49 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
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
Dynamics of the giant planets of the solar system in the gaseous proto-planetary disk and relationship to the current orbital architecture
We study the orbital evolution of the 4 giant planets of our solar system in
a gas disk. Our investigation extends the previous works by Masset and
Snellgrove (2001) and Morbidelli and Crida (2007, MC07), which focussed on the
dynamics of the Jupiter-Saturn system. The only systems that we found to reach
a steady state are those in which the planets are locked in a quadruple mean
motion resonance (i.e. each planet is in resonance with its neighbor). In total
we found 6 such configurations. For the gas disk parameters found in MC07,
these configurations are characterized by a negligible migration rate. After
the disappearance of the gas, and in absence of planetesimals, only two of
these six configurations (the least compact ones) are stable for a time of
hundreds of millions of years or more. The others become unstable on a
timescale of a few My. Our preliminary simulations show that, when a
planetesimal disk is added beyond the orbit of the outermost planet, the
planets can evolve from the most stable of these configurations to their
current orbits in a fashion qualitatively similar to that described in Tsiganis
et al. (2005).Comment: The Astronomical Journal (17/07/2007) in pres
Origin of the Structure of the Kuiper Belt during a Dynamical Instability in the Orbits of Uranus and Neptune
We explore the origin and orbital evolution of the Kuiper belt in the
framework of a recent model of the dynamical evolution of the giant planets,
sometimes known as the Nice model. This model is characterized by a short, but
violent, instability phase, during which the planets were on large eccentricity
orbits. One characteristic of this model is that the proto-planetary disk must
have been truncated at roughly 30 to 35 AU so that Neptune would stop migrating
at its currently observed location. As a result, the Kuiper belt would have
initially been empty. In this paper we present a new dynamical mechanism which
can deliver objects from the region interior to ~35 AU to the Kuiper belt
without excessive inclination excitation. Assuming that the last encounter with
Uranus delivered Neptune onto a low-inclination orbit with a semi-major axis of
~27 AU and an eccentricity of ~0.3, and that subsequently Neptune's
eccentricity damped in ~1 My, our simulations reproduce the main observed
properties of the Kuiper belt at an unprecedented level
The Origin Of Asteroid 101955 (1999 Rq(36))
Near-Earth asteroid (NEA) 101955 (1999 RQ(36); henceforth RQ36) is especially accessible to spacecraft and is the primary target of NASA\u27s OSIRIS-REx sample return mission; it is also a potentially hazardous asteroid. We combine dynamical and spectral information to identify the most likely main-belt origin of RQ(36) and we conclude that it is the Polana family, located at a semimajor axis of about 2.42 AU. We also conclude that the Polana family may be the most important inner-belt source of low-albedo NEAs. These conclusions are based on the following results. (1) Dynamical evidence strongly favors an inner-belt, low-inclination (2.15 AU \u3c a \u3c 2.5 AU and i \u3c 10 degrees) origin, suggesting the v(6) resonance as the preferred (95% probability) delivery route. (2) This region is dominated by the Nysa and Polana families. (3) The Polana family is characterized by low albedos and B-class spectra or colors, the same albedo and spectral class as RQ36. (4) The Sloan Digital Sky Survey colors show that the Polana family is the branch of the Nysa-Polana complex that extends toward the v(6) resonance; furthermore, the Polana family has delivered objects of the size of RQ36 and larger into the v(6) resonance. (5) A quantitative comparison of visible and near-infrared spectra does not yield a unique match for RQ36; however, it is consistent with a compositional link between RQ36 and the Polana family
Libration-induced Orbit Period Variations Following the DART Impact
The Double Asteroid Redirection Test (DART) mission will be the first test of a kinetic impactor as a means of planetary defense. In late 2022, DART will collide with Dimorphos, the secondary in the Didymos binary asteroid system. The impact will cause a momentum transfer from the spacecraft to the binary asteroid, changing the orbit period of Dimorphos and forcing it to librate in its orbit. Owing to the coupled dynamics in binary asteroid systems, the orbit and libration state of Dimorphos are intertwined. Thus, as the secondary librates, it also experiences fluctuations in its orbit period. These variations in the orbit period are dependent on the magnitude of the impact perturbation, as well as the system鈥檚 state at impact and the moments of inertia of the secondary. In general, any binary asteroid system whose secondary is librating will have a nonconstant orbit period on account of the secondary鈥檚 fluctuating spin rate. The orbit period variations are typically driven by two modes: a long period and a short period, each with significant amplitudes on the order of tens of seconds to several minutes. The fluctuating orbit period offers both a challenge and an opportunity in the context of the DART mission. Orbit period oscillations will make determining the post-impact orbit period more difficult but can also provide information about the system鈥檚 libration state and the DART impact