1,649 research outputs found
Secular Effects of Tidal Damping in Compact Planetary Systems
We describe the long-term evolution of compact systems of terrestrial
planets, using a set of simulations that match the statistical properties of
the observed exoplanet distribution. The evolution is driven by tidal
dissipation in the planetary interiors, but the systems evolve as a whole due
to secular gravitational interactions. We find that, for Earth-like dissipation
levels, planetary orbits can be circularised out to periods of order 100 days,
an order of magnitude larger than is possible for single planets. The resulting
distribution of eccentricities is a qualitative match to that inferred from
transit timing variations, with a minority of non-zero eccentricities
maintained by particular secular configurations. The coupling of the tidal and
secular processes enhance the inward migration of the innermost planets in
these systems, and can drive them to short orbital periods. Resonant
interactions of both the mean motion and secular variety are observed, although
the interactions are not strong enough to drive systemic instability in most
cases. However, we demonstrate that these systems can easily be driven unstable
if coupled to giant planets on longer period orbits.Comment: 17 pages, 22 figures, 2 tables, submitted to Monthly Notices of the
Royal Astronomical Societ
Accounting for Multiplicity in Calculating Eta Earth
Using the updated exoplanet population parameters of our previous study,
which includes the planetary radius updates from Gaia DR2 and an inferred
multiplicity distribution, we provide a revised calculation.
This is achieved by sampling planets from our derived population model and
determining which planets meet our criterion for habitability. To ensure robust
results, we provide probabilities calculated over a range of upper radius
limits. Our most optimistic criterion for habitability provides an
value of . We also
consider the effects of multiplicity and the number of habitable planets each
system may contain. Our calculation indicates that of GK dwarfs
have more than one planet within their habitable zone. This optimistic
habitability criterion also suggests that of solar-like stars
will harbor 5 or more habitable planets. These tightly packed highly habitable
system should be extremely rare, but still possible. Even with our most
pessimistic criterion we still expect that of solar-like stars
harbor more than one habitable planet.Comment: 7 pages, 1 figure; Accepted for publication in MNRA
Changing Face of the Extrasolar Giant Planet, HD 209458b
High-resolution atmospheric flow simulations of the tidally-locked extrasolar
giant planet, HD 209458b, show large-scale spatio-temporal variability. This is
in contrast to the simple, permanent day/night (i.e., hot/cold) picture. The
planet's global circulation is characterized by a polar vortex in motion around
each pole and a banded structure corresponding to ~3 broad zonal (east-west)
jets. For very strong jets, the circulation-induced temperature difference
between moving hot and cold regions can reach up to ~1000 K, suggesting that
atmospheric variability could be observed in the planet's spectral and
photometric signatures.Comment: 6 pages, 1 ps figure, 2 low-res color figures (JPEG). Figure 3
updated. Contact authors for hi-res versions of color figures. Accepted for
publication in ApJ
Merger of Black Holes in the Galactic Center
We present the results of three body simulations focused on understanding the
fates of intermediate mass black holes (IBH) that drift within the central 0.5
pc of the Galaxy. In particular, we modeled the interactions between pairs of
black holes as they orbit a central blac k hole of mass
. The simulations performed assume a
Schwarzschild geometry and account for Chandrasekhar dynamical friction as well
as acceleration resulting from energy lost due to gravitational radiation.
We found the branching ratio for one of the orbiting IBHs to merge with the
CBH was 0.95 and is independent of the inner IBH's initial eccentricity as well
as the rate of sinking. This, coupled with an infall rate of yrs
for an IBH to drift into the Galactic center, results in an IBH-CBH merger
every Myrs. Lastly we found that the IBH-IBH-CBH triple body
system ``resets'' itself, in the sense that a system with an inner I BH with an
initially circular orbit generally left behind an IBH with a large
eccentricity, whereas a system in which the inner IBH had a high eccentricity
() usually left a remnant with low eccentricity. Branching ratios
for different outcomes are also similar in the two cases.Comment: Official paper to appear in November 2008 issue of Ap
Close-in giant-planet formation via in-situ gas accretion and their natal disk properties
The origin of close-in Jovian planets is still elusive. We examine the
in-situ gas accretion scenario as a formation mechanism of these planets. We
reconstruct natal disk properties from the occurrence rate distribution of
close-in giant planets, under the assumption that the occurrence rate may
reflect the gas accretion efficiency onto cores of these planets. We find that
the resulting gas surface density profile becomes an increasing function of the
distance from the central star with some structure at au. This
profile is quite different from the standard minimum-mass solar nebula model,
while our profile leads to better reproduction of the population of observed
close-in super-Earths based on previous studies. We compute the resulting
magnetic field profiles and find that our profiles can be fitted by stellar
dipole fields () in the vicinity of the central star and
large-scale fields () at the inner disk regions, either if the
isothermal assumption breaks down or if nonideal MHD effects become important.
For both cases, the transition between these two profiles occurs at au, which corresponds to the period valley of giant exoplanets. Our work
provides an opportunity to test the in-situ gas accretion scenario against disk
quantities, which may constrain the gas distribution of the minimum-mass {\it
extra}solar nebula.Comment: 5 pages, 3 figures, accepted for publication in A&A Letter
- …