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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 |
Appears in Collections: | 3.02 Abstract in Atti di convegno |
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Pajola_DPS_47_Abstracts.pdf | Abstract | 143.52 kB | Adobe PDF | View/Open |
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