154 research outputs found
Dynamical Friction and Resonance Trapping in Planetary Systems
A restricted planar circular three-body system, consisting of the Sun and two
planets, is studied as a simple model for a planetary system. The mass of the
inner planet is considered to be larger and the system is assumed to be moving
in a uniform interplanetary medium with constant density. Numerical
integrations of this system indicate a resonance capture when the dynamical
friction of the interplanetary medium is taken into account. As a result of
this resonance trapping, the ratio of orbital periods of the two planets
becomes nearly commensurate and the eccentricity and semimajor axis of the
orbit of the outer planet and also its angular momentum and total energy become
constant. It appears from the numerical work that the resulting
commensurability and also the resonant values of the orbital elements of the
outer planet are essentially independent of the initial relative positions of
the two bodies. The results of numerical integrations of this system are
presented and the first-order partially averaged equations are studied in order
to elucidate the behavior of the system while captured in resonance.Comment: plainTeX, 30 pages, 18 graphs, accepted by MNRA
The Stability and Prospects of the Detection of Terrestrial/Habitable Planets in Multiplanet and Multiple Star Systems
Given the tendency of planets to form in multiples, and the observational
evidence in support of the existence of potential planet-hosting stars in
binaries or clusters, it is expected that extrasolar terrestrial planes are
more likely to be found in multiple body systems. This paper discusses the
prospects of the detection of terrestrial/habitable planets in multibody
systems by presenting the results of a study of the long-term stability of
these objects in systems with multiple giant planets (particularly those in
eccentric and/or in mean-motion resonant orbits), systems with close-in
Jupiter-like bodies, and systems of binary stars. The results of simulations
show that while short-period terrestrial-class objects that are captured in
near mean-motion resonances with migrating giant planets are potentially
detectable via transit photometry or the measurement of the variations of the
transit-timing due to their close-in Jovian-mass planetary companions, the
prospect of the detection of habitable planets with radial velocity technique
is higher in systems with multiple giant planets outside the habitable zone and
binary systems with moderately separated stellar companions.Comment: 9 pages, 5 figures, to appear in the proceedings of the conference
"Extrasolar planets in multi-body systems: theory and observations" (August
2008, Torun, Poland
Probing the effect of gravitational microlensing on the measurements of the Rossiter-McLaughlin effect
In general, in the studies of transit light-curves and the
Rossiter-McLaughlin (RM), the contribution of the planet's gravitational
microlensing is neglected. Theoretical studies, have, however shown that the
planet's microlensing can affect the transit light-curve and in some extreme
cases cause the transit depth to vanish. In this letter, we present the results
of our quantitative analysis of microlening on the RM effect. Results indicate
that for massive planets in on long period orbits, the planet's microlensing
will have considerable contribution to the star's RV measurements. We present
the details of our study, and discuss our analysis and results.Comment: 6 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
Terrestrial Planet Formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars
Models of terrestrial planet formation for our solar system have been
successful in producing planets with masses and orbits similar to those of
Venus and Earth. However, these models have generally failed to produce
Mars-sized objects around 1.5 AU. The body that is usually formed around Mars'
semimajor axis is, in general, much more massive than Mars. Only when Jupiter
and Saturn are assumed to have initially very eccentric orbits (e 0.1),
which seems fairly unlikely for the solar system, or alternately, if the
protoplanetary disk is truncated at 1.0 AU, simulations have been able to
produce Mars-like bodies in the correct location. In this paper, we examine an
alternative scenario for the formation of Mars in which a local depletion in
the density of the protosolar nebula results in a non-uniform formation of
planetary embryos and ultimately the formation of Mars-sized planets around 1.5
AU. We have carried out extensive numerical simulations of the formation of
terrestrial planets in such a disk for different scales of the local density
depletion, and for different orbital configurations of the giant planets. Our
simulations point to the possibility of the formation of Mars-sized bodies
around 1.5 AU, specifically when the scale of the disk local mass-depletion is
moderately high (50-75%) and Jupiter and Saturn are initially in their current
orbits. In these systems, Mars-analogs are formed from the protoplanetary
materials that originate in the regions of disk interior or exterior to the
local mass-depletion. Results also indicate that Earth-sized planets can form
around 1 AU with a substantial amount of water accreted via primitive
water-rich planetesimals and planetary embryos. We present the results of our
study and discuss their implications for the formation of terrestrial planets
in our solar system.Comment: Accepted for publication in The Astrophysical Journa
A Compound model for the origin of Earth's water
One of the most important subjects of debate in the formation of the solar
system is the origin of Earth's water. Comets have long been considered as the
most likely source of the delivery of water to Earth. However, elemental and
isotopic arguments suggest a very small contribution from these objects. Other
sources have also been proposed, among which, local adsorption of water vapor
onto dust grains in the primordial nebula and delivery through planetesimals
and planetary embryos have become more prominent. However, no sole source of
water provides a satisfactory explanation for Earth's water as a whole. In view
of that, using numerical simulations, we have developed a compound model
incorporating both the principal endogenous and exogenous theories, and
investigating their implications for terrestrial planet formation and
water-delivery. Comets are also considered in the final analysis, as it is
likely that at least some of Earth's water has cometary origin. We analyze our
results comparing two different water distribution models, and complement our
study using D/H ratio, finding possible relative contributions from each
source, focusing on planets formed in the habitable zone. We find that the
compound model play an important role by showing more advantage in the amount
and time of water-delivery in Earth-like planets.Comment: Accepted for publication in The Astrophysical Journa
SOAP-T: A tool to study the light-curve and radial velocity of a system with a transiting planet and a rotating spotted star
We present an improved version of SOAP (Boisse et al. 2012) named "SOAP-T",
which can generate the radial velocity variations and light-curves for systems
consisting of a rotating spotted star with a transiting planet. This tool can
be used to study the anomalies inside transit light-curves and the
Rossiter-McLaughlin effect, to better constrain the orbital configuration and
properties of planetary systems and active zones of their host stars. Tests of
the code are presented to illustrate its performance and to validate its
capability when compared with analytical models and real data. Finally, we
apply SOAP-T to the active star, HAT-P-11, observed by the NASA Kepler space
telescope and use this system to discuss the capability of this tool in
analyzing light-curves for the cases where the transiting planet overlaps with
the star's spots.Comment: 9 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Dynamics of Planetesimals due to Gas Drag from an Eccentric Precessing Disk
We analyze the dynamics of individual kilometer-size planetesimals in
circumstellar orbits of a tight binary system. We include both the
gravitational perturbations of the secondary star and a non-linear gas drag
stemming from an eccentric gas disk with a finite precession rate. We consider
several precession rates and eccentricities for the gas, and compare the
results with a static disk in circular orbit.
The disk precession introduces three main differences with respect to the
classical static case: (i) The equilibrium secular solutions generated by the
gas drag are no longer fixed points in the averaged system, but limit cycles
with frequency equal to the precession rate of the gas. The amplitude of the
cycle is inversely dependent on the body size, reaching negligible values for
km size planetesimals. (ii) The maximum final eccentricity attainable
by small bodies is restricted to the interval between the gas eccentricity and
the forced eccentricity, and apsidal alignment is no longer guaranteed for
planetesimals strongly coupled with the gas. (iii) The characteristic
timescales of orbital decay and secular evolution decrease significantly with
increasing precession rates, with values up to two orders of magnitude smaller
than for static disks.
Finally, we apply this analysis to the -Cephei system and estimate
impact velocities for different size bodies and values of the gas eccentricity.
For high disk eccentricities, we find that the disk precession decreases the
velocity dispersion between different size planetesimals, thus contributing to
accretional collisions in the outer parts of the disk. The opposite occurs for
almost circular gas disks, where precession generates an increase in the
relative velocities.Comment: 11 pages, 9 figures. Accepted in MNRA
Super-Earths: A New Class of Planetary Bodies
Super-Earths, a class of planetary bodies with masses ranging from a few
Earth-masses to slightly smaller than Uranus, have recently found a special
place in the exoplanetary science. Being slightly larger than a typical
terrestrial planet, super-Earths may have physical and dynamical
characteristics similar to those of Earth whereas unlike terrestrial planets,
they are relatively easier to detect. Because of their sizes, super-Earths can
maintain moderate atmospheres and possibly dynamic interiors with plate
tectonics. They also seem to be more common around low-mass stars where the
habitable zone is in closer distances. This article presents a review of the
current state of research on super-Earths, and discusses the models of the
formation, dynamical evolution, and possible habitability of these objects.
Given the recent advances in detection techniques, the detectability of
super-Earths is also discussed, and a review of the prospects of their
detection in the habitable zones of low-mass stars is presented.Comment: A (non-technical) review of the literature on the current state
ofresearch on super-Earths. The topics include observation, formation,
dynamical evolution, habitability, composition, interior dynamics, magnetic
field, atmosphere, and propsect of detection. The article has 44 pages, 27
figures, and 203 references. It has been accepted for publication in the
journal Contemporary Physics (2011
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