Publication Date:
2015-01-28
Description:
Comets are composed of dust and frozen gases. The ices are mixed with the refractory material either as an icy conglomerate, or as an aggregate of pre-solar grains (grains that existed prior to the formation of the Solar System), mantled by an ice layer. The presence of water-ice grains in periodic comets is now well established. Modelling of infrared spectra obtained about ten kilometres from the nucleus of comet Hartley 2 suggests that larger dust particles are being physically decoupled from fine-grained water-ice particles that may be aggregates, which supports the icy-conglomerate model. It is known that comets build up crusts of dust that are subsequently shed as they approach perihelion. Micrometre-sized interplanetary dust particles collected in the Earth's stratosphere and certain micrometeorites are assumed to be of cometary origin. Here we report that grains collected from the Jupiter-family comet 67P/Churyumov-Gerasimenko come from a dusty crust that quenches the material outflow activity at the comet surface. The larger grains (exceeding 50 micrometres across) are fluffy (with porosity over 50 per cent), and many shattered when collected on the target plate, suggesting that they are agglomerates of entities in the size range of interplanetary dust particles. Their surfaces are generally rich in sodium, which explains the high sodium abundance in cometary meteoroids. The particles collected to date therefore probably represent parent material of interplanetary dust particles. This argues against comet dust being composed of a silicate core mantled by organic refractory material and then by a mixture of water-dominated ices. At its previous recurrence (orbital period 6.5 years), the comet's dust production doubled when it was between 2.7 and 2.5 astronomical units from the Sun, indicating that this was when the nucleus shed its mantle. Once the mantle is shed, unprocessed material starts to supply the developing coma, radically changing its dust component, which then also contains icy grains, as detected during encounters with other comets closer to the Sun.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schulz, Rita -- Hilchenbach, Martin -- Langevin, Yves -- Kissel, Jochen -- Silen, Johan -- Briois, Christelle -- Engrand, Cecile -- Hornung, Klaus -- Baklouti, Donia -- Bardyn, Anais -- Cottin, Herve -- Fischer, Henning -- Fray, Nicolas -- Godard, Marie -- Lehto, Harry -- Le Roy, Lena -- Merouane, Sihane -- Orthous-Daunay, Francois-Regis -- Paquette, John -- Ryno, Jouni -- Siljestrom, Sandra -- Stenzel, Oliver -- Thirkell, Laurent -- Varmuza, Kurt -- Zaprudin, Boris -- England -- Nature. 2015 Feb 12;518(7538):216-8. doi: 10.1038/nature14159. Epub 2015 Jan 26.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉European Space Agency, Scientific Support Office, Keplerlaan 1, Postbus 299, 2200 AG Noordwijk, The Netherlands. ; Max-Planck-Institut fur Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Gottingen, Germany. ; Institut d'Astrophysique Spatiale, CNRS/Universite Paris Sud, Batiment 121, 91405 Orsay, France. ; Finnish Meteorological Institute, Observation services, Erik Palmenin aukio 1, FI-00560 Helsinki, Finland. ; Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), CNRS/Universite d'Orleans, 45071 Orleans, France. ; Centre de Sciences Nucleaires et de Sciences de la Matiere, CNRS/IN2P3-Universite Paris Sud-UMR8609, Batiment 104, 91405 Orsay campus, France. ; Universitat der Bundeswehr, LRT-7, Werner Heisenberg Weg 39, 85577 Neubiberg, Germany. ; 1] Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), CNRS/Universite d'Orleans, 45071 Orleans, France [2] Laboratoire Interuniversitaire des Systemes Atmospheriques (LISA), UMR CNRS 7583, Universite Paris Est Creteil et Universite Paris Diderot, Institut Pierre Simon Laplace, 94000 Creteil, France. ; Laboratoire Interuniversitaire des Systemes Atmospheriques (LISA), UMR CNRS 7583, Universite Paris Est Creteil et Universite Paris Diderot, Institut Pierre Simon Laplace, 94000 Creteil, France. ; University of Turku, Department of Physics and Astronomy, Tuorla Observatory Vaisalantie 20, 21500 Piikkio, Finland. ; Center for Space and Habitability (CSH), University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland. ; Universite Grenoble Alpes/CNRS, Institut de Planetologie et d'Astrophysique de Grenoble, 414 Rue de la Piscine, Domaine Universitaire, 38000 Grenoble, France. ; Department of Chemistry, Materials and Surfaces, SP Technical Research Institute of Sweden, Box 857, 50115 Boras, Sweden. ; Institut fur Statistik und Wahrscheinlichkeitstheorie, Technische Universitat Wien, Wiedner Hauptstrasse 7, 1040 Wien, Austria.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25624103" target="_blank"〉PubMed〈/a〉
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
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Chemistry and Pharmacology
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Medicine
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Natural Sciences in General
,
Physics
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