168P/Hergenrother

Observational history

Discovery

On 22 November 1998, Carl W. Hergenrother spotted a new comet from CCD images taken by Timothy B. Spahr a day earlier with the Catalina Sky Survey's 0.41 m telescope. Preliminary orbital calculations by Brian G. Marsden reveal that the comet has a periodic orbit of 6.78 years. At the time, the comet was a 17th-magnitude object within the constellation Ursa Minor.

Between 2000 and 2002, Kazuo Kinoshita and Shuichi Nakano independently used the comet's positions during its 1998 apparition to predict its next perihelion date, which is around 2 November 2005. It was successfully recovered by Australian astronomer, David Herald, on 6 November 2005.

2012 outburst

The comet came to perihelion on 1 October 2012, and was expected to reach about apparent magnitude 15.2, but due to an outburst the comet reached apparent magnitude 8. As a result of the outburst of gas and dust, the comet was briefly more than 500 times brighter than it would have been without the outburst. On 19 October, images by the Virtual Telescope Project showed a dust cloud trailing the nucleus. Images by the 2 m Faulkes Telescope North on 26 October, confirm a fragmentation event. The secondary fragment was about magnitude 17. Further observations by the 8.1 m Gemini telescope show that the comet fragmented into at least four parts in six fragmentation events.

2019 apparition

168P came to perihelion on 5 August 2019, when it was 76 degrees from the Sun. It then made a closest approach to Earth on 6 November 2019, when it was 1 AU from Earth with a solar elongation of about 110 degrees. It was not recovered until 3 January 2020, when it was 141 degrees from the Sun, but only two observations on a single night were reported.

Physical characteristics

Observations conducted by the Spitzer Space Telescope between 2006 and 2007 showed that Hergenrother's nucleus was originally about 0.96 km in diameter before it fragmented on its 2012 outburst. This was later revised to 0.91 km upon reanalysis of data in 2020.

References

Notes

Citations

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