Publication date: 13 Oct 2011

Authors: Hartogh, P., et al.

Journal: Nature
Volume: 478
Issue: 7368
Page: 218-220
Year: 2011

Copyright: Nature Publishing Group

Published online on 5 October 2011.

For decades, the source of Earth's volatiles, especially water with a deuterium-to-hydrogen ratio (D/H) of (1.558±0.001)×10^-4, has been a subject of debate. The similarity of Earth's bulk composition to that of meteorites known as enstatite chondrites suggests a dry proto-Earth with subsequent delivery of volatiles via local accretion or impacts of asteroids or comets. Previous measurements in six comets from the Oort cloud yielded a mean D/H ratio of (2.96±0.25)×10^-4. The D/H value in carbonaceous chondrites, (1.4±0.1)×10^-4, together with dynamical simulations, led to models in which asteroids were the main source of Earth's water, with <10 per cent being delivered by comets. Here we report that the D/H ratio in the Jupiter-family comet 103P/Hartley 2, which originated in the Kuiper belt, is (1.61±0.24)×10^-4. This result substantially expands the reservoir of Earth ocean-like water to include some comets, and is consistent with the emerging picture of a complex dynamical evolution of the early Solar System.

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