481 research outputs found
The formation and habitability of terrestrial planets in the presence of hot jupiters
`Hot jupiters,' giant planets with orbits very close to their parent stars,
are thought to form farther away and migrate inward via interactions with a
massive gas disk. If a giant planet forms and migrates quickly, the
planetesimal population has time to re-generate in the lifetime of the disk and
terrestrial planets may form (Armitage 2003). We present results of simulations
of terrestrial planet formation in the presence of hot jupiters, broadly
defined as having orbital radii <= 0.5 AU. We show that terrestrial planets
similar to those in the Solar System can form around stars with hot jupiters,
and can have water contents equal to or higher than the Earth's. For small
orbital radii of hot jupiters (e.g. 0.15, 0.25 AU) potentially habitable
planets can form, but for semi-major axes of 0.5 AU or greater their formation
is suppressed. We show that the presence of an outer giant planet such as
Jupiter does not enhance the water content of the terrestrial planets, but
rather decreases their formation and water delivery timescales. We speculate
that asteroid belts may exist interior to the terrestrial planets in systems
with hot jupiters.Comment: 5 pages, 2 color figures in emulate ApJ style submitted to Icaru
Planet-planet scattering in planetesimal disks
We study the final architecture of planetary systems that evolve under the
combined effects of planet-planet and planetesimal scattering. Using N-body
simulations we investigate the dynamics of marginally unstable systems of gas
and ice giants both in isolation and when the planets form interior to a
planetesimal belt. The unstable isolated systems evolve under planet-planet
scattering to yield an eccentricity distribution that matches that observed for
extrasolar planets. When planetesimals are included the outcome depends upon
the total mass of the planets. For system masses exceeding about one Jupiter
mass the final eccentricity distribution remains broad, whereas for lower mass
planetary systems a combination of divergent orbital evolution and
recircularization of scattered planets results in a preponderance of nearly
circular final orbits. We also study the fate of marginally stable multiple
planet systems in the presence of planetesimal disks, and find that for high
planet masses the majority of such systems evolve into resonance. A significant
fraction lead to resonant chains that are planetary analogs of Jupiter's
Galilean satellites. We predict that a transition from eccentric to
near-circular orbits will be observed once extrasolar planet surveys detect
sub-Jovian mass planets at orbital radii of 5-10 AU.Comment: ApJ Letters, in pres
A New Hybrid N-Body-Coagulation Code for the Formation of Gas Giant Planets
We describe an updated version of our hybrid N-body-coagulation code for
planet formation. In addition to the features of our 2006-2008 code, our
treatment now includes algorithms for the 1D evolution of the viscous disk, the
accretion of small particles in planetary atmospheres, gas accretion onto
massive cores, and the response of N-bodies to the gravitational potential of
the gaseous disk and the swarm of planetesimals. To validate the N-body portion
of the algorithm, we use a battery of tests in planetary dynamics. As a first
application of the complete code, we consider the evolution of Pluto-mass
planetesimals in a swarm of 0.1-1 cm pebbles. In a typical evolution time of
1-3 Myr, our calculations transform 0.01-0.1 solar mass disks of gas and dust
into planetary systems containing super-Earths, Saturns, and Jupiters. Low mass
planets form more often than massive planets; disks with smaller alpha form
more massive planets than disks with larger alpha. For Jupiter-mass planets,
masses of solid cores are 10-100 Earth masses.Comment: revised version; 52 pages, 1 table, 19 figures; accepted in Ap
Formation of Super-Earths
Super-Earths are the most abundant planets known to date and are
characterized by having sizes between that of Earth and Neptune, typical
orbital periods of less than 100 days and gaseous envelopes that are often
massive enough to significantly contribute to the planet's overall radius.
Furthermore, super-Earths regularly appear in tightly-packed multiple-planet
systems, but resonant configurations in such systems are rare. This chapters
summarizes current super-Earth formation theories. It starts from the formation
of rocky cores and subsequent accretion of gaseous envelopes. We follow the
thermal evolution of newly formed super-Earths and discuss their atmospheric
mass loss due to disk dispersal, photoevaporation, core-cooling and collisions.
We conclude with a comparison of observations and theoretical predictions,
highlighting that even super-Earths that appear as barren rocky cores today
likely formed with primordial hydrogen and helium envelopes and discuss some
paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of
Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio
Belmonte and Hans Deeg, Ed
Earth and Terrestrial Planet Formation
The growth and composition of Earth is a direct consequence of planet
formation throughout the Solar System. We discuss the known history of the
Solar System, the proposed stages of growth and how the early stages of planet
formation may be dominated by pebble growth processes. Pebbles are small bodies
whose strong interactions with the nebula gas lead to remarkable new accretion
mechanisms for the formation of planetesimals and the growth of planetary
embryos.
Many of the popular models for the later stages of planet formation are
presented. The classical models with the giant planets on fixed orbits are not
consistent with the known history of the Solar System, fail to create a high
Earth/Mars mass ratio, and, in many cases, are also internally inconsistent.
The successful Grand Tack model creates a small Mars, a wet Earth, a realistic
asteroid belt and the mass-orbit structure of the terrestrial planets.
In the Grand Tack scenario, growth curves for Earth most closely match a
Weibull model. The feeding zones, which determine the compositions of Earth and
Venus follow a particular pattern determined by Jupiter, while the feeding
zones of Mars and Theia, the last giant impactor on Earth, appear to randomly
sample the terrestrial disk. The late accreted mass samples the disk nearly
evenly.Comment: Accepted for publication in Early Earth an AGU Monograph edited by
James Badro and Michael J. Walte
Observable Consequences of Planet Formation Models in Systems with Close-in Terrestrial Planets
To date, two planetary systems have been discovered with close-in,
terrestrial-mass planets (< 5-10 Earth masses). Many more such discoveries are
anticipated in the coming years with radial velocity and transit searches. Here
we investigate the different mechanisms that could form "hot Earths" and their
observable predictions. Models include: 1) in situ accretion; 2) formation at
larger orbital distance followed by inward "type 1" migration; 3) formation
from material being "shepherded" inward by a migrating gas giant planet; 4)
formation from material being shepherded by moving secular resonances during
dispersal of the protoplanetary disk; 5) tidal circularization of eccentric
terrestrial planets with close-in perihelion distances; and 6)
photo-evaporative mass loss of a close-in giant planet. Models 1-4 have been
validated in previous work. We show that tidal circularization can form hot
Earths, but only for relatively massive planets (> 5 Earth masses) with very
close-in perihelion distances (< 0.025 AU), and even then the net inward
movement in orbital distance is at most only 0.1-0.15 AU. For planets of less
than about 70 Earth masses, photo-evaporation can remove the planet's envelope
and leave behind the solid core on a Gyr timescale, but only for planets inside
0.025-0.05 AU. Using two quantities that are observable by current and upcoming
missions, we show that these models each produce unique signatures, and can be
observationally distinguished. These observables are the planetary system
architecture (detectable with radial velocities, transits and transit-timing)
and the bulk composition of transiting close-in terrestrial planets (measured
by transits via the planet's radius).Comment: Accepted to MNRAS. 14 pages, 4 figures, 1 tabl
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
Performance of the CMS Cathode Strip Chambers with Cosmic Rays
The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device
in the CMS endcaps. Their performance has been evaluated using data taken
during a cosmic ray run in fall 2008. Measured noise levels are low, with the
number of noisy channels well below 1%. Coordinate resolution was measured for
all types of chambers, and fall in the range 47 microns to 243 microns. The
efficiencies for local charged track triggers, for hit and for segments
reconstruction were measured, and are above 99%. The timing resolution per
layer is approximately 5 ns
Performance and Operation of the CMS Electromagnetic Calorimeter
The operation and general performance of the CMS electromagnetic calorimeter
using cosmic-ray muons are described. These muons were recorded after the
closure of the CMS detector in late 2008. The calorimeter is made of lead
tungstate crystals and the overall status of the 75848 channels corresponding
to the barrel and endcap detectors is reported. The stability of crucial
operational parameters, such as high voltage, temperature and electronic noise,
is summarised and the performance of the light monitoring system is presented
EMIP: The eye movements in programming dataset
A large dataset that contains the eye movements of N=216 programmers of different experience levels captured during two code comprehension tasks is presented. Data are grouped in terms of programming expertise (from none to high) and other demographic descriptors. Data were collected through an international collaborative effort that involved eleven research teams across eight countries on four continents. The same eye tracking apparatus and software was used for the data collection. The Eye Movements in Programming (EMIP) dataset is freely available for download. The varied metadata in the EMIP dataset provides fertile ground for the analysis of gaze behavior and may be used to make novel insights about code comprehension
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