Repeating Gas Ejection Events from Comet 45P/Honda–Mrkos–Pajdušáková

Abstract

Studying materials released from Jupiter-family comets (JFCs)—as seen in their inner comae, 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, multiwavelength observing campaign, we observed comet 45P/Honda–Mrkos–Pajdušáková during its close approach to Earth in 2017 February. 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 in situ observations of other comet nuclei. A repeating feature visible in CN and C2 images on February 16 was also observed on February 17 with an interval of 7.6 ± 0.1 hr, 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 outflow 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 ∼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.

Ulysses spacecraft in situ detections of cometary dust trails

“…Another source of information about particle sizes of cometary dust is radar observations of cometary comae. Observations with the Arecibo observatory planetary radar system showed that the coma of comet 45P/H-M-P contains particles larger than 2 cm [53], while the existence of smaller particles could not be excluded. Single dust impacts in the size range of approximately r d ≈ 1 − 10 µm which likely originated from this comet were also identified in the dust dataset measured with the Helios spacecraft [16].…”

Photometry technique to map elements’ distribution on comets’ nuclei surfaces by using the new method.

“…Each element has many strong emission lines in the visible range (specific colors in the color line). Any comet or rock that has a mixture of elements can be seen in its nucleus when it is directed at several wavelengths from a target [6][7][8], where each wavelength represents a different element received from each pixel of the image. This objective then shows the distributions of many elements on its surface.…”