From the Interstellar Medium to Earth's Oceans via Comets—An Isotopic Study of HDO/H2O
✍ Scribed by D. Laufer; G. Notesco; A. Bar-Nun; T. Owen
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 61 KB
- Volume
- 140
- Category
- Article
- ISSN
- 0019-1035
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✦ Synopsis
The isotopic enrichment of HDO over H 2 O when water vapor freezes into ice at 60-170 K was studied experimentally. No such enrichment was detected (1.003-1.007 in the 95% confidence interval). Thus HDO cannot be enriched when ice is formed by freezing of water vapor. The very similar D/H ratio in the water of Comets Halley, Hyakutake, and Hale-Bopp (∼3 × 10 -4 ) is 10-20 times larger then the D/H ratio in the solar nebula. Therefore the cometary water had to originate in a giant molecular cloud, where the HDO is enriched by ion-molecule reactions. We cannot determine whether the ice grains which agglomerated into these comets were formed in a ∼50 K warm clump in the giant molecular cloud and settled intact to the solar nebula or sublimated and refroze in the ∼50 K Uranus-Neptune region. The HDO/H 2 O ratio in Earth's oceans suggests that the water was delivered by both comets and rocky material formed in Earth's region of the solar nebula.