C/1988 Y1 (Yanaka)

C/1988 Y1 (Yanaka) is a non-periodic comet that was discovered by Japanese astronomer, Tetsuo Yanaka, in December 1988. Spectral observations of the comet showed that it is depleted in carbon and cyanogen compounds that is typically found in other comets,^[6] a trait only shared by 96P/Machholz.^[7]

C/1988 Y1 (Yanaka)

Discovery[1]
Discovered by	Tetsuo Yanaka
Discovery site	Motegi, Japan
Discovery date	29 December 1988
Designations
Alternative designations	1988 XXIV, 1988r[2]
Orbital characteristics[3][4]
Epoch	12 January 1989 (JD 2447538.5)
Observation arc	57 days
Number of observations	56
Perihelion	0.428 AU
Eccentricity	1.000187
Inclination	71.011°
Longitude of ascending node	315.52°
Argument of periapsis	88.122°
Last perihelion	11 December 1988
Earth MOID	0.069 AU
Jupiter MOID	3.584 AU
Physical characteristics[5]
Mean radius	0.194 km (0.121 mi)[a]
Comet total magnitude (M1)	12.4
Comet nuclear magnitude (M2)	17.7
Apparent magnitude	9.0–9.5 (1988 apparition)

Observational history

Discovery

Tetsuo Yanaka discovered this comet using a pair of 25 x 150 binoculars on the night of 29 December 1988. At the time, it was a 9th-magnitude object located within the constellation Ophiuchus,^[b] where he noted that the comet was probably moving towards the northwest.^[4] His discovery was verified by David H. Levy the following night.^[1]

Follow-up observations

Bright moonlight conditions in December 1988 made the observations and orbital calculations of this comet difficult for astronomers. The only known observations made during this time period were conducted by Gary W. Kronk and Alan Hale, who measured the comet's apparent magnitude as 9.1 and 9.4 respectively.^[4] A few days later, while searching for C/1988 Y1, Yanaka discovered his second comet, C/1989 A1, on 1 January 1989.^[8]

M. Tsumura made the last known observations of the comet on 27 February 1989, where it was a 15th-magnitude object within the constellation Canis Major.^[c]

Orbit

Brian G. Marsden published the first parabolic orbital elements for the comet on 4 January 1989 based on 8 known observations at the time.^[9] Additional parabolic orbits published in 8 January, 26 January, and 22 March all revealed that the comet reached perihelion on 11 December 1988 at a distance of 0.43 AU (64 million km) from the Sun.^[10][11]

No further orbital calculations were published until 2017, when Gary W. Kronk used all 36 observations from 1 January to 27 February 1989 and determined a hyperbolic trajectory with an eccentricity of 1.000187.^[4]

Physical characteristics

Measurements of its chemical composition showed that while the comet showed emissions of OI and NH
₂ compounds, it did not display any hints of C
₂ or CN emission by a factor of 100 and 25 respectively.^[6] These unusually low production rates in C
₂ and CN emissions were either likely the consequences for being a dynamically new comet entering the inner Solar System for the first time,^[12] or it may have even formed from an interstellar cloud with a composition entirely different from the nebula that eventually formed the Solar System.^[6]