C/2018 Y1 (Iwamoto)

C/2018 Y1 is a non-periodic comet with a retrograde orbit discovered on 18 December 2018, by Japanese amateur astronomer Masayuki Iwamoto. Its orbital period is estimated to be 1,733 years, and it passed closest to Earth on 13 February 2019.

Observational history

Nearly a month after co-discovering C/2018 V1 (Machholz–Fujikawa–Iwamoto), Masayuki Iwamoto spotted another comet on 18 December 2018, which was moving north on the constellation Hydra. Shuichi Nakano noted that the 13th-magnitude object has a blue coma, where he also provided initial orbital calculations using Iwamoto's images two days later.
It was expected to reach a magnitude of between 6.5 and 7.5, visible in binoculars or a small telescope. On 13 February 2019, Juan Jose Gonzalez reported that it had reached a peak magnitude of 5.5, before fading to 7.6 two weeks later.

Physical characteristics

The comet was observed by iSHELL spectrograph at the NASA Infrared Telescope Facility. Overall, the measured spatial distributions for polar molecules were broader, exhibiting more complex structure compared with nonpolar or weakly polar species. Compositionally, compared to their respective mean abundances among comets from the Oort cloud, and were enriched, and HCN were near normal, and all other species were depleted. The abundance ratio / was higher by % on January 13 versus February 5, whereas was unchanged within the uncertainty, suggesting nonhomogeneous composition among regions of the nucleus dominating activity on these dates.