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A primordial origin for molecular oxygen in comets: A chemical kinetics study of the formation and survival of O$_2$ ice from clouds to disks
- Source :
- Monthly Notices of the Royal Astronomical Society, 462, S99-S115, Monthly Notices of the Royal Astronomical Society
- Publication Year :
- 2016
- Publisher :
- arXiv, 2016.
-
Abstract
- Molecular oxygen has been confirmed as the fourth most abundant molecule in cometary material O$_2$/H$_2$O $\sim 4$ %) and is thought to have a primordial nature, i.e., coming from the interstellar cloud from which our solar system was formed. However, interstellar O$_2$ gas is notoriously difficult to detect and has only been observed in one potential precursor of a solar-like system. Here, the chemical and physical origin of O$_2$ in comets is investigated using sophisticated astrochemical models. Three origins are considered: i) in dark clouds, ii) during forming protostellar disks, and iii) during luminosity outbursts in disks. The dark cloud models show that reproduction of the observed abundance of O$_2$ and related species in comet 67P/C-G requires a low H/O ratio facilitated by a high total density ($\geq 10^5$ cm$^{-3}$), and a moderate cosmic ray ionisation rate ($\leq 10^{-16}$ s$^{-1}$) while a temperature of 20 K, slightly higher than the typical temperatures found in dark clouds, also enhances the production of O$_2$. Disk models show that O$_2$ can only be formed in the gas phase in intermediate disk layers, and cannot explain the strong correlation between O$_2$ and H$_2$O in comet 67P/C-G together with the weak correlation between other volatiles and H$_2$O. However, primordial O$_2$ ice can survive transport into the comet-forming regions of disks. Taken together, these models favour a dark cloud (or "primordial") origin for O$_2$ in comets, albeit for dark clouds which are warmer and denser than those usually considered as solar system progenitors.<br />Comment: Accepted for publication in MNRAS. 20 pages, 13 figures, 2 tables
- Subjects :
- Physics
Solar System
Astrochemistry
010504 meteorology & atmospheric sciences
Interstellar cloud
Comet
Astronomy
FOS: Physical sciences
Astronomy and Astrophysics
Cosmic ray
Astrophysics
01 natural sciences
Astrophysics - Astrophysics of Galaxies
Luminosity
13. Climate action
Space and Planetary Science
Interstellar comet
Ionization
Astrophysics of Galaxies (astro-ph.GA)
0103 physical sciences
010303 astronomy & astrophysics
0105 earth and related environmental sciences
Subjects
Details
- Database :
- OpenAIRE
- Journal :
- Monthly Notices of the Royal Astronomical Society, 462, S99-S115, Monthly Notices of the Royal Astronomical Society
- Accession number :
- edsair.doi.dedup.....9d389a75acbb52fc8c92d0cc729b83c6
- Full Text :
- https://doi.org/10.48550/arxiv.1608.07130