C/2018 Y1 (Iwamoto)

For the 2013 and 2020 comets of the same name, see C/2013 E2 (Iwamoto) and C/2020 A2 (Iwamoto).

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]

C/2018 Y1 (Iwamoto)

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
Alternative 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°
Longitude of ascending node	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
Apparent magnitude	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

Animation of C/2018 Y1 orbit around the Sun
   Mercury   Venus ·   Earth ·   Mars ·    C/2018 Y1

Animation of C/2018 Y1 orbit 1600-2500
   Sun ·    Uranus ·    C/2018 Y1

Gallery

• 
  Comet C/2018 Y1 (Iwamoto) with M44, 13. February 2019, 23:04 Uhr
• 
  Comet C/2018 Y1 (Iwamoto) with the spiral galaxy NGC 2903, 13 February 2019, 23:19 Uhr
• 
  Comet C/2018 Y1 (Iwamoto) with nebulae IC 410 and IC 405
• 
  C/2018 Y1 (Iwamoto) as seen from the infrared telescope NEOWISE on 25 February 2019

See also

• C/2018 V1 (Machholz–Fujikawa–Iwamoto)