889 research outputs found
Statistical Study of the Early Solar System's Instability with 4, 5 and 6 Giant Planets
Several properties of the Solar System, including the wide radial spacing and
orbital eccentricities of giant planets, can be explained if the early Solar
System evolved through a dynamical instability followed by migration of planets
in the planetesimal disk. Here we report the results of a statistical study, in
which we performed nearly 10^4 numerical simulations of planetary instability
starting from hundreds of different initial conditions. We found that the
dynamical evolution is typically too violent, if Jupiter and Saturn start in
the 3:2 resonance, leading to ejection of at least one ice giant from the Solar
System. Planet ejection can be avoided if the mass of the transplanetary disk
of planetesimals was large (M_disk>50 M_Earth), but we found that a massive
disk would lead to excessive dynamical damping (e.g., final e_55 < 0.01
compared to present e_55=0.044, where e_55 is the amplitude of the fifth
eccentric mode in the Jupiter's orbit), and to smooth migration that violates
constraints from the survival of the terrestrial planets. Better results were
obtained when the Solar System was assumed to have five giant planets initially
and one ice giant, with the mass comparable to that of Uranus and Neptune, was
ejected into interstellar space by Jupiter. The best results were obtained when
the ejected planet was placed into the external 3:2 or 4:3 resonance with
Saturn and M_disk ~ 20 M_Earth. The range of possible outcomes is rather broad
in this case, indicating that the present Solar System is neither a typical nor
expected result for a given initial state, and occurs, in best cases, with only
a ~5% probability (as defined by the success criteria described in the main
text). The case with six giant planets shows interesting dynamics but does
offer significant advantages relative to the five planet case.Comment: To appear in The Astronomical Journa
Fast Inversion Method for Determination of Planetary Parameters from Transit Timing Variations
The Transit Timing Variation (TTV) method relies on monitoring changes in
timing of transits of known exoplanets. Non-transiting planets in the system
can be inferred from TTVs by their gravitational interaction with the
transiting planet. The TTV method is sensitive to low-mass planets that cannot
be detected by other means. Here we describe a fast algorithm that can be used
to determine the mass and orbit of the non-transiting planets from the TTV
data. We apply our code, ttvim.f, to a wide variety of planetary systems to
test the uniqueness of the TTV inversion problem and its dependence on the
precision of TTV observations. We find that planetary parameters, including the
mass and mutual orbital inclination of planets, can be determined from the TTV
datasets that should become available in near future. Unlike the radial
velocity technique, the TTV method can therefore be used to characterize the
inclination distribution of multi-planet systems
Dynamics, Origin, and Activation of Main Belt Comets
The discovery of Main Belt Comets (MBCs) has raised many questions regarding
the origin and activation mechanism of these objects. Results of a study of the
dynamics of these bodies suggest that MBCs were formed in-situ as the remnants
of the break-up of large icy asteroids. Simulations show that similar to the
asteroids in the main belt, MBCs with orbital eccentricities smaller than 0.2
and inclinations lower than 25 degrees have stable orbits implying that many
MBCs with initially larger eccentricities and inclinations might have been
scattered to other regions of the asteroid belt. Among scattered MBCs,
approximately 20 percent reach the region of terrestrial planets where they
might have contributed to the accumulation of water on Earth. Simulations also
show that collisions among MBCs and small objects could have played an
important role in triggering the cometary activity of these bodies. Such
collisions might have exposed sub-surface water ice which sublimated and
created thin atmospheres and tails around MBCs. This paper discusses the
results of numerical studies of the dynamics of MBCs and their implications for
the origin of these objects. The results of a large numerical modeling of the
collisions of m-sized bodies with km-sized asteroids in the outer part of the
asteroid belt are also presented and the viability of the collision-triggering
activation scenario is discussed.Comment: 9 pages, 4 figures, to appear in the proceedings of IAU Symposium
263: Icy Bodies of the Solar System (Eds. D. Lazzaro, D. Prialnik, o. Schulz
and J.A. Fernandez), Cambridge Univ. Pres
A Region Void of Irregular Satellites Around Jupiter
An interesting feature of the giant planets of our solar system is the
existence of regions around these objects where no irregular satellites are
observed. Surveys have shown that, around Jupiter, such a region extends from
the outermost regular satellite Callisto, to the vicinity of Themisto, the
innermost irregular satellite. To understand the reason for the existence of
such a satellite-void region, we have studied the dynamical evolution of Jovian
irregulars by numerically integrating the orbits of several hundred test
particles, distributed in a region between 30 and 80 Jupiter-radii, for
different values of their semimajor axes, orbital eccentricities, and
inclinations. As expected, our simulations indicate that objects in or close to
the influence zones of the Galilean satellites become unstable because of
interactions with Ganymede and Callisto. However, these perturbations cannot
account for the lack of irregular satellites in the entire region between
Callisto and Themisto. It is suggested that at distances between 60 and 80
Jupiter-radii, Ganymede and Callisto may have long-term perturbative effects,
which may require the integrations to be extended to times much longer than 10
Myr. The interactions of irregular satellites with protosatellites of Jupiter
at the time of the formation of Jovian regulars may also be a destabilizing
mechanism in this region. We present the results of our numerical simulations
and discuss their applicability to similar satellite void-regions around other
giant planets.Comment: 21 pages, 9 figures, 2 tables, accepted for publication in the
Astronomical Journa
Binary YORP and Evolution of Binary Asteroids
The rotation states of kilometer sized near earth asteroids are known to be
affected by the YORP effect. In a related effect, Binary YORP (BYORP) the
orbital properties of a binary asteroid evolves under a radiation effect mostly
acting on a tidally locked secondary. The BYORP effect can alter the orbital
elements in years for a primary with a
secondary at . It can either separate the binary
components or cause them to collide. In this paper we devise a simple approach
to calculate the YORP effect on asteroids and BYORP effect on binaries
including effects due to primary oblateness and the sun. We apply this to
asteroids with known shapes as well as a set of randomly generated bodies with
various degrees of smoothness. We find a strong correlation between the
strengths of an asteroid's YORP and BYORP effects. Therefore, a statistical
knowledge on one, could be used to estimate the effect of the other. We show
that the action of BYORP preferentially shrinks rather than expands the binary
orbit and that YORP preferentially slows down asteroids. This conclusion holds
for the two extremes of thermal conductivities studied in this work and
assuming the asteroid reaches a stable point, but may break down for moderate
thermal conductivity. The YORP and BYORP effects are shown to be smaller than
what could be naively expected due to near cancellation of the effects on small
scales. Taking this near cancellation into account, a simple order of magnitude
estimate of the YORP and BYORP effects as function of the sizes and smoothness
of the bodies is calculated. Finally, we provide a simple proof showing that
there is no secular effect due to absorption of radiation in BYORP.Comment: Accepted to Astronomical Journa
- …