The primordial nucleus of Comet 67P/Churyumov-Gerasimenko
Björn Davidsson
(1)
,
Holger Sierks
(2)
,
Carsten Guettler
(2)
,
Francesco Marzari
(3)
,
Maurizio Pajola
(4)
,
Hans Rickman
(5)
,
Michael A'Hearn
(6)
,
Anne-Therese Auger
(7)
,
Mohamed El-Maarry
(8)
,
Sonia Fornasier
(9)
,
Pedro J. Gutiérrez
(10)
,
Horst U. Keller
(11)
,
Matteo Massironi
(12)
,
Colin Snodgrass
(13)
,
Jean-Baptiste Vincent
(2)
,
Cesare Barbieri
(3)
,
Philippe Lamy
(7)
,
Rafael Rodrigo
(14)
,
Detlef Koschny
(15)
,
Antonella Barucci
(9)
,
Jean-Loup Bertaux
(16)
,
Ivano Bertini
(4)
,
Gabriele Cremonese
(17)
,
Vania da Deppo
(18)
,
Stefano Debei
(19)
,
Mariolino de Cecco
(20)
,
Clement Feller
(21)
,
Marco Fulle
(22)
,
Olivier Groussin
(7)
,
Stubbe Hviid
(23)
,
Sebastian Hoefner
(2)
,
Wing-Huen Ip
(24)
,
Laurent Jorda
(7)
,
Joerg Knollenberg
(23)
,
Gabor Kovacs
(2)
,
Joerg-Rainer Kramm
(2)
,
Ekkehard Kuehrt
(23)
,
Michael Kueppers
(25)
,
Fiorangela La Forgia
(3)
,
Luisa Lara
(10)
,
Monica Lazzarin
(3)
,
Jose Lopez-Moreno
(10)
,
Richard Moissl-Fraund
(25)
,
Stefano Mottola
(23)
,
Giampiero Naletto
(26)
,
Nilda Oklay
(2)
,
Nicolas Thomas
(8)
,
Cecilia Tubiana
(2)
1
Department of Physics and Astronomy [Uppsala]
2 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
3 Dipartimento di Fisica e Astronomia "Galileo Galilei"
4 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
5 CBK - Space Research Centre of Polish Academy of Sciences
6 Department of Astronomy [College Park]
7 LAM - Laboratoire d'Astrophysique de Marseille
8 Physikalisches Institut [Bern]
9 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
10 IAA - Instituto de Astrofísica de Andalucía
11 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
12 Dipartimento di Geoscienze [Padova]
13 School of Physical Sciences [Milton Keynes]
14 CAB - Centro de Astrobiologia [Madrid]
15 RSSD - Research and Scientific Support Department, ESTEC
16 PLANETO - LATMOS
17 OAPD - INAF - Osservatorio Astronomico di Padova
18 IFN - CNR Institute for Photonics and Nanotechnologies
19 UNITN - Università degli Studi di Trento = University of Trento
20 Department of Industrial Engineering [Padova]
21 UPD7 - Université Paris Diderot - Paris 7
22 OAT - INAF - Osservatorio Astronomico di Trieste
23 DLR Institute of Planetary Research
24 IANCU - Institute of Astronomy [Taiwan]
25 Operations Department (ESAC)
26 DEI - Department of Information Engineering [Padova]
2 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
3 Dipartimento di Fisica e Astronomia "Galileo Galilei"
4 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
5 CBK - Space Research Centre of Polish Academy of Sciences
6 Department of Astronomy [College Park]
7 LAM - Laboratoire d'Astrophysique de Marseille
8 Physikalisches Institut [Bern]
9 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
10 IAA - Instituto de Astrofísica de Andalucía
11 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
12 Dipartimento di Geoscienze [Padova]
13 School of Physical Sciences [Milton Keynes]
14 CAB - Centro de Astrobiologia [Madrid]
15 RSSD - Research and Scientific Support Department, ESTEC
16 PLANETO - LATMOS
17 OAPD - INAF - Osservatorio Astronomico di Padova
18 IFN - CNR Institute for Photonics and Nanotechnologies
19 UNITN - Università degli Studi di Trento = University of Trento
20 Department of Industrial Engineering [Padova]
21 UPD7 - Université Paris Diderot - Paris 7
22 OAT - INAF - Osservatorio Astronomico di Trieste
23 DLR Institute of Planetary Research
24 IANCU - Institute of Astronomy [Taiwan]
25 Operations Department (ESAC)
26 DEI - Department of Information Engineering [Padova]
Maurizio Pajola
- Fonction : Auteur
- PersonId : 767226
- ORCID : 0000-0002-3144-1277
Colin Snodgrass
- Fonction : Auteur
- PersonId : 759859
- ORCID : 0000-0001-9328-2905
- IdRef : 202450821
Cesare Barbieri
- Fonction : Auteur
- PersonId : 757032
- ORCID : 0000-0002-6257-9076
Vania da Deppo
- Fonction : Auteur
- PersonId : 763247
- ORCID : 0000-0001-6273-8738
Wing-Huen Ip
- Fonction : Auteur
- PersonId : 770404
- ORCID : 0000-0001-5368-386X
Laurent Jorda
- Fonction : Auteur
- PersonId : 746464
- IdHAL : laurent-jorda
- ORCID : 0000-0001-8735-3308
- IdRef : 180975161
Giampiero Naletto
- Fonction : Auteur
- PersonId : 773093
- ORCID : 0000-0003-2007-3138
Nicolas Thomas
- Fonction : Auteur
- PersonId : 757031
- ORCID : 0000-0002-0146-0071
Résumé
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.