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Herschel measurements of the D/H and ^(16)O/^(18)O ratios in water in the Oort-cloud comet C/2009 P1 (Garradd)

Bockelée-Morvan, D. and Biver, N. and Swinyard, B. and de Val-Borro, M. and Crovisier, J. and Hartogh, P. and Lis, D. C. and Moreno, R. and Szutowicz, S. and Lellouch, E. and Emprechtinger, M. and Blake, G. A. and Courtin, R. and Jarchow, C. and Kidger, M. and Küppers, M. and Rengel, M. and Davis, G. R. and Fulton, T. and Naylor, D. and Sidher, S. and Walker, H. (2012) Herschel measurements of the D/H and ^(16)O/^(18)O ratios in water in the Oort-cloud comet C/2009 P1 (Garradd). Astronomy and Astrophysics, 544 . Art. No. L15. ISSN 0004-6361.

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The D/H ratio in cometary water is believed to be an important indicator of the conditions under which icy planetesimals formed and can provide clues to the contribution of comets to the delivery of water and other volatiles to Earth. Available measurements suggest that there is isotopic diversity in the comet population. The Herschel Space Observatory revealed an ocean-like ratio in the Jupiter-family comet 103P/Hartley 2, whereas most values measured in Oort-cloud comets are twice as high as the ocean D/H ratio. We present here a new measurement of the D/H ratio in the water of an Oort-cloud comet. HDO, H_2O, and H_2^(18) lines were observed with high signal-to-noise ratio in comet C/2009 P1 (Garradd) using the Herschel HIFI instrument. Spectral maps of two water lines were obtained to constrain the water excitation. The D/H ratio derived from the measured H_2^(16)O and HDO production rates is (2.06 ± 0.22) × 10^(-4). This result shows that the D/H in the water of Oort-cloud comets is not as high as previously thought, at least for a fraction of the population, hence the paradigm of a single, archetypal D/H ratio for all Oort-cloud comets is no longer tenable. Nevertheless, the value measured in C/2009 P1 (Garradd) is significantly higher than the Earth’s ocean value of 1.558 × 10^(-4). The measured ^(16)O/^(18)O ratio of 523 ± 32 is, however, consistent with the terrestrial value.

Item Type:Article
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URLURL TypeDescription
Lis, D. C.0000-0002-0500-4700
Blake, G. A.0000-0003-0787-1610
Additional Information:© 2012 ESO. Received 4 June 2012. Accepted 24 July 2012. Published online 10 August 2012. Herschel is an ESA space observatory with science instruments provided by European-led principal investigator consortia and with important contribution from NASA. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States (NASA) under the leadership of SRON, Netherlands Institute for Space Research, Groningen, The Netherlands, and with major contributions from Germany, France and the US. Support for this work was provided by NASA through an award issued by JPL/Caltech. S.S. was supported by polish MNiSW funds (181/N-HSO/2008/0).
Funding AgencyGrant Number
Ministerstwo Nauki i Szkolnictwa Wyższego (MNiSW)181/N-HSO/2008/0
Subject Keywords:comets: general; submillimeter: planetary systems; astrochemistry; comets: individual: C/2009 P1 (Garradd); Oort cloud
Record Number:CaltechAUTHORS:20121009-081112536
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Official Citation:Herschel measurements of the D/H and 16O/18O ratios in water in the Oort-cloud comet C/2009 P1 (Garradd) L15 D. Bockelée-Morvan, N. Biver, B. Swinyard, M. de Val-Borro, J. Crovisier, P. Hartogh, D. C. Lis, R. Moreno, S. Szutowicz, E. Lellouch, et al. (12 more) Published online: 10 August 2012 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34770
Deposited By: Ruth Sustaita
Deposited On:09 Oct 2012 16:23
Last Modified:03 Oct 2019 04:22

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