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Stability of Sulphur Dimers (S2) in Cometary Ices

Mousis, O. ; Ozgurel, O. ; Lunine, J. I. ; Luspay-Kuti, A. ; Ronnet, T. LU ; Pauzat, F. ; Markovits, A. and Ellinger, Y. (2017) In Astrophysical Journal 835(2).
Abstract

S2 has been observed for decades in comets, including comet 67P/Churyumov-Gerasimenko. Despite the fact that this molecule appears ubiquitous in these bodies, the nature of its source remains unknown. In this study, we assume that S2 is formed by irradiation (photolysis and/or radiolysis) of S-bearing molecules embedded in the icy grain precursors of comets and that the cosmic ray flux simultaneously creates voids in ices within which the produced molecules can accumulate. We investigate the stability of S2 molecules in such cavities, assuming that the surrounding ice is made of H2S or H2O. We show that the stabilization energy of S2 molecules in such voids is close to... (More)

S2 has been observed for decades in comets, including comet 67P/Churyumov-Gerasimenko. Despite the fact that this molecule appears ubiquitous in these bodies, the nature of its source remains unknown. In this study, we assume that S2 is formed by irradiation (photolysis and/or radiolysis) of S-bearing molecules embedded in the icy grain precursors of comets and that the cosmic ray flux simultaneously creates voids in ices within which the produced molecules can accumulate. We investigate the stability of S2 molecules in such cavities, assuming that the surrounding ice is made of H2S or H2O. We show that the stabilization energy of S2 molecules in such voids is close to that of the H2O ice binding energy, implying that they can only leave the icy matrix when this latter sublimates. Because S2 has a short lifetime in the vapor phase, we derive that its formation in grains via irradiation must occur only in low-density environments such as the ISM or the upper layers of the protosolar nebula, where the local temperature is extremely low. In the first case, comets would have agglomerated from icy grains that remained pristine when entering the nebula. In the second case, comets would have agglomerated from icy grains condensed in the protosolar nebula and that would have been efficiently irradiated during their turbulent transport toward the upper layers of the disk. Both scenarios are found consistent with the presence of molecular oxygen in comets.

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author
publishing date
type
Contribution to journal
publication status
published
subject
keywords
astrobiology, comets: general, comets: individual (67P/Churyumov-Gerasimenko), methods: numerical, solid state: volatile
in
Astrophysical Journal
volume
835
issue
2
article number
134
publisher
American Astronomical Society
external identifiers
  • scopus:85012005016
ISSN
0004-637X
DOI
10.3847/1538-4357/aa5279
language
English
LU publication?
no
id
8b6ca38c-8f67-4d7d-8b6b-a21da658b773
date added to LUP
2019-05-29 09:27:55
date last changed
2020-02-19 05:31:22
@article{8b6ca38c-8f67-4d7d-8b6b-a21da658b773,
  abstract     = {<p>S<sub>2</sub> has been observed for decades in comets, including comet 67P/Churyumov-Gerasimenko. Despite the fact that this molecule appears ubiquitous in these bodies, the nature of its source remains unknown. In this study, we assume that S<sub>2</sub> is formed by irradiation (photolysis and/or radiolysis) of S-bearing molecules embedded in the icy grain precursors of comets and that the cosmic ray flux simultaneously creates voids in ices within which the produced molecules can accumulate. We investigate the stability of S<sub>2</sub> molecules in such cavities, assuming that the surrounding ice is made of H<sub>2</sub>S or H<sub>2</sub>O. We show that the stabilization energy of S<sub>2</sub> molecules in such voids is close to that of the H<sub>2</sub>O ice binding energy, implying that they can only leave the icy matrix when this latter sublimates. Because S<sub>2</sub> has a short lifetime in the vapor phase, we derive that its formation in grains via irradiation must occur only in low-density environments such as the ISM or the upper layers of the protosolar nebula, where the local temperature is extremely low. In the first case, comets would have agglomerated from icy grains that remained pristine when entering the nebula. In the second case, comets would have agglomerated from icy grains condensed in the protosolar nebula and that would have been efficiently irradiated during their turbulent transport toward the upper layers of the disk. Both scenarios are found consistent with the presence of molecular oxygen in comets.</p>},
  author       = {Mousis, O. and Ozgurel, O. and Lunine, J. I. and Luspay-Kuti, A. and Ronnet, T. and Pauzat, F. and Markovits, A. and Ellinger, Y.},
  issn         = {0004-637X},
  language     = {eng},
  month        = {02},
  number       = {2},
  publisher    = {American Astronomical Society},
  series       = {Astrophysical Journal},
  title        = {Stability of Sulphur Dimers (S<sub>2</sub>) in Cometary Ices},
  url          = {http://dx.doi.org/10.3847/1538-4357/aa5279},
  doi          = {10.3847/1538-4357/aa5279},
  volume       = {835},
  year         = {2017},
}