C/2018 Y1 (Iwamoto)
Non-periodic comet
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C/2018 Y1 (Iwamoto) is a non-periodic comet with a retrograde orbit discovered on 18 December 2018, by Japanese amateur astronomer Masayuki Iwamoto.[5] Its orbital period is estimated to be 1,733 years, and it passed closest to Earth on 13 February 2019.[6]
Comet Iwamoto photographed by Brandon Ghany on 26 February 2019 | |
| Discovery[1][2] | |
|---|---|
| Discovered by | Masayuki Iwamoto |
| Discovery site | Awa, Tokushima, Japan |
| Discovery date | 18 December 2018 |
| Designations | |
| CK18Y010 | |
| Orbital characteristics[3] | |
| Epoch | 3 March 2019 (JD 2458545.5) |
| Observation arc | 348 days |
| Number of observations | 2,771 |
| Aphelion | 287.25 AU |
| Perihelion | 1.287 AU |
| Semi-major axis | 144.27 AU |
| Eccentricity | 0.9911 |
| Orbital period | 1,733 years |
| Inclination | 160.40° |
| 147.48° | |
| Argument of periapsis | 358.06° |
| Last perihelion | 7 February 2019 |
| TJupiter | –1.286 |
| Earth MOID | 0.299 AU |
| Jupiter MOID | 1.507 AU |
| Physical characteristics | |
| Comet total magnitude (M1) | 13.6 |
| 5.5[4] (2019 apparition) | |
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.[a] 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.[1]
It was expected to reach a magnitude of between 6.5 and 7.5, visible in binoculars or a small telescope.[6][7] On 13 February 2019, Juan Jose Gonzalez reported that it had reached a peak magnitude of 5.5,[4] before fading to 7.6 two weeks later.[8]
Physical characteristics
The comet was observed by iSHELL spectrograph at the NASA Infrared Telescope Facility (IRTF). Overall, the measured spatial distributions for polar molecules (in particular, H
2O and CH
3OH) were broader, exhibiting more complex structure compared with nonpolar or weakly polar species (CH4, C2H6, and CO). Compositionally, compared to their respective mean abundances among comets from the Oort cloud, 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, whereas CH4/C2H6 was unchanged within the uncertainty, suggesting nonhomogeneous composition among regions of the nucleus dominating activity on these dates.[9]
Orbit
Mercury Venus · Earth · Mars · C/2018 Y1
Sun · Uranus · C/2018 Y1
