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Reassessing the formation of the inner Oort cloud in an embedded star cluster

Brasser, R. and Duncan, M. J. and Levison, H. F. and Schwamb, M. E. and Brown, M. E. (2012) Reassessing the formation of the inner Oort cloud in an embedded star cluster. Icarus, 217 (1). pp. 1-19. ISSN 0019-1035. doi:10.1016/j.icarus.2011.10.012.

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We re-examine the formation of the inner Oort comet cloud while the Sun was in its birth cluster with the aid of numerical simulations. This work is a continuation of an earlier study (Brasser, R., Duncan, M.J., Levison, H.F. [2006]. Icarus 184, 59–82) with several substantial modifications. First, the system consisting of stars, planets and comets is treated self-consistently in our N-body simulations, rather than approximating the stellar encounters with the outer Solar System as hyperbolic fly-bys. Second, we have included the expulsion of the cluster gas, a feature that was absent previously. Third, we have used several models for the initial conditions and density profile of the cluster – either a Hernquist or Plummer potential – and chose other parameters based on the latest observations of embedded clusters from the literature. These other parameters result in the stars being on radial orbits and the cluster collapses. Similar to previous studies, in our simulations the inner Oort cloud is formed from comets being scattered by Jupiter and Saturn and having their pericentres decoupled from the planets by perturbations from the cluster gas and other stars. We find that all inner Oort clouds formed in these clusters have an inner edge ranging from 100 AU to a few hundred AU, and an outer edge at over 100,000 AU, with little variation in these values for all clusters. All inner Oort clouds formed are consistent with the existence of (90377) Sedna, an inner Oort cloud dwarf planetoid, at the inner edge of the cloud: Sedna tends to be at the innermost 2% for Plummer models, while it is 5% for Hernquist models. We emphasise that the existence of Sedna is a generic outcome. We define a ‘concentration radius’ for the inner Oort cloud and find that its value increases with increasing number of stars in the cluster, ranging from 600 AU to 1500 AU for Hernquist clusters and from 1500 AU to 4000 AU for Plummer clusters. The increasing trend implies that small star clusters form more compact inner Oort clouds than large clusters. We are unable to constrain the number of stars that resided in the cluster since most clusters yield inner Oort clouds that could be compatible with the current structure of the outer Solar System. The typical formation efficiency of the inner Oort cloud is 1.5%, significantly lower than previous estimates. We attribute this to the more violent dynamics that the Sun experiences as it rushes through the centre of the cluster during the latter’s initial phase of violent relaxation.

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URLURL TypeDescription Paper
Brown, M. E.0000-0002-8255-0545
Additional Information:© 2011 Elsevier Inc. Received 29 July 2011; Revised 16 October 2011; Accepted 18 October 2011; Available online 28 October 2011. R.B. gratefully thanks Germany’s Helmholtz Alliance and their ‘Planetary Evolution and Life’ programme for financial support. M.J.D. acknowledges funding from Canada’s NSERC. H.F.L. gratefully acknowledges funding from NASA through their Origin of Solar Systems programme. MES and M.E.B. acknowledge receiving funding from NASA Origins of Solar Systems Program Grant NNG05GI02G. M.E.S. is supported by a NASA Earth and Space Science Fellowship and is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1003258.
Funding AgencyGrant Number
Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF)UNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
NASA Earth and Space Science FellowshipUNSPECIFIED
NSF Astronomy and Astrophysics FellowshipAST-1003258
Subject Keywords:Origin, Solar System; Comets, Dynamics; Planetary dynamics
Issue or Number:1
Record Number:CaltechAUTHORS:20120228-161254858
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Official Citation:R. Brasser, M.J. Duncan, H.F. Levison, M.E. Schwamb, M.E. Brown, Reassessing the formation of the inner Oort cloud in an embedded star cluster, Icarus, Volume 217, Issue 1, January 2012, Pages 1-19, ISSN 0019-1035, 10.1016/j.icarus.2011.10.012.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29511
Deposited On:29 Feb 2012 18:01
Last Modified:09 Nov 2021 17:07

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