The Perihelion Emission of Comet C/2010 L5 ( WISE )

The only Halley-type comet discovered by the Wide-Field Infrared Survey Explorer ( WISE ), C/2010 L5 ( WISE ), was imaged three times by WISE , and it showed a significant dust tail during the second and third visits (2010 June and July, respectively). We present here an analysis of the data collected by WISE , putting estimates on the comet's size, dust production rate, gas production (CO+CO₂) rate, and active fraction. We also present a detailed description of a novel tail-fitting technique that allows the commonly used syndyne–synchrone models to be used analytically, thereby giving more robust results. We find that C/2010 L5's dust tail was likely formed by strong emission, likely in the form of an outburst, occurring when the comet was within a few days of perihelion. Analyses of the June and July data independently agree on this result. The two separate epochs of dust tail analysis independently suggest a strong emission event close to perihelion. The average size of the dust particles in the dust tail increased between the epochs, suggesting that the dust was primarily released in a short period of time, and the smaller dust particles were quickly swept away by solar radiation pressure, leaving the larger particles behind. The difference in CO₂ and dust production rates measured in 2010 June and July is not consistent with "normal" steady-state gas production from a comet at these heliocentric distances, suggesting that much of the detected CO₂ and dust was produced in an episodic event. Together, these conclusions suggest that C/2010 L5 experienced a significant outburst event when the comet was close to perihelion.