A Survey of Cometary Dust Tails in the NEOWISE Data

NEOWISE is the planetary-funded mission that utilizes data from the Wide-field Infrared Survey Explorer (WISE) spacecraft to detect and characterize moving objects [1, 2]. During the course of the prime mission (January 2010 and February 2011), over 160 comets were serendipitously observed, including 22 newly discovered comets, from both the long period (LPC) and short period (SPC) comet populations. Over half of the comets observed by NEOWISE displayed a significant dust tail in the 12 and 22-micron (thermal emission) bands, showing a wide range of activity levels and dust morphology.

Each comet was serendipitously observed multiple times by NEOWISE, and the individual images were stacked to increase the signal-to-noise ratio. For the comets that displayed a significant dust tail, we have estimated the sizes and ages of the particles using dynamical models based on the Finson-Probstein method [3, 4]. These models were then compared to the data using either a “by eye” method, or an analytical technique, depending on the data quality [5, 6]. For comets that were observed multiple times by WISE, the dust tail particle properties were estimated separately, and then compared.

We find that the dust tails of both LPCs and SPCs are primarily comprised of ~mm to cm sized particles, which were the result of emission that occurred several months to several years prior to the observations. Both LPCs and SPCs have strong large grain dust emission close to the comet’s perihelion distance, with some SPCs showing strong emission well before perihelion. When comparing the two populations as a whole, we find that there is no statistical difference in the size of the particles between the two populations. Similar sized particles suggest similar internal structure and possibly a similar origin for the two populations. Further implications of these results will also be discussed.

Government funding acknowledged.

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