72 research outputs found
The Mission Accessible Near-Earth Objects Survey: Four years of photometry
Over 4.5 years, the Mission Accessible Near-Earth Object Survey (MANOS)
assembled 228 Near-Earth Object (NEO) lightcurves. We report rotational
lightcurves for 82 NEOs, constraints on amplitudes and periods for 21 NEOs,
lightcurves with no detected variability within the image signal to noise and
length of our observing block for 30 NEOs, and 10 tumblers. We uncovered 2
ultra-rapid rotators with periods below 20s; 2016MA with a potential rotational
periodicity of 18.4s, and 2017QG rotating in 11.9s, and estimate the
fraction of fast/ultra-rapid rotators undetected in our project plus the
percentage of NEOs with a moderate/long periodicity undetectable during our
typical observing blocks. We summarize the findings of a simple model of
synthetic NEOs to infer the object morphologies distribution using the measured
distribution of lightcurve amplitudes. This model suggests a uniform
distribution of axis ratio can reproduce the observed sample. This suggests
that the quantity of spherical NEOs (e.g., Bennu) is almost equivalent to the
quantity of highly elongated objects (e.g., Itokawa), a result that can be
directly tested thanks to shape models from Doppler delay radar imaging
analysis. Finally, we fully characterized 2 NEOs as appropriate targets for a
potential robotic/human mission: 2013YS and 2014FA due to their
moderate spin periods and low .Comment: Accepted for Publication, The Astrophysical Journal Supplement Serie
Red material on the large moons of Uranus: Dust from irregular satellites?
The large and tidally-locked classical moons of Uranus display longitudinal
and planetocentric trends in their surface compositions. Spectrally red
material has been detected primarily on the leading hemispheres of the outer
moons, Titania and Oberon. Furthermore, detected H2O ice bands are stronger on
the leading hemispheres of the classical satellites, and the leading/trailing
asymmetry in H2O ice band strengths decreases with distance from Uranus. We
hypothesize that the observed distribution of red material and trends in H2O
ice band strengths results from infalling dust from Uranian irregular
satellites. These dust particles migrate inward on slowly decaying orbits,
eventually reaching the classical satellite zone, where they collide primarily
with the outer moons. The latitudinal distribution of dust swept up by these
moons should be fairly even across their southern and northern hemispheres.
However, red material has only been detected over the southern hemispheres of
these moons (subsolar latitude 81 S). Consequently, to test whether irregular
satellite dust impacts drive the observed enhancement in reddening, we have
gathered new ground-based data of the now observable northern hemispheres of
these moons (sub-observer latitudes, 17 to 35 N). Our results and analyses
indicate that longitudinal and planetocentric trends in reddening and H2O ice
band strengths are broadly consistent across both southern and northern
latitudes of these moons, thereby supporting our hypothesis. Utilizing a suite
of numerical best fit models, we investigate the composition of the reddening
agent detected on these moons, finding that both complex organics and amorphous
pyroxene match the spectral slopes of our data. We also present spectra that
span 2.9 to 4.1 microns, a previously unexplored wavelength range in terms of
spectroscopy for the Uranian moons.Comment: Icarus [In Press]. 12 figures, 15 table
A 2km-size asteroid challenging the rubble-pile spin barrier â A case for cohesion
The rubble pile spin barrier is an upper limit on the rotation rate of asteroids larger than ~200-300. m. Among thousands of asteroids with diameters larger than ~300. m, only a handful of asteroids are known to rotate faster than 2.0. h, all are in the sub-km range (â€0.6. km). Here we present photometric measurements suggesting that (60716) 2000 GD65, an S-complex, inner-main belt asteroid with a relatively large diameter of 2.3-0.7+0.6km, completes one rotation in 1.9529. ±. 0.0002. h. Its unique diameter and rotation period allow us to examine scenarios about asteroid internal structure and evolution: a rubble pile bound only by gravity; a rubble-pile with strong cohesion; a monolithic structure; an asteroid experiencing mass shedding; an asteroid experiencing YORP spin-up/down; and an asteroid with a unique octahedron shape results with a four-peak lightcurve and a 3.9. h period. We find that the most likely scenario includes a lunar-like cohesion that can prevent (60716) 2000 GD65 from disrupting without requiring a monolithic structure or a unique shape. Due to the uniqueness of (60716) 2000 GD65, we suggest that most asteroids typically have smaller cohesion than that of lunar regolith. Keywords: Asteroids; Asteroids, rotation; Rotational dynamics; PhotometryUnited States. National Aeronautics and Space Administration (Grant NNX12AL26G
Giant planet migration, disk evolution, and the origin of transitional disks
We present models of giant planet migration in evolving protoplanetary disks.
Our disks evolve subject to viscous transport of angular momentum and
photoevaporation, while planets undergo Type II migration. We use a Monte Carlo
approach, running large numbers of models with a range in initial conditions.
We find that relatively simple models can reproduce both the observed radial
distribution of extra-solar giant planets, and the lifetimes and accretion
histories of protoplanetary disks. The use of state-of-the-art photoevaporation
models results in a degree of coupling between planet formation and disk
clearing, which has not been found previously. Some accretion across planetary
orbits is necessary if planets are to survive at radii <~1.5AU, and if planets
of Jupiter mass or greater are to survive in our models they must be able to
form at late times, when the disk surface density in the formation region is
low. Our model forms two different types of "transitional" disks, embedded
planets and clearing disks, which show markedly different properties. We find
that the observable properties of these systems are broadly consistent with
current observations, and highlight useful observational diagnostics. We
predict that young transition disks are more likely to contain embedded giant
planets, while older transition disks are more likely to be undergoing disk
clearing.Comment: 13 pages, 9 figures. Accepted for publication in Ap
The Roles of Tidal Evolution and Evaporative Mass Loss in the Origin of CoRoT-7 b
CoRoT-7 b is the first confirmed rocky exoplanet, but, with an orbital
semi-major axis of 0.0172 AU, its origins may be unlike any rocky planet in our
solar system. In this study, we consider the roles of tidal evolution and
evaporative mass loss in CoRoT-7 b's history, which together have modified the
planet's mass and orbit. If CoRoT-7 b has always been a rocky body, evaporation
may have driven off almost half its original mass, but the mass loss may depend
sensitively on the extent of tidal decay of its orbit. As tides caused CoRoT-7
b's orbit to decay, they brought the planet closer to its host star, thereby
enhancing the mass loss rate. Such a large mass loss also suggests the
possibility that CoRoT-7 b began as a gas giant planet and had its original
atmosphere completely evaporated. In this case, we find that CoRoT-7 b's
original mass probably didn't exceed 200 Earth masses (about 2/3 of a Jupiter
mass). Tides raised on the host star by the planet may have significantly
reduced the orbital semi-major axis, perhaps causing the planet to migrate
through mean-motion resonances with the other planet in the system, CoRoT-7 c.
The coupling between tidal evolution and mass loss may be important not only
for CoRoT-7 b but also for other close-in exoplanets, and future studies of
mass loss and orbital evolution may provide insight into the origin and fate of
close-in planets, both rocky and gaseous.Comment: Accepted for publication by MNRAS on 2010 May
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
- âŠ