C/2018 C2 (Lemmon)

For other comets discovered by the Mount Lemmon Survey, see Comet Lemmon.

C/2018 C2 (Lemmon) is a hyperbolic comet (previously classified as A/2018 C2, a hyperbolic asteroid). It was first observed on 5 February 2018 by the Mount Lemmon Survey conducted at the Mount Lemmon Observatory near Tucson, Arizona, in the United States.^[1] The discovery was announced on 4 March 2018 along with another hyperbolic object, A/2017 U7.^[2] Based on the absolute magnitude of 15.1, it may measure several kilometers in diameter.^[5] On 22 March 2018 it was determined to be a hyperbolic comet.^[6]

C/2018 C2 (Lemmon)

Annual motion through the Solar System
Discovery [1][2]
Discovered by	Mount Lemmon Srvy.
Discovery site	Mount Lemmon Obs.
Discovery date	5 February 2018 (first observed only)
Designations
MPC designation	C/2018 C2 (Lemmon)
Alternative designations	ZC82561, A/2018 C2
Minor planet category	hyperbolic comet [3]
Orbital characteristics [3]
Epoch 20 May 2018 (JD 2458258.5)
Observation arc	272 days
Perihelion	1.9565 AU
Semi-major axis	−1083±3 AU[a]
Eccentricity	1.0018 0.99924 (Barycentric epoch 2200)[4]
Orbital period (sidereal)	≈ 130,000 years (outbound)[4]
Mean anomaly	-0.00036
Mean motion	0° 0m 0.072s / day
Inclination	34.453°
Longitude of ascending node	91.14°
Argument of perihelion	134.14°
Earth MOID	1.062 AU
Jupiter MOID	1.405 AU
Physical characteristics
Dimensions	1.7–7.6 km (assumed)
Apparent magnitude	19.0 (March 2018)
Absolute magnitude (H)	15.1±0.63

Orbit

Heliocentric eccentricity from 2000–2035 which is strongly influenced by Jupiter's 12 year orbital period.

The path of C/2018 C2 across the sky with annual retrograde loops

While near perihelion, A/2018 C2's heliocentric orbit is not bound to the Solar System, unlike ʻOumuamua, it is not an interstellar object. The heliocentric eccentricity drops below 1 starting with an epoch of January 2023,^[7] when it is 13.8 AU from the Sun, making the orbit bound to the Sun before it leaves the planetary region of the Solar System. The more stable barycentric orbit of A/2018 C2, shows that it is only a very distant small Solar System body, approaching as far as 50,000 AU from the Sun, around the distance of the Oort Cloud. It had an orbital period of millions of years until the current approach to the Solar System, where perturbations will shorten the orbit drastically to about 5,200 AU, with an orbital period of 130,000 years.^[4] Hui Man-To calculated that the comet would have its next perihelion after 130 to 140 thousands years, at a distance of about 2 AU.^[8][4]

As of March 2018^[update], A/2018 C2 was inbound 2.2 AU (330,000,000 km; 200,000,000 mi) from the Sun.^[2] A/2018 C2 made closest approach to the Sun on 2 June 2018 at a distance of 1.9 AU (outside the orbit of Mars).^[3] Since this object out gassed generating a cometary coma^[8] while near the inner Solar System, it was reclassified as a hyperbolic comet.^[9]

Notes

1. Objects on hyperbolic trajectories have negative semimajor axis, giving them a positive orbital energy.