C/2018 Y1 (Iwamoto)
Non-periodic comet discovered by Masayuki Iwamoto in December 2018.
C/2018 Y1 (Iwamoto) is a non-periodic comet that follows a retrograde orbit. Japanese amateur astronomer Masayuki Iwamoto discovered it on 18 December 2018. Its orbital period is estimated at 1,733 years, and it made its closest approach to Earth on 13 February 2019.
Iwamoto spotted the comet moving northward in the constellation Hydra, less than a month after co-discovering another comet, C/2018 V1. Two days later, Shuichi Nakano used Iwamoto’s images to provide initial orbital calculations, noting the 13th-magnitude object had a blue coma. Astronomers expected it to reach a magnitude between 6.5 and 7.5, visible with binoculars or a small telescope. On 13 February 2019, Juan Jose Gonzalez reported it had peaked at magnitude 5.5, then faded to 7.6 two weeks afterward.
Observations with the iSHELL spectrograph at the NASA Infrared Telescope Facility showed that polar molecules like H₂O and CH₃OH had broader spatial distributions and more complex structures than nonpolar or weakly polar species such as CH₄, C₂H₆, and CO. Compared to average abundances among Oort cloud comets, C₂H₆ and CH₃OH were enriched, CH₄ and HCN were near normal, and all other species were depleted. The CH₃OH/C₂H₆ ratio was 45±8% higher on 13 January than on 5 February, while the CH₄/C₂H₆ ratio remained unchanged within uncertainty, suggesting the comet’s nucleus had nonhomogeneous composition across the regions driving activity on those dates.
Quick Facts
- Discovery Ref
- CBET_4588 · MPEC_2018-Y52
- Discoverer
- Masayuki Iwamoto
- Discovery Site
- Awa, Tokushima, Japan
- Discovery Date
- 18 December 2018
- Designations
- CK18Y010
- Orbit Ref
- jpl
- Epoch
- 3 March 2019 (JD 2458545.5)
- Observation Arc
- 348 days
- Obs
- 2,771
- Perihelion
- 1.287 AU
- Aphelion
- 287.25 AU
- Semimajor
- 144.27 AU
Facts from the source article.
Lore & Background
Nearly a month after co-discovering C/2018 V1 (Machholz–Fujikawa–Iwamoto), Masayuki Iwamoto spotted another comet on 18 December 2018, moving north in the constellation Hydra. Shuichi Nakano noted that the 13th-magnitude object had a blue coma and provided initial orbital calculations using Iwamoto's images from two days later. The comet was expected to reach a magnitude between 6.5 and 7.5, but on 13 February 2019, Juan Jose Gonzalez reported it had reached a peak magnitude of 5.5, before fading to 7.6 two weeks later.
The comet was observed by the iSHELL spectrograph at the NASA Infrared Telescope Facility (IRTF). The measured spatial distributions for polar molecules (H2O and CH3OH) were broader and more complex compared with nonpolar or weakly polar species (CH4, C2H6, and CO). Compositionally, relative to mean abundances among Oort cloud comets, C2H6 and CH3OH were enriched, CH4 and HCN were near normal, and all other species were depleted. The abundance ratio CH3OH/C2H6 was higher by 45±8% on January 13 versus February 5, while CH4/C2H6 was unchanged within uncertainty, suggesting nonhomogeneous composition among regions of the nucleus dominating activity on those dates.
Reader's Guide
C/2018 Y1 (Iwamoto) is notable as the second comet discovered by Masayuki Iwamoto within a short span, following C/2018 V1 (Machholz–Fujikawa–Iwamoto). Its retrograde, non-periodic orbit with an estimated period of 1,733 years places it among long-period comets from the Oort cloud. The comet's brightness peaked at magnitude 5.5, slightly brighter than initial predictions, allowing observation with binoculars or small telescopes. Spectroscopic observations at the IRTF revealed compositional heterogeneity in the nucleus, with enrichment of C2H6 and CH3OH relative to typical Oort cloud comets, and a significant change in the CH3OH/C2H6 ratio between January and February 2019. This suggests that different regions of the nucleus dominated activity at different times, providing insight into the internal structure and composition of long-period comets. The comet's blue coma and complex molecular distributions contribute to understanding the diversity of cometary chemistry.
Did You Know?
- The comet was discovered by Japanese amateur astronomer Masayuki Iwamoto on 18 December 2018.
- It has a retrograde orbit with an estimated orbital period of 1,733 years.
- It reached a peak magnitude of 5.5 on 13 February 2019, visible in binoculars or a small telescope.
- Spectroscopic observations showed enrichment of C2H6 and CH3OH compared to typical Oort cloud comets.
More in Named Comets, Part 4 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced