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|Title:||First observations of H2O and CO2 vapor in comet 67P/Churyumov-Gerasimenko made by VIRTIS onboard Rosetta||Authors:||Bockelée-Morvan, D.
DE SANCTIS, MARIA CRISTINA
Taylor, F. W.
Capria, M. -T.
Reess, J. -M.
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||583||First Page:||A6||Abstract:||Context. Outgassing from cometary nuclei involves complex surface and subsurface processes that need to be understood to investigate the composition of cometary ices from coma observations. Aims: We investigate the production of water, carbon dioxide, and carbon monoxide from the nucleus of comet 67P/Churyumov-Gerasimenko (67P). These species have different volatility and are key species of cometary ices. Methods: Using the high spectral-resolution channel of the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H), we observed the ν<SUB>3</SUB> vibrational bands of H<SUB>2</SUB>O and CO<SUB>2</SUB> at 2.67 and 4.27 μm, respectively, from 24 November 2014 to 24 January 2015, when comet 67P was between 2.91 and 2.47 AU from the Sun. Observations were undertaken in limb-viewing geometry at distances from the surface of 0 to 1.5 km and with various line-of-sight (LOS) orientations in the body-fixed frame. A geometry tool was used to characterize the position of the LOS with respect to geomorphologic regions and the illumination properties of these regions. <BR /> Results: The water production of 67P did not increase much from 2.9 to 2.5 AU. High water column densities are observed for LOS above the neck regions, suggesting they are the most productive in water vapor. While water production is weak in regions with low solar illumination, CO<SUB>2</SUB> is outgassing from both illuminated and non-illuminated regions, which indicates that CO<SUB>2</SUB> sublimates at a depth that is below the diurnal skin depth. The CO<SUB>2</SUB>/H<SUB>2</SUB>O column density ratio varies from 2 to 60%. For regions that are in sunlight, mean values between 2 and 7% are measured. The lower bound value is likely representative of the CO<SUB>2</SUB>/H<SUB>2</SUB>O production rate ratio from the neck regions. For carbon monoxide, we derive column density ratios CO/H<SUB>2</SUB>O < 1.9% and CO/CO<SUB>2</SUB>< 80%. An illumination-driven model, with a uniformly active surface releasing water at a mean rate of 8 × 10<SUP>25</SUP> s<SUP>-1</SUP>, provides an overall agreement to VIRTIS-H data, although some mismatches show local surface inhomogeneities in water production. Rotational temperatures of 90-100 K are derived from H<SUB>2</SUB>O and CO<SUB>2</SUB> averaged spectra.||Acknowledgments:||The authors would like to thank the following institutions and agencies that supported this work: Italian Space Agency (ASI–Italy), Centre National d’Études Spatiales (CNES- France), Deutsches Zentrum fuer Luft- und Raumfahrt (DLR-Germany), National Aeronautic and Space Administration (NASA-USA). VIRTIS was built by a consortium from Italy, France and Germany, under the scientific responsibility of the Istituto di Astrofisica e Planetologia Spaziali of INAF, Rome (IT), which also leads the scientific operations. The VIRTIS instrument development for ESA has been funded and managed by ASI, with contributions from Observatoire de Meudon financed by CNES and from DLR. The instrument industrial prime contractor was former Officine Galileo, now Selex ES (Finmeccanica Group) in Campi Bisenzio, Florence, IT. The authors wish to thank the Rosetta Science Ground Segment and the Rosetta Mission Operations Centre for their fantastic support throughout the early phases of the mission. The VIRTIS calibrated data will be available through the ESA’s Planetary Science Archive (PSA) website. In fond memory of Angioletta Coradini, conceiver of the VIRTIS instrument, our leader and friend.||URI:||http://hdl.handle.net/20.500.12386/23211||URL:||https://www.aanda.org/articles/aa/abs/2015/11/aa26303-15/aa26303-15.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201526303||Bibcode ADS:||2015A&A...583A...6B||Fulltext:||open|
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