Ocean-Like Water in the Jupiter Family Comet 103P/Hartley 2
Abstract
Comets are among the most primitive bodies left from the planetesimal building stage of the Solar Nebula. Submillimeter wavelengths are well matched to the cold environments of cometary atmospheres (T ∼ 40-100 K). Over two dozens of molecules have been detected in comets, primarily by means of (sub)millimeter spectroscopy. Measurements of isotopic ratios, in particular D/H, provide key information about the origin and evolution of cometary ices and possible links with the interstellar medium. The D/H ratio in water in long period, Oort cloud comets, ∼ 3 × 10-4, corresponds to a factor of ∼ 12 enrichment over the protosolar value and twice the Earth ocean ratio, VSMOW 1.56 × 10-4. These measurements imply that comets incorporated material partially reprocessed in the inner Solar Nebula and could have contributed at most ∼ 10% of the Earth ocean water. Using Herschel/HIFI, we have measured for the first time the D/H ratio in a Jupiter family comet, originating from a different, large reservoir of water ice rich material---the Kuiper belt. We derive a D/H ratio in water of (1.6±0.24)×10-4 (1σ), a factor of 2 lower than the earlier measurements in Oort cloud comets and the same as VSMOW. This indicates that the high D/H values previously measured in Oort cloud comets are not representative of all comets and that the current understanding of deuteration in different solar system reservoirs, or solar system dynamics, is incomplete and has to be revisited. Furthermore, comets similar to Hartley 2 could have delivered a much higher fraction of the Earth ocean water than previously thought.
- Publication:
-
From Atoms to Pebbles: Herschel's view of Star and Planet Formation
- Pub Date:
- March 2012
- Bibcode:
- 2012faph.confE..46L