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Synthesis of Molecular Oxygen via Irradiation of Ice Grains in the Protosolar Nebula

Mousis, O. ; Ronnet, T. LU ; Lunine, J. I. ; Maggiolo, R. ; Wurz, P. ; Danger, G. and Bouquet, A. (2018) In Astrophysical Journal 858(1).
Abstract

Molecular oxygen has been detected in the coma of comet 67P/Churyumov-Gerasimenko with a mean abundance of 3.80 ±0.85% by the ROSINA mass spectrometer on board the Rosetta spacecraft. To account for the presence of this species in comet 67P/Churyumov-Gerasimenko, it has been shown that the radiolysis of ice grain precursors of comets is a viable mechanism in low-density environments, such as molecular clouds. Here, we investigate the alternative possibility that the icy grains present in the midplane of the protosolar nebula were irradiated during their vertical transport between the midplane and the upper layers over a large number of cycles, as a result of turbulent mixing. Consequently, these grains spent a non-negligible fraction of... (More)

Molecular oxygen has been detected in the coma of comet 67P/Churyumov-Gerasimenko with a mean abundance of 3.80 ±0.85% by the ROSINA mass spectrometer on board the Rosetta spacecraft. To account for the presence of this species in comet 67P/Churyumov-Gerasimenko, it has been shown that the radiolysis of ice grain precursors of comets is a viable mechanism in low-density environments, such as molecular clouds. Here, we investigate the alternative possibility that the icy grains present in the midplane of the protosolar nebula were irradiated during their vertical transport between the midplane and the upper layers over a large number of cycles, as a result of turbulent mixing. Consequently, these grains spent a non-negligible fraction of their lifetime in the disk's upper regions, where the irradiation by cosmic rays was strong. To do so, we used a coupled disk-transport-irradiation model to calculate the time evolution of the molecular oxygen abundance radiolytically produced in ice grains. Our computations show that, even if a significant fraction of the icy particles has followed a back and forth cycle toward the upper layers of the disk over tens of millions of years, a timespan far exceeding the formation timescale of comet 67P/Churyumov-Gerasimenko, the amount of produced molecular oxygen is at least two orders of magnitude lower than the Rosetta observations. We conclude that the most likely scenario remains the formation of molecular oxygen in low-density environments, such as the presolar cloud, prior to the genesis of the protosolar nebula.

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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
858
issue
1
article number
66
publisher
American Astronomical Society
external identifiers
  • scopus:85047213036
ISSN
0004-637X
DOI
10.3847/1538-4357/aab6b9
language
English
LU publication?
no
id
bae094e5-bbf9-4ceb-abc4-e4c1e24fb8d5
date added to LUP
2019-05-29 09:24:50
date last changed
2020-02-19 05:31:23
@article{bae094e5-bbf9-4ceb-abc4-e4c1e24fb8d5,
  abstract     = {<p>Molecular oxygen has been detected in the coma of comet 67P/Churyumov-Gerasimenko with a mean abundance of 3.80 ±0.85% by the ROSINA mass spectrometer on board the Rosetta spacecraft. To account for the presence of this species in comet 67P/Churyumov-Gerasimenko, it has been shown that the radiolysis of ice grain precursors of comets is a viable mechanism in low-density environments, such as molecular clouds. Here, we investigate the alternative possibility that the icy grains present in the midplane of the protosolar nebula were irradiated during their vertical transport between the midplane and the upper layers over a large number of cycles, as a result of turbulent mixing. Consequently, these grains spent a non-negligible fraction of their lifetime in the disk's upper regions, where the irradiation by cosmic rays was strong. To do so, we used a coupled disk-transport-irradiation model to calculate the time evolution of the molecular oxygen abundance radiolytically produced in ice grains. Our computations show that, even if a significant fraction of the icy particles has followed a back and forth cycle toward the upper layers of the disk over tens of millions of years, a timespan far exceeding the formation timescale of comet 67P/Churyumov-Gerasimenko, the amount of produced molecular oxygen is at least two orders of magnitude lower than the Rosetta observations. We conclude that the most likely scenario remains the formation of molecular oxygen in low-density environments, such as the presolar cloud, prior to the genesis of the protosolar nebula.</p>},
  author       = {Mousis, O. and Ronnet, T. and Lunine, J. I. and Maggiolo, R. and Wurz, P. and Danger, G. and Bouquet, A.},
  issn         = {0004-637X},
  language     = {eng},
  month        = {05},
  number       = {1},
  publisher    = {American Astronomical Society},
  series       = {Astrophysical Journal},
  title        = {Synthesis of Molecular Oxygen via Irradiation of Ice Grains in the Protosolar Nebula},
  url          = {http://dx.doi.org/10.3847/1538-4357/aab6b9},
  doi          = {10.3847/1538-4357/aab6b9},
  volume       = {858},
  year         = {2018},
}