Water in protoplanetary disks: Deuteration and turbulent mixing
- Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan)
- Department of Astronomy, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)
- University of Bordeaux, LAB, UMR 5804, F-33270 Floirac (France)
We investigate water and deuterated water chemistry in turbulent protoplanetary disks. Chemical rate equations are solved with the diffusion term, mimicking turbulent mixing in a vertical direction. Water near the midplane is transported to the disk atmosphere by turbulence and is destroyed by photoreactions to produce atomic oxygen, while the atomic oxygen is transported to the midplane and reforms water and/or other molecules. We find that this cycle significantly decreases column densities of water ice at r ≲ 30 AU, where dust temperatures are too high to reform water ice effectively. The radial extent of such region depends on the desorption energy of atomic hydrogen. Our model indicates that water ice could be deficient even outside the sublimation radius. Outside this radius, the cycle decreases the deuterium-to-hydrogen (D/H) ratio of water ice from ∼2 × 10{sup –2}, which is set by the collapsing core model, to 10{sup –4}-10{sup –2} in 10{sup 6} yr, without significantly decreasing the water ice column density. The resultant D/H ratios depend on the strength of mixing and the radial distance from the central star. Our finding suggests that the D/H ratio of cometary water (∼10{sup –4}) could be established (i.e., cometary water could be formed) in the solar nebula, even if the D/H ratio of water ice delivered to the disk was very high (∼10{sup –2}).
- OSTI ID:
- 22348558
- Journal Information:
- Astrophysical Journal, Vol. 779, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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