C/2011 KP36 (Spacewatch)

C/2011 KP₃₆ (Spacewatch) is a distant long-period comet that completes an orbit once every 238 years around the Sun. With a nucleus diameter of 55.1 km (34.2 mi),^[4] it is one of the largest comets ever discovered.^[2]

C/2011 KP₃₆ (Spacewatch)

Discovery[1]
Discovered by	Spacewatch Terrence H. Bressi
Discovery site	Kitt Peak Observatory
Discovery date	21 May 2011
Designations
Alternative designations	CK11K36P
Orbital characteristics[2]
Epoch	22 June 2016 (JD 2457561.5)
Observation arc	8.83 years
Number of observations	3,711
Aphelion	71.939 AU
Perihelion	4.883 AU
Semi-major axis	38.411 AU
Eccentricity	0.87287
Orbital period	238.07 years
Inclination	18.987°
Longitude of ascending node	173.40°
Argument of periapsis	180.59°
Mean anomaly	0.108°
Last perihelion	26 May 2016
Next perihelion	5 June 2254
TJupiter	2.643
Earth MOID	3.879 AU
Jupiter MOID	0.079 AU
Physical characteristics[2][3]
Mean diameter	55.1 km (34.2 mi)
Geometric albedo	0.101
Spectral type	(B–R) = 1.9±0.3
Comet total magnitude (M1)	7.5
Comet nuclear magnitude (M2)	9.5

Observational history

It was initially thought to be an asteroid-like object with a very eccentric orbit at the time of its discovery on 21 May 2011.^[1] A series of stacked images obtained from observations taken between April and May 2012 showed signs of diffuse cometary activity,^[5] with a coma about 6 arcseconds in diameter and a faint tail about 9 arcseconds in length.^[6][7]

Orbit

Orbital calculations of the comet showed that it has a very eccentric orbit whose perihelion is around 4.88 AU (730 million km) from the Sun and an aphelion of 71.94 AU (10.762 billion km), almost twice that of Neptune.^[3]

NASA / JPL considers this comet as part of the Jupiter-family of comets,^[2] however this is highly unlikely as it takes roughly 238 years to complete one full orbit around the Sun. Some astronomers even consider this comet a scattered disc object,^[8][9] however Dr. Yan R. Fernandez concluded that 2011 KP₃₆ belongs to the “group of long-period comets that are nearly Halley-type” despite its Tisserand parameter being around 2.64.^[3][10]