Repeating gas ejection events from comet 45P/Honda-Mrkos-Pajdu\v{s}\'{a}kov\'{a}

TL;DR

This study observed repeating gas ejection events from comet 45P/Honda-Mrkos-Pajduškáová, revealing heterogeneity in source regions, a consistent rotation period, and quantifying material release per cycle, enhancing understanding of comet activity.

Contribution

It provides the first detailed observation of a repeating CN jet in a Jupiter-family comet, linking it to the comet's rotation and local activity patterns.

Findings

Revealed heterogeneity in volatile source regions.

Detected a repeating CN jet with a 7.6-hour period.

Quantified material released per cycle (~9.2 kg).

Abstract

Studying materials released from Jupiter-family comets (JFCs) -- as seen in their inner com\ae, the envelope of gas and dust that forms as the comet approaches the Sun -- improves the understanding of their origin and evolutionary history. As part of a coordinated, multi-wavelength observing campaign, we observed comet 45P/Honda-Mrkos-Pajdu\v{s}\'{a}kov\'{a} during its close approach to Earth in February 2017. Narrowband observations were taken using the Bok 90" telescope at Kitt Peak National Observatory 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 and \textit{in situ} observations of other comet nuclei. A repeating feature visible in CN and C$_2$ images on February 16 was also observed on February 17 with an interval of $7.6\pm0.1$ hours, consistent with the rotation period of the comet derived from Arecibo Observatory radar observations. The repeating feature's projected gas velocity away from the nucleus is 0.8 km s$^{-1}$, with an expansion velocity of 0.5 km s$^{-1}$. A bright compact spot adjacent to the nucleus provides a lower limit of the amount of material released in one cycle of $\sim$9.2 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; however, similar features could be obscured by other processes and daughter product species when viewed from distances further than the scale length of CN molecules.