134 research outputs found
Revising the age for the Baptistina asteroid family using WISE/NEOWISE data
We have used numerical routines to model the evolution of a simulated
Baptistina family to constrain its age in light of new measurements of the
diameters and albedos of family members from the Wide-field Infrared Survey
Explorer. We also investigate the effect of varying the assumed physical and
orbital parameters on the best-fitting age. We find that the physically allowed
range of assumed values for the density and thermal conductivity induces a
large uncertainty in the rate of evolution. When realistic uncertainties in the
family members' physical parameters are taken into account we find the
best-fitting age can fall anywhere in the range of 140-320 Myr. Without more
information on the physical properties of the family members it is difficult to
place a more firm constraint on Baptistina's age.Comment: 27 pages, 16 figures, accepted to Ap
A revised asteroid polarization-albedo relationship using WISE/NEOWISE data
We present a reanalysis of the relationship between asteroid albedo and
polarization properties using the albedos derived from the Wide-field Infrared
Survey Explorer. We find that the function that best describes this relation is
a three-dimensional linear fit in the space of log(albedo)-log(polarization
slope)-log(minimum polarization). When projected to two dimensions the
parameters of the fit are consistent with those found in previous work. We also
define p* as the quantity of maximal polarization variation when compared with
albedo and present the best fitting albedo-p* relation. Some asteroid taxonomic
types stand out in this three-dimensional space, notably the E, B, and M Tholen
types, while others cluster in clumps coincident with the S- and C-complex
bodies. We note that both low albedo and small (D<30 km) asteroids are
under-represented in the polarimetric sample, and we encourage future
polarimetric surveys to focus on these bodies.Comment: 16 pages, Accepted to Ap
The Albedo Distribution of Near Earth Asteroids
The cryogenic WISE mission in 2010 was extremely sensitive to asteroids and
not biased against detecting dark objects. The albedos of 428 Near Earth
Asteroids (NEAs) observed by WISE during its fully cryogenic mission can be fit
quite well by a 3 parameter function that is the sum of two Rayleigh
distributions. The Rayleigh distribution is zero for negative values, and
follows for positive x. The peak
value is at x=\sigma, so the position and width are tied together. The three
parameters are the fraction of the objects in the dark population, the position
of the dark peak, and the position of the brighter peak. We find that 25.3% of
the NEAs observed by WISE are in a very dark population peaking at , while the other 74.7% of the NEAs seen by WISE are in a moderately dark
population peaking at . A consequence of this bimodal distribution
is that the Congressional mandate to find 90% of all NEAs larger than 140 m
diameter cannot be satisfied by surveying to H=22 mag, since a 140 m diameter
asteroid at the very dark peak has H=23.7 mag, and more than 10% of NEAs are
darker than p_V = 0.03.Comment: 7 pages LaTex, 4 figures, accepted for publication in the
Astronomical Journa
The Euphrosyne family's contribution to the low albedo near-Earth asteroids
The Euphrosyne asteroid family is uniquely situated at high inclination in
the outer Main Belt, bisected by the nu_6 secular resonance. This large, low
albedo family may thus be an important contributor to specific subpopulations
of the near-Earth objects. We present simulations of the orbital evolution of
Euphrosyne family members from the time of breakup to the present day, focusing
on those members that move into near-Earth orbits. We find that family members
typically evolve into a specific region of orbital element-space, with
semimajor axes near ~3 AU, high inclinations, very large eccentricities, and
Tisserand parameters similar to Jupiter family comets. Filtering all known NEOs
with our derived orbital element limits, we find that the population of
candidate objects is significantly lower in albedo than the overall NEO
population, although many of our candidates are also darker than the Euphrosyne
family, and may have properties more similar to comet nuclei. Followup
characterization of these candidates will enable us to compare them to known
family properties, and confirm which ones originated with the breakup of (31)
Euphrosyne.Comment: Accepted for publication in Ap
Asteroid family identification using the Hierarchical Clustering Method and WISE/NEOWISE physical properties
Using albedos from WISE/NEOWISE to separate distinct albedo groups within the
Main Belt asteroids, we apply the Hierarchical Clustering Method to these
subpopulations and identify dynamically associated clusters of asteroids. While
this survey is limited to the ~35% of known Main Belt asteroids that were
detected by NEOWISE, we present the families linked from these objects as
higher confidence associations than can be obtained from dynamical linking
alone. We find that over one-third of the observed population of the Main Belt
is represented in the high-confidence cores of dynamical families. The albedo
distribution of family members differs significantly from the albedo
distribution of background objects in the same region of the Main Belt, however
interpretation of this effect is complicated by the incomplete identification
of lower-confidence family members. In total we link 38,298 asteroids into 76
distinct families. This work represents a critical step necessary to debias the
albedo and size distributions of asteroids in the Main Belt and understand the
formation and history of small bodies in our Solar system.Comment: Accepted to ApJ. Full version of Table 3 to be published
electronically in Ap
Uncertainties on Asteroid Albedos Determined by Thermal Modeling
We present an analysis of the accuracy of geometric albedos determined for
asteroids through the modeling of observed thermal infrared radiation. We show
that albedo uncertainty is dominated by the uncertainty on the measured
absolute magnitude, and that any analysis using albedos in a statistical
application will also be dominated by this source of uncertainty. For all but
the small fraction of asteroids with a large amount of characterization data,
improved knowledge of the magnitude will be fundamentally limited by
incomplete phase curve coverage, incomplete light curve knowledge, and the
necessary conversion from the observed band to the band. Switching the
absolute magnitude standard to a different band such a would mitigate the
uncertainty due to band conversion for many surveys, but this only represents a
small component of the total uncertainty. Therefore, techniques making use of
these albedos must ensure that their uncertainties are being properly accounted
for.Comment: 10 pages, 1 figure. Accepted to the Planetary Science Journa
Main Belt Asteroids with WISE/NEOWISE: Near-Infrared Albedos
We present revised near-infrared albedo fits of 2835 Main Belt asteroids
observed by WISE/NEOWISE over the course of its fully cryogenic survey in 2010.
These fits are derived from reflected-light near-infrared images taken
simultaneously with thermal emission measurements, allowing for more accurate
measurements of the near-infrared albedos than is possible for visible albedo
measurements. As our sample requires reflected light measurements, it
undersamples small, low albedo asteroids, as well as those with blue spectral
slopes across the wavelengths investigated. We find that the Main Belt
separates into three distinct groups of 6%, 16%, and 40% reflectance at 3.4 um.
Conversely, the 4.6 um albedo distribution spans the full range of possible
values with no clear grouping. Asteroid families show a narrow distribution of
3.4 um albedos within each family that map to one of the three observed
groupings, with the (221) Eos family being the sole family associated with the
16% reflectance 3.4 um albedo group. We show that near-infrared albedos derived
from simultaneous thermal emission and reflected light measurements are an
important indicator of asteroid taxonomy and can identify interesting targets
for spectroscopic followup.Comment: Accepted for publication in ApJ; full version of Table1 to be
published electronically in the journa
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