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The Formation Mechanism of Gas Giants on Wide Orbits

Dodson-Robinson, Sarah E. and Veras, Dimitri and Ford, Eric B. and Beichman, C. A. (2009) The Formation Mechanism of Gas Giants on Wide Orbits. Astrophysical Journal, 707 (1). pp. 79-88. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20100108-204317511

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Abstract

The recent discoveries of massive planets on ultra-wide orbits of HR 8799 and Fomalhaut present a new challenge for planet formation theorists. Our goal is to figure out which of three giant planet formation mechanisms— core accretion (with or without migration), scattering from the inner disk, or gravitational instability—could be responsible for Fomalhaut b, HR 8799 b, c and d, and similar planets discovered in the future. This paper presents the results of numerical experiments comparing the long-period planet formation efficiency of each possible mechanism in model A star, G star, and M star disks. First, a simple core accretion simulation shows that planet cores forming beyond 35 AU cannot reach critical mass, even under the most favorable conditions one can construct. Second, a set of N-body simulations demonstrates that planet–planet scattering does not create stable, wide-orbit systems such as HR 8799. Finally, a linear stability analysis verifies previous work showing that global spiral instabilities naturally arise in high-mass disks. We conclude that massive gas giants on stable orbits with semimajor axes a ≳35 AU form by gravitational instability in the disk. We recommend that observers examine the planet detection rate as a function of stellar age, controlling for the planets’ dimming with time. Any age trend would indicate that planets on wide orbits are transient relics of scattering from the inner disk. If planet detection rate is found to be independent of stellar age, it would confirm our prediction that gravitational instability is the dominant mode of producing detectable planets on wide orbits.We also predict that the occurrence ratio of long-period to short-period gas giants should be highest for M dwarfs due to the inefficiency of core accretion and the expected small fragment mass (~10 M_(Jup)) in their disks.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/707/1/79DOIUNSPECIFIED
http://www.iop.org/EJ/abstract/0004-637X/707/1/79/PublisherUNSPECIFIED
ORCID:
AuthorORCID
Dodson-Robinson, Sarah E.0000-0002-8796-4974
Veras, Dimitri0000-0001-8014-6162
Ford, Eric B.0000-0001-6545-639X
Beichman, C. A.0000-0002-5627-5471
Additional Information:© 2009 The American Astronomical Society. Received 2009 July 29, accepted for publication 2009 October 19. Published 2009 November 18. Funding for S.D.R.’s work was provided by NASA through the Spitzer Space Telescope Fellowship Program. E.B.F. and D.V. received support from the National Science Foundation under the NSF grant listed below and the University of Florida under the auspices of U.F.’s High-Performance Computing Center. This project was the outgrowth of discussions at the 2009 Florida Astrophysics Winter Workshop which was supported by the University of Florida and the NSF grant listed below. The authors acknowledge valuable discussion among the workshop participants, particularly Ruth Murray-Clay, Kaitlin Kratter, Althea Moorhead, and Andrew Youdin. The authors also thank Aaron Boley, John Johnson, Christian Marois, Greg Laughlin, and Peter Bodenheimer for input on this work. The referee, Richard Durisen, provided particularly valuable insight into the current state of the gravitational instability subfield. This material is based upon work supported by the National Science Foundation under grant No. 0707203.
Funders:
Funding AgencyGrant Number
NASA Spitzer Space Science Telescope Fellowship ProgramUNSPECIFIED
NSF0707203
University of FloridaUNSPECIFIED
Subject Keywords:accretion, accretion disks; instabilities; planetary systems; planetary systems: formation; stars: formation
Issue or Number:1
Record Number:CaltechAUTHORS:20100108-204317511
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20100108-204317511
Official Citation:The Formation Mechanism of Gas Giants on Wide Orbits Sarah E. Dodson-Robinson, Dimitri Veras, Eric B. Ford, and C. A. Beichman 2009 ApJ 707 79-88 doi: 10.1088/0004-637X/707/1/79
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17125
Collection:CaltechAUTHORS
Deposited By: Joy Painter
Deposited On:11 Jan 2010 17:25
Last Modified:09 Mar 2020 13:19

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