Studying materials released from Jupiter-family comets (JFCs) as seen in their inner comae, the envelope of gas and dust forming as the comet approaches the Sun, provides an improved understanding of their origin and evolutionary history. As part of a coordinated, multi-wavelength observing campaign, we observed comet 45P/Honda-Mrkos-Pajduv{s}{a}kov{a} during its close approach to Earth in February 2017. Narrowband observations were taken using the Bok 90 telescope at KPNO on February 16 and 17 UT, revealing gas and dust structures. We observed different jet directions for different volatile species, implying source region heterogeneity, consistent with other ground-based as well as in situ observations of comet nuclei. A repeating feature visible in CN and C$_2$ images on February 16, was recovered on February 17 with an interval of $7.6pm0.1$ hours, consistent with the rotation period of the comet derived from Arecibo Observatory radar observations. The repeating features projected gas velocity away from the nucleus is 0.8 km/s, with an expansion velocity as 0.5 km/s. The amount of CN material released in one cycle has a lower limit of 11 kg, depending on composition, a quantity small enough to be produced by repeated exposure of nucleus ices to sunlight. This repeating CN jet forming within 400 km of the nucleus may be typical of inner coma behavior in JFCs. Similar repeating CN features could exist and be common in other observed comets, but obscured by other processes and daughter product species as viewed from distances further than the scale length of CN molecules.
تحميل البحث