Title:
Falling Evaporating Bodies as a Clue to Outline the Structure of the β
Pictoris Young Planetary
System
Authors:
Beust, Hervé; Morbidelli, Alessandro
Affiliation:
AA(Laboratoire d'Astrophysique, Observatoire de Grenoble, Grenoble Cedex
9, France),
AB(Observatoire de la Côte d'Azur, Nice Cedex 4, France)
Journal:
Icarus, Volume 143, Issue Icarus, pp. 170-188. (Icarus Homepage)
Publication Date:
01/2000
Origin:
ICAR
Abstract Copyright:
(c) 2000: Academic Press
Bibliographic Code:
2000Icar..143..170B
Abstract
Transient redshifted events monitored in the spectrum of β
Pictoris have been interpreted for many years as resulting from
the evaporation of numerous comet-like bodies in the vicinity of this
stars. This motivated the investigation of dynamical
mechanisms responsible for the origin of these star-grazing comets.
Among various ideas, a model involving mean-motion
resonances with a jovian-like planet was proposed a few years ago and
applied to the β Pictoris case (H. Beust and A.
Morbidelli 1996 Icarus 120, 358-370). According to this model, the
4:1 and possibly the 3:1 mean-motion resonances are able to
generate numerous star-grazers from an initially dynamically cold disk
of planetesimals. In this paper, detailed numerical
simulations of this dynamical process over a large number of particles
are presented, showing in particular that the model is robust
toward the presence of additional planets around the star. The question
of the evaporation rate of the comet-like bodies is also
investigated, showing that, in order to explain the observed spectral
events, the comet-like bodies should be larger than 10-20 km,
rather than 1 km as previously conjectured. This in turn makes it possible
to estimate the typical density of the planetesimal disk
required to explain the observed spectral phenomena, i.e., ~108 bodies
per astronomic unit in the resonance at 4 AU from the star.
Apart from the main redshifted spectral events, a few blueshifted events
were observed over the past few years. These spectral
events are clearly distinct from the main redshifted ones and cannot
be considered as outliers, although they are far less numerous.
In the simple framework of the mean-motion resonance model, these events,
which should correspond to bodies moving on
differently oriented orbits, should not be expected. We show that assuming
the presence of a terrestrial-like planet, well inside the
orbit of the jovian planet, may generate these additional events. Close
encounters with a terrestrial planet may extract some
particles from the resonance, and bring some of them to star-grazing
orbits, but with a different orbital orientation, so that they
generate blueshifted events.
The question of the refilling of the resonance is investigated. Two
basic models may be invoked: First, collisions among
planetesimals may replenish the resonance. This appears to be possible,
but the mass density of the planetesimal disk in the vicinity
of the resonance needs to be ~10 M⊕ per astronomic unit or
more, which is hardly realistic. Planetary migration may be a
second possible mechanism. A migrating resonance can capture new bodies
as it sweeps the disk. We show that this model is
realistic only if the migration velocity is high enough, i.e., compatible
with models invoking a tidal interaction with the disk, but
the reality of this mechanism in the β Pictoris disk must
be questioned.