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| Titel |
Seasonal effects on the nucleus of comet 67P revealed by Rosetta/VIRTIS |
| VerfasserIn |
Federico Tosi, Fabrizio Capaccioni, Gianrico Filacchione, Stephane Erard, Batiste Rouseeau, Jean-Philippe Combe, Maria Teresa Capria, Cedric Leyrat, Andrea Longobardo, Dominique Bockelee-Morvan, David Kappel, Gabriele Arnold, Sergio Fonti, Francesca Mancarella, Ekkehard Kuehrt, Stefano Mottola |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250136348
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| Publikation (Nr.) |
 EGU/EGU2016-17371.pdf |
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| Zusammenfassung |
| We describe thermal effects on the nucleus of comet 67P. Due to the overall low thermal
inertia of the nucleus surface, the surface temperature is essentially dominated by the
instantaneous value of the solar incidence angle and the heliocentric distance. However, for
each location, the smallest achievable value of insolation angle depends on the season and
topography. Given the substantial obliquity of comet 67P, seasons are such that the northern
hemisphere is mainly illuminated at aphelion while the southern hemisphere receives most
insolation soon after perihelion. In addition, the heliocentric distance strongly affects the
surface temperature, all other parameters being equal. This is a larger effect in comets
than in asteroids, due to the wide range of heliocentric distance values spanned by
comets.
When Rosetta started its global mapping observation campaign, in early August 2014,
hyperspectral images acquired by the VIRTIS imaging spectrometer onboard the Rosetta
Orbiter covered only the northern regions of the cometary surface, and the equatorial belt
became gradually unveiled, while the southern region has been revealed from 2015
onwards. In parallel, the comet’s heliocentric distance has been decreasing from ∼3.6
AU down to 1.24 AU, the distance at which the perihelion passage occurred on 13
August 2015. By relating surface temperatures as measured by VIRTIS to three
variables: solar incidence angle, true local solar time and heliocentric distance,
we aim to separate the relative contributions due to season and to the heliocentric
distance.
To do this, we use both VIRTIS-M data (namely data from the mapping spectrometer
covering the 1-5 μm range, available up to April 2015, i.e. before the failure of the
IR cryocooler) and VIRTIS-H data (namely data from the high-resolution point
spectrometer covering the 2-5 μm range), and we focus in particular on three regions: one
in the northern hemisphere, one in the equatorial region and one in the southern
hemisphere. These three regions are chosen so as to be relatively smooth at the spatial
resolution that is achieved from a distance of about 100 km (25 m/px for VIRTIS-M,
50×150 m/px for VIRTIS-H), in order to limit the effects of large-scale surface
roughness.
Acknowledgements: The authors would like to thank the following institutions and agencies,
which supported this work: Italian Space Agency (ASI - Italy), Centre National d’Etudes
Spatiales (CNES- France), Deutsches Zentrum für Luft- und Raumfahrt (DLR-Germany),
National Aeronautic and Space Administration (NASA-USA) Rosetta Program, Science and
Technology Facilities Council (UK). VIRTIS has been built by a consortium, which includes
Italy, France and Germany, under the scientific responsibility of the Istituto di Astrofisica e
Planetologia Spaziali of INAF, Italy, which guides also the scientific operations. The VIRTIS
instrument development has been funded and managed by ASI, with contributions from
Observatoire de Meudon financed by CNES, and from DLR. The computational
resources used in this research have been supplied by INAF-IAPS through the DataWell
project. |
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