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

Mousis, O.; Ronnet, T.; Lunine, J. I.; Maggiolo, R.; Wurz, Peter; Danger, G.; Bouquet, A. (2018). Synthesis of Molecular Oxygen via Irradiation of Ice Grains in the Protosolar Nebula. Astrophysical journal, 858(1), p. 66. Institute of Physics Publishing IOP 10.3847/1538-4357/aab6b9

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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-transportirradiation
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.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Wurz, Peter

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

0004-637X

Publisher:

Institute of Physics Publishing IOP

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

04 Jun 2018 14:18

Last Modified:

23 Oct 2019 14:54

Publisher DOI:

10.3847/1538-4357/aab6b9

BORIS DOI:

10.7892/boris.116944

URI:

https://boris.unibe.ch/id/eprint/116944

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