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| Titel |
Constraints on the subsurface structure and density of the nucleus of Comet 67P/Churyumov-Gerasimenko from radar observations |
| VerfasserIn |
Philippe Lamy, Paul Kamoun, Imre Toth, Alain Herique |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092635
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| Publikation (Nr.) |
 EGU/EGU2014-6993.pdf |
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| Zusammenfassung |
| We performed an in-depth analysis of the observations carried with the radar system of the
Arecibo Observatory in November 1982 when comet 67P/Churyumov-Gerasimenko had a
close encounter with Earth at a geocentric distance of 0.4 AU taking into account our present
knowledge of the properties of its nucleus (size, rotational state). In the absence of a
detectable radar echo, we determined a maximum radar cross section of 0.7km2 leading to a
maximum radar albedo of 0.05. This low albedo probably results from a combination of
a low radar reflectivity material and a lightly packed upper layer of the nucleus
with substantial roughness (rms slope of -55°), consistent with its low thermal
inertia. Based on radar observations of other cometary nuclei and asteroids, it is
unlikely that the albedo can be lower than 0.04 so that we were able to constrain
the dielectric permittivity of the subsurface layer to a narrow range of 1.9 to 2.1.
Laboratory measurements and our modeling of mixtures of ice and dust led to a porosity
in the range of approximately 55 to 65% and a density in the range of -600 to
-1000kgm-3 for the top -2.5m layer of the nucleus. This would be the bulk density
range for an homogeneous nucleus and would place the success of the landing at risk
but an inhomogeneous nucleus with an overall density below this range remains a
possibility. |
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