We use NEOWISE data from the four-band and three-band cryogenic phases of the Wide-field Infrared Survey Explorer mission to constrain size distributions of the comet populations and debias measurements of the short- and long-period comet (LPC) populations. We find that the fit to the debiased LPC population yields a cumulative size−frequency distribution (SFD) power-law slope (β) of −1.0 ± 0.1, while the debiased Jupiter-family comet (JFC) SFD has a steeper slope with β = −2.3 ± 0.2. The JFCs in our debiased sample yielded a mean nucleus size of 1.3 km in diameter, while the LPCs’ mean size is roughly twice as large, 2.1 km, yielding mean size ratios ( ) that differ by a factor of 1.6. Over the course of the 8 months of the survey, our results indicate that the number of LPCs passing within 1.5 au are a factor of several higher than previous estimates, while JFCs are within the previous range of estimates of a few thousand down to sizes near 1.3 km in diameter. Finally, we also observe evidence for structure in the orbital distribution of LPCs, with an overdensity of comets clustered near 110° inclination and perihelion near 2.9 au that is not attributable to observational bias.

The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus sizes, and CO+CO2 production. We present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 μm band excess. We find a possible relation between dust and CO+CO2 production, as well as possible differences in the sizes of long and short period comet nuclei.

The Wide-field Infrared Survey Explorer (WISE) observed 52 Centaurs and Scattered Disk Objects in the thermal infrared, including the 15 discoveries that were new. We present analyses of these observations to estimate sizes and mean optical albedos. We find mean albedos of 0.08 +/- 0.04 for the entire data set. Thermal fits yield average beaming parameters of 0.9 +/- 0.2 that are similar for both SDO and Centaur sub-classes. Biased cumulative size distributions yield size-frequency distribution power law indices ~ -1.7 +/- 0.3. The data also reveal a relation between albedo and color at the 3-sigma level. No significant relation between diameter and albedos is found.

We report results based on mid-infrared photometry of five active main belt objects (AMBOs) detected by the Wide-field Infrared Survey Explorer (WISE) spacecraft. Four of these bodies, P/2010 R2 (La Sagra), 133P/Elst-Pizarro, (596) Scheila, and 176P/LINEAR, showed no signs of activity at the time of the observations, allowing the WISE detections to place firm constraints on their diameters and albedos. Geometric albedos were in the range of a few percent, and on the order of other measured comet nuclei. P/2010 A2 was observed on 2010 April 2–3, three months after its peak activity. Photometry of the coma at 12 and 22 μm combined with ground-based visible-wavelength measurements provides constraints on the dust particle mass distribution (PMD), dlog n/dlog m, yielding power-law slope values of α = −0.5 ± 0.1. This PMD is considerably more shallow than that found for other comets, in particular inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. It is similar to the PMD seen for 9P/Tempel 1 in the immediate aftermath of the Deep Impact experiment. Upper limits for CO2 and CO production are also provided for each AMBO and compared with revised production numbers for WISE observations of 103P/Hartley 2.

On 2010 January 18–19 and June 28–29, the Wide-field Infrared Survey Explorer (WISE) spacecraft imaged the Rosetta mission target, comet 67P/Churyumov-Gerasimenko. We present a preliminary analysis of the images, which provide a characterization of the dust environment at heliocentric distances similar to those planned for the initial spacecraft encounter, but on the outbound leg of its orbit rather than the inbound. Broadband photometry yields low levels of CO2 production at a comet heliocentric distance of 3.32 AU and no detectable production at 4.18 AU. We find that at these heliocentric distances, large dust grains with mean grain diameters on the order of a millimeter or greater dominate the coma and evolve to populate the tail. This is further supported by broadband photometry centered on the nucleus, which yield an estimated differential dust particle size distribution with a power-law relation that is considerably shallower than average. We set a 3σ upper limit constraint on the albedo of the large-grain dust at ⩽0.12. Our best estimate of the nucleus radius (1.82 ± 0.20 km) and albedo (0.04 ± 0.01) are in agreement with measurements previously reported in the literature.

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 mu m 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 mu m 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 mu m 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) x 1024 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 x 10(-10) at a delta mean anomaly of 0.2 deg trailing the comet nucleus, in both 12 and 22 mu m bands. A minimum chi-squared analysis of the dust trail position yields a beta-parameter value of 1.0 x 10(-4), consistent with a derived mean trail-grain diameter of 1.1/rho cm for grains of rho g cm(-3) density. This leads to a total detected trail mass of at least 4 x 10(10) rho kg.