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 by 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.

Context. Deuterated ions, especially H 2 D+ and N 2 D + , are abundant in cold (∼10 K), dense (∼10 5 cm −3 ) regions, in which CO is frozen out onto dust grains. In such environments, the N 2 D + /N 2 H + ratio can exceed the elemental abundance ratio of D/H by a factor of 10 4 . Aims. We use deuterium fractionation to investigate the evolutionary state of Class 0 protostars. In particular, we expect the N 2 D + /N 2 H + ratio to decrease as temperature (a sign of the evolution of the protostar) increases. Methods. We observed N 2 H + 1−0, N 2 D + 1−0, 2−1 and 3−2, C 18 O 1−0 and HCO + 3−2 in a sample of 20 Class 0 and borderline Class 0/I protostars. We determined the deuteration fraction and searched for correlations between the N 2 D + /N 2 H + ratio and wellestablished evolutionary tracers, such as T Dust and the CO depletion factor. In addition, we compared the observational result with a chemical model. Results. In our protostellar sample, the N 2 H + 1−0 optical depths are significantly lower than those found in prestellar cores, but the N 2 H + column densities are comparable, which can be explained by the higher temperature and larger line width in protostellar cores. The deuterium fractionation of N 2 H + in protostellar cores is also similar to that in prestellar cores. We found a clear correlation between the N 2 D + /N 2 H + ratio and evolutionary tracers. As expected, the coolest, i.e. the youngest, objects show the largest deuterium fractionation. Furthermore, we find that sources with a high N 2 D + /N 2 H + ratio show clear indications of infall (e.g. δv < 0). With decreasing deuterium fraction, the infall signature disappears and δv tends to be positive for the most evolved objects. The deuterium fractionation of other molecules deviates clearly from that of N 2 H + . The DCO + /HCO + ratio stays low at all evolutionary stages, whereas the NH 2 D/NH 3 ratio is >0.15 even in the most evolved objects. Conclusions. The N 2 D + /N 2 H + ratio is known to trace the evolution of prestellar cores. We show that this ratio can be used to trace core evolution even after star formation. Protostars with an N 2 D + /N 2 H + ratio above 0.15 are in a stage shortly after the beginning of collapse. Later on, deuterium fractionation decreases until it reaches a value of ∼0.03 at the Class 0/I borderline.

Aims. The HIFI instrument onboard Herschel has allowed high spectral resolution and sensitive observations of ground-state transitions of three molecular ions: the methylidyne cation CH + , its isotopologue 13 CH + , and sulfanylium SH + . Because of their unique chemical properties, a comparative analysis of these cations provides essential clues to the link between the chemistry and dynamics of the diffuse interstellar medium. Methods. The CH + , 13 CH + , and SH + lines are observed in absorption towards the distant high-mass star-forming regions (SFRs) DR21(OH), G34.3+0.1, W31C, W33A, W49N, and W51, and towards two sources close to the Galactic centre, SgrB2(N) and SgrA*+50. All sight lines sample the diffuse interstellar matter along pathlengths of several kiloparsecs across the Galactic Plane. In order to compare the velocity structure of each species, the observed line profiles were deconvolved from the hyperfine structure of the SH + transition and the CH + , 13 CH + , and SH + spectra were independently decomposed into Gaussian velocity components. To analyse the chemical composition of the foreground gas, all spectra were divided, in a second step, into velocity intervals over which the CH + , 13 CH + , and SH + column densities and abundances were derived. Results. SH + is detected along all observed lines of sight, with a velocity structure close to that of CH + and 13 CH + . The linewidth distributions of the CH + , SH + , and 13 CH + Gaussian components are found to be similar. These distributions have the same mean ( Δυ ∼ 4.2 km s −1 ) and standard deviation (σ(Δυ) ∼ 1.5 km s −1 ). This mean value is also close to that of the linewidth distribution of the CH + visible transitions detected in the solar neighbourhood. We show that the lack of absorption components narrower than 2 km s −1 is not an artefact caused by noise: the CH + , 13 CH + , and SH + line profiles are therefore statistically broader than those of most species detected in absorption in diffuse interstellar gas (e.g. HCO + , CH, or CN). The SH + /CH + column density ratio observed in the components located away from the Galactic centre spans two orders of magnitude and correlates with the CH + abundance. Conversely, the ratio observed in the components close to the Galactic centre varies over less than one order of magnitude with no apparent correlation with the CH + abundance. The observed dynamical and chemical properties of SH + and CH + are proposed to trace the ubiquitous process of turbulent dissipation, in shocks or shears, in the diffuse ISM and the specific environment of the Galactic centre regions.

We present a comprehensive analysis of a broad band spectral line survey of the Orion Kleinmann-Low nebula (Orion KL), one of the most chemically rich regions in the Galaxy, using the HIFI instrument on board the Herschel Space Observatory. This survey spans a frequency range from 480 to 1907 GHz at a resolution of 1.1 MHz. These observations thus encompass the largest spectral coverage ever obtained toward this high-mass star-forming region in the sub-mm with high spectral resolution, and include frequencies > 1 THz where the Earth's atmosphere prevents observations from the ground. In all, we detect emission from 39 molecules (79 isotopologues). Combining this dataset with ground based mm spectroscopy obtained with the IRAM 30 m telescope, we model the molecular emission from the mm to the far-IR using the XCLASS program which assumes local thermodynamic equilibrium (LTE). Several molecules are also modeled with the MADEX non-LTE code. Because of the wide frequency coverage, our models are constrained by transitions over an unprecedented range

Aims. We aim at deriving the molecular abundances and temperatures of the hot molecular cores in the high-mass star-forming region NGC 6334I and consequently deriving their physical and astrochemical conditions. Methods. In the framework of the Herschel guaranteed time key program CHESS (Chemical HErschel Surveys of Star forming regions), NGC 6334I is investigated by using the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory. A spectral line survey is carried out in the frequency range 480-1907 GHz, and further auxiliary interferometric data from the Submillimeter Array (SMA) in the 230 GHz band provide spatial information for disentangling the different physical components contributing to the HIFI spectrum. The spectral lines in the processed Herschel data are identified with the aid of former surveys and spectral line catalogs. The observed spectrum is then compared to a simulated synthetic spectrum, assuming local thermal equilibrium, and best fit parameters are derived using a model optimization package. Results. A total of 46 molecules are identified, with 31 isotopologues, resulting in about 4300 emission and absorption lines. Highenergy levels (E u > 1000 K) of the dominant emitter methanol and vibrationally excited HCN (ν 2 = 1) are detected. The number of unidentified lines remains low with 75, or <2% of the lines detected. The modeling suggests that several spectral features need two or more components to be fitted properly. Other components could be assigned to cold foreground clouds or to outflows, most visible in the SiO and H 2 O emission. A chemical variation between the two embedded hot cores is found, with more N-bearing molecules identified in SMA1 and O-bearing molecules in SMA2. Conclusions. Spectral line surveys give powerful insights into the study of the interstellar medium. Different molecules trace different physical conditions like the inner hot core, the envelope, the outflows or the cold foreground clouds. The derived molecular abundances provide further constraints for astrochemical models.