymerize further under thermal processing and irradiation, producing larger sulfur polymers (mainly S 8 ) that are spectroscopically neutral at wavelengths above 500 nm. This transformation may affect the spectral reflectance of Jupiter Trojans in a different way compared to KBOs, thereby providing a useful framework for possibly differentiating and determining the formation and history of small bodies. Along with allotropes, we report the production of organosulfur molecules. Sulfur molecules produced in our experiment have been recently detected by Rosetta in the coma of 67P/Churyumov-Gerasimenko. The very weak absorption of sulfur polymers in the infrared range hampers their identification on Trojans and KBOs, but these allotropes strongly absorb light at UV and Visible wavelengths. This suggests that high signal-to-noise ratio UV-Vis spectra of these objects could provide new constraints on their presence.

Dust-to-Gas and Refractory-to-Ice Mass Ratios of Comet 67P/Churyumov-Gerasimenko from Rosetta Observations

“…The abundances of highly volatile molecules like N 2 (Rubin et al 2015) and O 2 (Bieler et al 2015a(Bieler et al , 2015b, and noble gases like Ar , are consistent with formation at extremely low temperatures found in the Kuiper Belt and beyond. The presence of sulfur allotropes and other sulfur-bearing molecules ) is consistent with their formation via radiolytic processes in the presolar cloud and/or the outer protosolar disk, as shown in laboratory experiments (Mahjoub et al 2017), prior to their incorporation in 67P. The isotopic composition of sulfur-bearing molecules ) furthermore suggests a significant contribution of materials extraneous to the solar nebula.…”

High-resolution SOFIA/EXES Spectroscopy of SO2 Gas in the Massive Young Stellar Object MonR2 IRS3: Implications for the Sulfur Budget

“…Future observations of sulfur-containing ices in samples of dense clouds and YSOs by the planned James Webb Space Telescope should help us to confirm this hypothesis. However, the direct detection of sulfur allotropes is unlikely, considering their infrared absorption bands are weak and broad (17-50 µm; e.g., Mahjoub et al 2017). High spectral resolution observations of gas-phase SO 2 with EXES on SOFIA toward a larger sample of YSOs are also needed to further distinguish between quiescent hot core and shocked environments.…”

Visible Near-infrared Spectral Evolution of Irradiated Mixed Ices and Application to Kuiper Belt Objects and Jupiter Trojans

“…The specular-geometry, "thin film" experiments were also used to investigate the chemical constituents formed during irradiation and thermal processing by observation in the midinfrared; these results have been reported by Mahjoub et al (2016) and highlight the critical role that sulfur plays in altering the chemistry of the irradiated ices. Additional sulfur-containing compounds not identified in the mid-infrared were identified by mass spectrometry while heating the samples to room temperature (Mahjoub et al 2017). Thicknesses (and uncertainties) reported in Table 1 were extrapolated from the thin film results of Mahjoub et al (2016) based on the known increase in quantity of gas dosed here.…”