WISE/NEOWISE OBSERVATIONS OF COMET 103P/HARTLEY 2

Abstract

We report results based on mid-infrared photometry of comet 103P/Hartley 2 taken during 2010 May 4-13 (when the comet was at a heliocentric distance of 2.3 AU, and an observer distance of 2.0 AU) by the Wide-field Infrared Survey Explorer. Photometry of the coma at 22 μm and data from the University of Hawaii 2.2 m telescope obtained on 2010 May 22 provide constraints on the dust particle size distribution, d log n/d log m, yielding power-law slope values of alpha = −0.97 ± 0.10, steeper than that found for the inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. The extracted nucleus signal at 12 μm is consistent with a body of average spherical radius of 0.6 ± 0.2 km (one standard deviation), assuming a beaming parameter of 1.2. The 4.6 μm band signal in excess of dust and nucleus reflected and thermal contributions may be attributed to carbon monoxide or carbon dioxide emission lines and provides limits and estimates of species production. Derived carbon dioxide coma production rates are 3.5(± 0.9) × 10 24 molecules per second. Analyses of the trail signal present in the stacked image with an effective exposure time of 158.4 s yields optical-depth values near 9 × 10 −10 at a delta mean anomaly of 0.2 deg trailing the comet nucleus, in both 12 and 22 μm bands. A minimum chi-squared analysis of the dust trail position yields a beta-parameter value of 1.0 × 10 −4 , consistent with a derived mean trail-grain diameter of 1.1/ρ cm for grains of ρ g cm −3 density. This leads to a total detected trail mass of at least 4 × 10 10 ρ kg.

Space-Based Thermal Infrared Studies of Asteroids

“…Mid-IR spectra have also proven useful for constraining the abundance of volatiles on small bodies; for example, many species such as CO and CO 2 have been identified on comets photometrically through excess flux above their thermal emission (e.g. Bauer et al 2011;Reach et al 2013). Recently, Herschel heterodyne spectroscopy of the largest object in the Main Belt, (1) Ceres, has revealed the presence of water vapor as the dwarf planet approached perihelion (Küppers et al 2014).…”

WISE/NEOWISE PRELIMINARY ANALYSIS AND HIGHLIGHTS OF THE 67P/CHURYUMOV-GERASIMENKO NEAR NUCLEUS ENVIRONS

“…Scaling the dust blackbody curve and expected reflectance given a standard α = −3 power law for the particle size distribution (PSD; cf. Fulle 2004), with a neutral reflectance and a reflectance reddening law based on Jewitt & Meech (1986) averaged out to 3.5 μm, we employ the method from Bauer et al (2011) to determine the excess flux. This is somewhat conservative in its approach for this particular comet, as the PSD is quite flattened relative to the standard PSD for 67P at these distances (see below).…”

“…We emphasize that the detection is only 2σ above the dust flux estimates for W2. Using the methods outlined by Pittichová et al (2008) and applied in the case of the WISE filter bands in Bauer et al (2011Bauer et al ( , 2012, we find the production rate estimates listed in Table 2. We find no excess in the VB signal, and indeed no significant W2 signal at that time.…”

Lingering Grains of Truth Around Comet 17p/Holmes

“…Reach et al (2010) and Boissier et al (2012) detected a slower moving core-component of the largest grains that separated from the nucleus at a relative velocity of ∼7-9 m s −1 . Large dust grains may persist in the vicinity or along the trail of a comet for years after ejection from the nucleus (Sykes et al 1990;Lisse et al 1998;Bauer et al 2011). In this work we used infrared (IR) images obtained with the Wide-Field Infrared Survey Explorer (WISE) to examine the evolution of 17P several years after the 2007 outburst.…”