We present preliminary diameters and albedos for 13511 Main Belt asteroids (MBAs) that were observed during the 3-Band Cryo phase of the Wide-field Infrared Survey Explorer (WISE; after the outer ...cryogen tank was exhausted) and as part of the NEOWISE Post-Cryo Survey (after the inner cryogen tank was exhausted). With a reduced or complete loss of sensitivity in the two long wavelength channels of WISE, the uncertainty in our fitted diameters and albedos is increased to ~20% for diameter and ~40% for albedo. Diameter fits using only the 3.4 and 4.6 mu m channels are shown to be dependent on the literature optical H absolute magnitudes. These data allow us to increase the number of size estimates for large MBAs which have been identified as members of dynamical families. We present thermal fits for 14 asteroids previously identified as the parents of a dynamical family that were not observed during the fully cryogenic mission.
The Wide-field Infrared Survey Explorer (WISE) observed 52 Centaurs and scattered disk objects (SDOs) in the thermal infrared, including 15 new discoveries. We present analyses of these observations ...to estimate sizes and mean optical albedos. We find mean albedos of 0.08 + or - 0.04 for the entire data set. Thermal fits yield average beaming parameters of 0.9 + or - 0.2 that are similar for both SDO and Centaur sub-classes. Biased cumulative size distributions yield size-frequency distribution power law indices of ~-1.7 + or - 0.3. The data also reveal a relation between albedo and color at the 3sigma level. No significant relation between diameter and albedos is found.
ABSTRACT The Euphrosyne asteroid family is uniquely situated at high inclination in the outer Main Belt, bisected by the 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 AU, high inclinations, very large eccentricities, and Tisserand parameters similar to Jupiter family comets. Filtering all known Near-Earth objects (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.
Abstract
We present the first results of our survey of asteroid polarization phase curves in the near-infrared
J
and
H
bands using the WIRC+Pol instrument on the Palomar 200-inch telescope. We ...confirm through observations of standard stars that WIRC+Pol can reach the 0.1% precision needed for asteroid phase curve characterization, and we show that C-complex asteroids could act as an alternate calibration source, as they show less wavelength variation than stellar polarized standards. Initial polarization phase curve results for S-complex asteroids show a shift in behavior as a function of wavelength from visible to near-infrared bands, extending previously observed trends. Full near-infrared polarization phase curve characterization of individual asteroids will provide a unique constraint on surface composition of these objects by probing the wavelength dependence of albedo and index of refraction of the surface material.
Automated asteroid detection routines set requirements on the number of detections, signal-to-noise ratio, and the linearity of the expected motion in order to balance completeness, reliability, and ...time delay after data acquisition when identifying moving object tracklets. However, when the full-frame data from a survey are archived, they can be searched later for asteroids that were below the initial detection thresholds. We have conducted such a search of the first three years of the reactivated Near-Earth Object Wide-field Infrared Survey Explorer data, looking for near-Earth objects discovered by ground-based surveys that have previously unreported thermal infrared data. Using these measurements, we can then perform thermal modeling to measure the diameters and albedos of these objects. We present new physical properties for 116 Near-Earth Objects found in this search.
Abstract
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
H
V
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
H
V
magnitude will be fundamentally limited by incomplete phase-curve coverage, incomplete light-curve knowledge, and the necessary conversion from the observed band to the
V
band. Switching the absolute magnitude standard to a different band such a
r
′
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 properly accounted for.
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 that 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.
We report on the observed fluxes of the comets detected by NEOWISE during the first year of operations after the spacecraft’s reactivation. The sample included 57 comets. Of the comets detected, 30 ...were short-period comets (27 Jupiter-family comets, 1 Centaur, 2 Halley-type comets), and 27 were long-period comets. From the measured fluxes in the two NEOWISE bands, proxies for the gas production and coma dust are derived. We find a relationship between heliocentric distance, perihelion distance, and the gas-to-dust proxy fractions.
The NEOWISE data set offers the opportunity to study the variations in albedo for asteroid classification schemes based on visible and near-infrared observations for a large sample of minor planets. ...We have determined the albedos for nearly 1900 asteroids classified by the Tholen, Bus, and Bus-DeMeo taxonomic classification schemes. We find that the S-complex spans a broad range of bright albedos, partially overlapping the low albedo C-complex at small sizes. As expected, the X-complex covers a wide range of albedos. The multiwavelength infrared coverage provided by NEOWISE allows determination of the reflectivity at 3.4 and 4.6 Delta *mm relative to the visible albedo. The direct computation of the reflectivity at 3.4 and 4.6 Delta *mm enables a new means of comparing the various taxonomic classes. Although C, B, D, and T asteroids all have similarly low visible albedos, the D and T types can be distinguished from the C and B types by examining their relative reflectance at 3.4 and 4.6 Delta *mm. All of the albedo distributions are strongly affected by selection biases against small, low albedo objects, as all objects selected for taxonomic classification were chosen according to their visible light brightness. Due to these strong selection biases, we are unable to determine whether or not there are correlations between size, albedo, and space weathering. We argue that the current set of classified asteroids makes any such correlations difficult to verify. A sample of taxonomically classified asteroids drawn without significant albedo bias is needed in order to perform such an analysis.
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