Lingering grains of truth around comet 17P/Holmes

Comet 17P/Holmes underwent a massive outburst in 2007 Oct., brightening by a factor of almost a million in under 48 hours. We used infrared images taken by the Wide-Field Survey Explorer mission to characterize the comet as it appeared at a heliocentric distance of 5.1 AU almost 3 years after the outburst. The comet appeared to be active with a coma and dust trail along the orbital plane. We constrained the diameter, albedo, and beaming parameter of the nucleus to 4.135 $\pm$ 0.610 km, 0.03 $\pm$ 0.01 and 1.03 $\pm$ 0.21, respectively. The properties of the nucleus are consistent with those of other Jupiter Family comets. The best-fit temperature of the coma was 134 $\pm$ 11 K, slightly higher than the blackbody temperature at that heliocentric distance. Using Finson-Probstein modeling we found that the morphology of the trail was consistent with ejection during the 2007 outburst and was made up of dust grains between 250 $\mu$m and a few cm in radius. The trail mass was $\sim$ 1.2 - 5.3 $\times$ 10$^{10}$ kg.Comment: Accepted to ApJ. 2 tables, 4 figure

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

Survey Simulations of a New Near-Earth Asteroid Detection System

We have carried out simulations to predict the performance of a new space-based telescopic survey operating at thermal infrared wavelengths that seeks to discover and characterize a large fraction of the potentially hazardous near-Earth asteroid (NEA) population. Two potential architectures for the survey were considered: one located at the Earth-Sun L1 Lagrange point, and one in a Venus-trailing orbit. A sample cadence was formulated and tested, allowing for the self-follow-up necessary for objects discovered in the daytime sky on Earth. Synthetic populations of NEAs with sizes >=140 m in effective spherical diameter were simulated using recent determinations of their physical and orbital properties. Estimates of the instrumental sensitivity, integration times, and slew speeds were included for both architectures assuming the properties of new large-format 10 um detector arrays capable of operating at ~35 K. Our simulation included the creation of a preliminary version of a moving object processing pipeline suitable for operating on the trial cadence. We tested this pipeline on a simulated sky populated with astrophysical sources such as stars and galaxies extrapolated from Spitzer and WISE data, the catalog of known minor planets (including Main Belt asteroids, comets, Jovian Trojans, etc.), and the synthetic NEA model. Trial orbits were computed for simulated position-time pairs extracted from the synthetic surveys to verify that the tested cadence would result in orbits suitable for recovering objects at a later time. Our results indicate that the Earth-Sun L1 and Venus-trailing surveys achieve similar levels of integral completeness for potentially hazardous asteroids larger than 140 m; placing the telescope in an interior orbit does not yield an improvement in discovery rates. This work serves as a necessary first step for the detailed planning of a next-generation NEA survey.Comment: AJ accepted; corrected typ

Thermal Model Calibration for Minor Planets Observed with Wide-Field Infrared Survey Explorer/Neowise

With the Wide-field Infrared Survey Explorer (WISE), we have observed over 157,000 minor planets. Included in these are a number of near-Earth objects, main-belt asteroids, and irregular satellites which have well measured physical properties (via radar studies and in situ imaging) such as diameters. We have used these objects to validate models of thermal emission and reflected sunlight using the WISE measurements, as well as the color corrections derived in Wright et al. for the four WISE bandpasses as a function of effective temperature. We have used 50 objects with diameters measured by radar or in situ imaging to characterize the systematic errors implicit in using the WISE data with a faceted spherical near-Earth asteroid thermal model (NEATM) to compute diameters and albedos. By using the previously measured diameters and H magnitudes with a spherical NEATM model, we compute the predicted fluxes (after applying the color corrections given in Wright et al.) in each of the four WISE bands and compare them to the measured magnitudes. We find minimum systematic flux errors of 5%-10%, and hence minimum relative diameter and albedo errors of ~10% and ~20%, respectively. Additionally, visible albedos for the objects are computed and compared to the albedos at 3.4 μm and 4.6 μm, which contain a combination of reflected sunlight and thermal emission for most minor planets observed by WISE. Finally, we derive a linear relationship between subsolar temperature and effective temperature, which allows the color corrections given in Wright et al. to be used for minor planets by computing only subsolar temperature instead of a faceted thermophysical model. The thermal models derived in this paper are not intended to supplant previous measurements made using radar or spacecraft imaging; rather, we have used them to characterize the errors that should be expected when computing diameters and albedos of minor planets observed by WISE using a spherical NEATM model