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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 3 CONTRIBUTI IN ATTI DI CONVEGNO (Proceedings)
  4. 3.02 Abstract in Atti di convegno
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/26078
Title: The primordial nucleus of Comet 67P/Churyumov-Gerasimenko
Authors: Davidsson, Bjorn
Sierks, Holger
Guettler, Carsten
MARZARI, FRANCESCO
PAJOLA, MAURIZIO 
Rickman, Hans
A'Hearn, Michael
Auger, Anne-Therese
El-Maarry, Mohamed
FORNASIER, SONIA
Gutierrez, Pedro
Keller, Horst Uwe
MASSIRONI, MATTEO
Snodgrass, Colin
Vincent, Jean-Baptiste
Barbieri, Cesare
Lamy, Philippe
Rodrigo, Rafael
Koschny, Detlef
Barucci, Antonella
Bertaux, Jean-Loup
BERTINI, IVANO
CREMONESE, Gabriele 
Da Deppo, Vania
Debei, Stefano
De Cecco, Mariolino
Feller, Clement
FULLE, Marco 
Groussin, Olivier
Hviid, Stubbe
Hoefner, Sebastian
Ip, Wing-Huen
Jorda, Laurent
Knollenberg, Joerg
Kovacs, Gabor
Kramm, Joerg-Rainer
Kuehrt, Ekkehard
Kueppers, Michael
La Forgia, Fiorangela
Lara, Luisa
Lazzarin, Monica
Lopez Moreno, Jose
Moissl-Fraund, Richard
Mottola, Stefano
Naletto, Giampiero
Oklay, Nilda
Thomas, Nicolas
Tubiana, Cecilia
Issue Date: 2015
Volume: AAS/Division for Planetary Sciences Meeting Abstracts #47
First Page: 413.15
Abstract: Observations of Comet 67P/Churyumov-Gerasimenko by Rosetta show that the nucleus is bi-lobed, extensively layered, has a low bulk density, a high dust-to-ice mass ratio (implying high porosity), and weak strength except for a thin sintered surface layer. The comet is rich in supervolatiles (CO, CO2, N2), may contain amorphous water ice, and displays little to no signs of aqueous alteration. Lack of phyllosilicates in Stardust samples from Comet 81P/Wild 2 provides further support that comet nuclei did not contain liquid water.These properties differ from those expected for 50-200 km diameter bodies in the primordial disk. We find that thermal processing due to Al-26, combined with collisional compaction, creates a population of medium-sized bodies that are comparably dense, compacted, strong, heavily depleted in supervolatiles, containing little to no amorphous water ice, and that have experienced extensive aqueous alteration. Irregular satellites Phoebe and Himalia are potential representatives of this population. Collisional rubble piles inherit these properties from their parents. We therefore conclude that observed comet nuclei are primordial rubble piles, and not collisional rubble piles.We propose a concurrent comet and TNO formation scenario that is consistent with these observations. We argue that TNOs form due to streaming instabilities at sizes of about 50-400 km and that about 350 of these grow slowly in a low-mass primordial disk to the size of Triton, causing little viscous stirring during growth. We propose a dynamically cold primordial disk, that prevents medium-sized TNOs from breaking into collisional rubble piles, and allows for the survival of primordial rubble-pile comets. We argue that comets form by hierarchical agglomeration out of material that remains after TNO formation. This slow growth is necessary to avoid thermal processing by Al-26, and to allow comet nuclei to incorporate 3 Myr old material from the inner Solar System, found in Stardust samples. Growth in the Solar Nebula creates porous single-lobe nuclei, while continued growth in a mildly viscously stirred primordial disk creates denser outer layers, and allow bi-lobe nucleus formation through mergers.
Conference Name: 47th Annual Meeting for Division for Planetary Sciences
Conference Place: Washington, DC
Conference Date: 8– 3 November, 2015
URI: http://hdl.handle.net/20.500.12386/26078
URL: https://aas.org/meetings/dps47
Bibcode ADS: 2015DPS....4741315D
Fulltext: open
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