394 research outputs found
Formation and Evolution of Planetary Systems in Presence of Highly Inclined Stellar Perturbers
The presence of highly eccentric extrasolar planets in binary stellar systems
suggests that the Kozai effect has played an important role in shaping their
dynamical architectures. However, the formation of planets in inclined binary
systems poses a considerable theoretical challenge, as orbital excitation due
to the Kozai resonance implies destructive, high-velocity collisions among
planetesimals. To resolve the apparent difficulties posed by Kozai resonance,
we seek to identify the primary physical processes responsible for inhibiting
the action of Kozai cycles in protoplanetary disks. Subsequently, we seek to
understand how newly-formed planetary systems transition to their observed,
Kozai-dominated dynamical states. We find that theoretical difficulties in
planet formation arising from the presence of a distant companion star, posed
by the Kozai effect and other secular perturbations, can be overcome by a
proper account of gravitational interactions within the protoplanetary disk. In
particular, fast apsidal recession induced by disk self-gravity tends to erase
the Kozai effect, and ensure that the disk's unwarped, rigid structure is
maintained. Subsequently, once a planetary system has formed, the Kozai effect
can continue to be wiped out as a result of apsidal precession, arising from
planet-planet interactions. However, if such a system undergoes a dynamical
instability, its architecture may change in such a way that the Kozai effect
becomes operative. The results presented here suggest that planetary formation
in highly inclined binary systems is not stalled by perturbations, arising from
the stellar companion. Consequently, planet formation in binary stars is
probably no different from that around single stars on a qualitative level.
Furthermore, it is likely that systems where the Kozai effect operates,
underwent a transient phase of dynamical instability in the past.Comment: 9 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Inclined asymmetric librations in exterior resonances
Librational motion in celestial mechanics is generally associated with the
existence of stable resonant configurations and signified by the existence of
stable periodic solutions and oscillation of critical (resonant) angles. When
such an oscillation takes place around a value different than 0 or , the
libration is called asymmetric. In the context of the planar circular
restricted three-body problem (CRTBP), asymmetric librations have been
identified for the exterior mean-motion resonances (MMRs) 1:2, 1:3 etc. as well
as for co-orbital motion (1:1). In exterior MMRs the massless body is the outer
one. In this paper, we study asymmetric librations in the 3-dimensional space.
We employ the computational approach of Markellos (1978) and compute families
of asymmetric periodic orbits and their stability. Stable, asymmetric periodic
orbits are surrounded in phase space by domains of initial conditions which
correspond to stable evolution and librating resonant angles. Our computations
were focused on the spatial circular restricted three-body model of the
Sun-Neptune-TNO system (TNO= trans-Neptunian object). We compare our results
with numerical integrations of observed TNOs, which reveal that some of them
perform 1:2-resonant, inclined asymmetric librations. For the stable 1:2 TNOs
librators, we find that their libration seems to be related with the vertically
stable planar asymmetric orbits of our model, rather than the 3-dimensional
ones found in the present study.Comment: Accepted for publication in CeMD
Vertical instability and inclination excitation during planetary migration
We consider a two-planet system, which migrates under the influence of
dissipative forces that mimic the effects of gas-driven (Type II) migration. It
has been shown that, in the planar case, migration leads to resonant capture
after an evolution that forces the system to follow families of periodic
orbits. Starting with planets that differ slightly from a coplanar
configuration, capture can, also, occur and, additionally, excitation of
planetary inclinations has been observed in some cases. We show that excitation
of inclinations occurs, when the planar families of periodic orbits, which are
followed during the initial stages of planetary migration, become vertically
unstable. At these points, {\em vertical critical orbits} may give rise to
generating stable families of periodic orbits, which drive the evolution
of the migrating planets to non-coplanar motion. We have computed and present
here the vertical critical orbits of the and resonances, for
various values of the planetary mass ratio. Moreover, we determine the limiting
values of eccentricity for which the "inclination resonance" occurs.Comment: Accepted for publication in Celestial Mechanics and Dynamical
Astronom
Reconstructing the size distribution of the primordial Main Belt
In this work we aim to constrain the slope of the size distribution of
main-belt asteroids, at their primordial state. To do so we turn out attention
to the part of the main asteroid belt between 2.82 and 2.96~AU, the so-called
"pristine zone", which has a low number density of asteroids and few, well
separated asteroid families. Exploiting these unique characteristics, and using
a modified version of the hierarchical clustering method we are able to remove
the majority of asteroid family members from the region. The remaining,
background asteroids should be of primordial origin, as the strong 5/2 and 7/3
mean-motion resonances with Jupiter inhibit transfer of asteroids to and from
the neighboring regions. The size-frequency distribution of asteroids in the
size range has a slope . Using Monte-Carlo
methods, we are able to simulate, and compensate for the collisional and
dynamical evolution of the asteroid population, and get an upper bound for its
size distribution slope . In addition, applying the same 'family
extraction' method to the neighboring regions, i.e. the middle and outer belts,
and comparing the size distributions of the respective background populations,
we find statistical evidence that no large asteroid families of primordial
origin had formed in the middle or pristine zones
Medium Earth Orbit dynamical survey and its use in passive debris removal
The Medium Earth Orbit (MEO) region hosts satellites for navigation,
communication, and geodetic/space environmental science, among which are the
Global Navigation Satellites Systems (GNSS). Safe and efficient removal of
debris from MEO is problematic due to the high cost for maneuvers needed to
directly reach the Earth (reentry orbits) and the relatively crowded GNSS
neighborhood (graveyard orbits). Recent studies have highlighted the
complicated secular dynamics in the MEO region, but also the possibility of
exploiting these dynamics, for designing removal strategies. In this paper, we
present our numerical exploration of the long-term dynamics in MEO, performed
with the purpose of unveiling the set of reentry and graveyard solutions that
could be reached with maneuvers of reasonable DV cost. We simulated the
dynamics over 120-200 years for an extended grid of millions of fictitious MEO
satellites that covered all inclinations from 0 to 90deg, using non-averaged
equations of motion and a suitable dynamical model that accounted for the
principal geopotential terms, 3rd-body perturbations and solar radiation
pressure (SRP). We found a sizeable set of usable solutions with reentry times
that exceed ~40years, mainly around three specific inclination values: 46deg,
56deg, and 68deg; a result compatible with our understanding of MEO secular
dynamics. For DV <= 300 m/s (i.e., achieved if you start from a typical GNSS
orbit and target a disposal orbit with e<0.3), reentry times from GNSS
altitudes exceed ~70 years, while low-cost (DV ~= 5-35 m/s) graveyard orbits,
stable for at lest 200 years, are found for eccentricities up to e~0.018. This
investigation was carried out in the framework of the EC-funded "ReDSHIFT"
project.Comment: 39 pages, 23 figure
Constructing the secular architecture of the solar system I: The giant planets
Using numerical simulations, we show that smooth migration of the giant
planets through a planetesimal disk leads to an orbital architecture that is
inconsistent with the current one: the resulting eccentricities and
inclinations of their orbits are too small. The crossing of mutual mean motion
resonances by the planets would excite their orbital eccentricities but not
their orbital inclinations. Moreover, the amplitudes of the eigenmodes
characterising the current secular evolution of the eccentricities of Jupiter
and Saturn would not be reproduced correctly; only one eigenmode is excited by
resonance-crossing. We show that, at the very least, encounters between Saturn
and one of the ice giants (Uranus or Neptune) need to have occurred, in order
to reproduce the current secular properties of the giant planets, in particular
the amplitude of the two strongest eigenmodes in the eccentricities of Jupiter
and Saturn.Comment: Astronomy & Astrophysics (2009) in pres
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