A Laboratory Study of 12CO/13CO Ice-Gas Fractionation in Interstellar Ice Analogues
Abstract
Understanding carbon chemistry in forming planetary systems is a critical step toward establishing detailed formation pathways for solar system planets, exoplanets and their atmospheres, and prebiotic molecules. Carbon monoxide (CO) is a key tracer of this evolution, as it is a large reservoir of nebular carbon, and can be observed astronomically. High-resolution observations of CO isotopologues toward a range of young stellar objects (YSOs) have revealed heterogeneity in gas-phase [12C16O/13C16O] (heretofore 12CO/13CO), with values ranging from 85 to 165. Comparison of the CO ice fraction ([12CO] Ice/[12CO] Ice + [12CO] Gas) with gas-phase [12CO]/[13CO] suggests that CO ice may influence gas-phase reservoirs in the YSOs. Toward exploring potential preferential fractionation of 12CO versus 13CO, we conducted thermal desorption and photodesorption experiments in the Ice Spectroscopy Lab at JPL, using astrophysical temperatures ( 10 to 35 K) and pressures ( 10-9 mbar). Infrared spectroscopy was used to examine ice composition and abundance, and mass spectrometry monitored desorbed CO and residual gas in the vacuum chamber. CO ice was prepared (thicknesses 0.2 to 200 μm) through gas-phase deposition of 12CO and 13CO at 20 K. CO ice was slowly warmed up to different set temperatures and spectra were taken at each interval to measure changes in the CO ice. Our latest results show that 12CO vs. 13CO sublimation is identical except for a 0.1 K delay in the 13CO sublimation curve: 12CO (13CO) complete sublimation at 28.9 (29.0) K and 50% depletion at 28.6 (28.7) K. Our sublimation curves for 12CO and 13CO are used as benchmarks for the ongoing photodesorption and photodissociation experiments of pure CO ice, as well as CO trapped CO2 and H2O ice mixtures to study isotopic fractionation by Ly-α radiation (121.6 nm), a major component of the background radiation in protoplanetary environments. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). Funds were provided through NASA Emerging Worlds Program.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5011301S