The first measurements of the ROSINA instrument of the Rosetta mission reveal that the ratio deuterium / hydrogen (or D/H) of the comet 67P / Churyumov-Gerasimenko is highly enriched in deuterium. These results are in disagreement with the assumptions that assign a cometary origin to the water in the Earth’s atmosphere and oceans. They also indicate that the comets belonging to the 67P family did not originate from a single region, the Kuiper belt: some could come from the Oort cloud. This international study involving laboratories attached to the CNRS, including the IRAP (Université Toulouse III – Paul Sabatier) with the support of the CNES, is published in Science Express of December 10, 2014.
Born 4.55 billion years ago, the various bodies that make up the solar system – Earth, planets, asteroids and comets – initially come from the same gas and dust cloud: the protosolar nebula. From this common origin, they have evolved differently depending on their orbit, and thus their exposure to the solar radiation. Very far from the Sun for most of their lives, comets have hardly evolved and are the privileged witnesses of the conditions that prevailed at the birth of the solar system. The isotopic compositions of their main constituents are therefore likely to provide unique information to describe the conditions and the processes of formation of the solar system, including the origin of water on Earth.
The D/H ratio is a key marker for determining the origin of water on Earth and understanding the roles that have possibly played the comets and/or the asteroids. The detailed study of the first spectra obtained by the ROSINA instrument since its arriving in the vicinity of the comet, has led to a value of the D/H ratio of 5.3 ± 0.7 10-4 while its value for the Earth is 1.55 10-4. This ratio, highly enriched in deuterium compared to the Earth, is therefore not consistent with the hypotheses that attribute a cometary origin to the water in the Earth’s atmosphere and oceans, unlike other results relative to comets of the Jupiter family suggest1. As the value of the Earth’s D/H ratio range between those of the asteroids located between Mars and Jupiter, the water of the Earth’s ocean could thus preferably come from asteroids and/or certain comets. Moreover, the cometary “reservoirs” are located at considerable distances from the Sun: the Oort cloud for example extends over 105 UA2 and is the source of long-period comets like that of Halley. The Kuiper Belt, located more than 50 AU away, is itself known to be at the origin of comets of the 67P / Churyumov-Gerasimenko family called “Jovian comets” because the distant parts of their orbits are close to the orbit of Jupiter. According to the new results of ROSINA, comets of this family do not come from a single source region, the Kuiper belt: some could come from the Oort cloud.
Researchers now want to go on deciphering the chemical and isotopic composition of the atmosphere of 67P / Churyumov-Gerasimenko, including other gaseous species like hydrogen, rare gas or nitrogen. These measurements should help to explore in detail the origin of volatiles on Earth leading to the emergence of life.
1 The D/H ratio of the 103P/Hartley 2 comet is similar to that of the terrestrial oceans
2 1 UA (astronomical unit) = mean Sun-Earth distance – about 150 million kilometers
Implication of the French laboratories in ROSINA
The French researchers involved in the ROSINA instrument of Rosetta belong to the following laboratories :
- Laboratoire atmosphères, milieux, observations spatiales (LATMOS, CNRS/UPMC/UVSQ),
- Institut de recherche en astrophysique et planétologie (IRAP, CNRS/Université Toulouse III – Paul Sabatier).
Both laboratories have been very involved from the start in the realization of the ROSINA experience whose Principal Investigator is Dr. Kathrin Altwegg of the University of Bern.
- Laboratoire de physique et chimie de l’environnement et de l’espace (LPC2E, CNRS/Université d’Orléans),
- Centre de recherches pétrographiques et géochimiques (CRPG, CNRS/Université de Lorraine),
- Laboratoire Univers, transport, interfaces, nanostructures, atmosphère et environnement, molécules (Institut UTINAM, CNRS/Université de Franche-Comté).
This work has benefited from the support of CNES, ESA and the ERC.
- Publication within Science Xpress : 67P/Churyumov-Gerasimenko, a Jupiter Family Comet with a high D/H ratio. Altwegg K. *1, H. Balsiger, A. Bar-Nun, J.J. Berthelier, A. Bieler, P. Bochsler, C. Briois, U. Calmonte, M. Combi, J. De Keyser, P. Eberhardt, B. Fiethe, S. Fuselier, S. Gasc, T. I. Gombosi, K.C. Hansen, M. Hässig, A. Jäckel, E. Kopp, A. Korth, L. LeRoy, U. Mall, B. Marty, O. Mousis, E. Neefs, T. Owen, H. Rème, M. Rubin, T. Sémon, C.-Y. Tzou, H. Waite, P. Wurz. Science express, le 11 décembre 2014.
- ESA Press Release : “Rosetta fuels debate on origin of Earth’s oceans“
- CNRS Press Release : CP-Rosina-VF.docx 718.26 kB
- Henri Rème : Tel : 05 61 55 66 65 / 06 18 58 50 49, Henri.Reme@irap.omp.eu