Failed Stars and Super Planets A Report Based on the January 1998 Workshop on Substellar-Mass Objects (1998) / Chapter Skim
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4 Formation of SMOs
4 Formation of SMOs
Pages 35-43
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From page 35... ...
Continued growth of the solid core leads eventually to rapid buildup of the gaseous envelope and production of a planet comparable to or exceeding the mass of Jupiter. The difference between these two processes is potentially profound for at least one of the fundamental questions NASA seeks to address in its Origins program-the frequency witty which planetary systems grossly similar to ours occur elsewhere in the cosmos.
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From page 36... ...
Additional attempts to confirm this suggestion include plotting tile masses of detected SMOs against their orbital eccentricity, since the planetlike process should tend to produce objects in circular orbits (a consequence of the averaging out of the differing orbital angular momenta of the accreting planetesimals)
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From page 37... ...
FOR174~.\ OF917~ planet migrations is thus, po1en1iaDy, a key Actor in the Frequency of occurrence of terrestrial planets in extrasolar planetary systems 37
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From page 38... ...
The lower mass limit for brown dwarfs is unknown at present. The currently available mass distributions for SMOs is inadequate to quantitatively determine whether any particular segment of that population is over- or underabundant relative to its neighboring SMOs.
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From page 39... ...
The problem then quickly resolves itself to one of accretional infall by one or more compact objects from a surrounding envelope that generally has more than enough mass, even in highly clustered environments, to form a single brown dwarf. Brown dwarfs may still potentially occur by fragmentation out of the disk that no,,'~ally surrounds ~ growing protostar, but tendencies exist in the rotating infall process to equalize the two centers of attraction (normal star and brown dwarf)
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From page 40... ...
Of the remaining, possibilities for generating gaseous objects with masses intermediate between ordinary stars and planets, we argue that the mechanisms giving rise to brown dwarfs probably have more in common with star-formation processes than planet-formation processes. FORMATION OF BROWN DWARFS AND GIANT PLANETS Peter Bodenheimer University of California, Santa Cruz Recent observations have uncovered evidence for brown dwarfs in orbit around stars, in clusters, and in the general field.
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From page 41... ...
A number of issues remain to be resolved, including the survival of the companion, the fate of the fragments as influenced by the further accretion of gas and gravitational interactions between them, the effect of the numerical resolution of the calculations, and the effect of radiation transport, which was not included. Numerical calculations ofthe evolution of disks initially in equilibrium but subject to gravitational instability have been carried out by Greg Laughlin.'° A typical initial condition is a disk with a mass equal to that of the central star, a Gaussian surface-density profile, a pol~ropic equation of state, and a minimum Q value of about 1.3.
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From page 42... ...
For example, it appears that there is very little room between the giant planets' or between the terrestrials33 ~4 to squeeze in other planets that could survive the age of the solar system. Thus, the current planetary spacings may have resulted from a series of mergers and ejections resulting from dynamical instabilities occurring, as our system evolved to its current state.
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From page 43... ...
Studies ofthe dependence on the masses of the satellites of the dynamical lifetime of the inner Uranian satellites,'' equal-mass three-planet systems, and the four giant planets.~-, This set of simulations demonstrates interesting and as yet unexplained mass-scalin~ behaviour (especially for low-mass satellites)
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