Deuterium Fractionation: The Ariadne’s Thread from the Precollapse Phase to Meteorites and Comets Today

Abstract

The Solar System formed about 4.6 billion years ago from a condensation of matter inside a molecular cloud. Trying to reconstruct what happened is the goal of this chapter. For that, we put together our understanding of Galactic objects that will eventually form new suns and planetary systems, with our knowledge on comets, meteorites and small bodies of the Solar System today. Our specific tool is the molecular deuteration, namely the amount of deuterium with respect to hydrogen in molecules. This is the Ariadne's thread that helps us to find the way out from a labyrinth of possible histories of our Solar System. The chapter reviews the observations and theories of the deuterium fractionation in pre-stellar cores, protostars, protoplanetary disks, comets, interplanetary dust particles and meteorites and links them together trying to build up a coherent picture of the history of the Solar System formation. We emphasise the interdisciplinary nature of the chapter, which gathers together researchers from different communities with the common goal of understanding the Solar System history.

Cometary Isotopic Measurements

“…Atom addition reactions on dust, primarily starting from condensed CO, can lead to many organic compounds, such as formaldehyde, methanol, formic acid, acetaldehyde, isocyanic acid and formamide, molecules which are also identified in comets (e.g., Herbst and van Dishoeck 2009). High atomic D/H ratios in the condensing gas consequently leads to very high D/H ratios and the formation of many multiply-deuterated isotopologues for surface-formed molecules (Charnley et al 1997); these latter species include D 2 O, D 2 CO, CHD 2 OH, CD 3 OH, NHD 2 , ND 3 and D 2 S (Parise et al 2006;Ceccarelli et al 2014). These characteristics are observed in the interstellar medium and Table 4 summarizes the range of D/H ratios found in cold dark clouds and in cores forming both low-mass and massive protostars.…”

Exploring molecular complexity with ALMA (EMoCA): Deuterated complex organic molecules in Sagittarius B2(N2)

“…Deuteration is a powerful tracer of the history of the cold prestellar phase in star-forming regions (see, e.g., Caselli & Ceccarelli 2012;Ceccarelli et al 2014). At low temperatures and high densities that prevail in prestellar cores, the gas-phase abundance of H + 3 gets enhanced thanks to the depletion of its main destroyer, CO, onto the surface of dust grains.…”

Constraints from Comets on the Formation and Volatile Acquisition of the Planets and Satellites

“…Recently, terrestrial-like D/H ratios have been reported for two comets presumed to be JFCs (Ceccarelli et al 2014;Hartogh et al 2011a), thus revitalizing the theory for a cometary origin for terrestrial oceans. However, the measurement of the D/H ratio of comet 67P/CG counters this argument (Altwegg et al 2015).…”

“…We know a little bit more about the isotopic composition of comets, thanks to spectroscopic measurements of the D/H and N isotopes (Bockelée-Morvan et al 2008;Ceccarelli et al 2014;Hartogh et al 2011a;Manfroid et al 2009;Rousselot et al 2014;Shinnaka et al 2014;Altwegg et al 2015). As described in Sect.…”