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2018 XB₄
	Orbit of 2018 XB4 with 15-day motion shown
Discovery
Discovered by	Pan-STARRS
Discovery site	Haleakala Obs.
Discovery date	13 December 2018; (first observed only)
Designations
MPC designation	2018 XB4
Minor planet category	Apollo · NEO
Orbital characteristics
	Epoch 27 April 2019 (JD 2458600.5)
	Uncertainty parameter 5 · 6
Observation arc	42 days
Aphelion	1.2848 AU
Perihelion	0.8577 AU
Semi-major axis	1.0712 AU
Eccentricity	0.1993
Orbital period (sidereal)	1.11 yr (405 d)
Mean anomaly	35.965°
Mean motion	0° 53m 20.4s / day
Inclination	8.7263°
Longitude of ascending node	92.063°
Argument of perihelion	92.282°
Earth MOID	0.0023 AU (0.9 LD)
Jupiter MOID	3.68 AU
Physical characteristics
Mean diameter	53 m
Absolute magnitude (H)	24.0

2018 XB₄ (also written 2018 XB4) is an Apollo near-Earth asteroid roughly 53 meters (170 feet) in diameter. It was discovered on 13 December 2018 when the asteroid was about 0.125 AU (18,700,000 km; 11,600,000 mi) from Earth and had a solar elongation of 146°. It passed closest approach to Earth on 1 January 2019.^[3] Of the asteroids discovered in 2018, it had the highest Palermo scale rating at –3.6. In mid-2019 it was recovered which extended the observation arc to 177 days and was removed from the Sentry Risk Table on 12 June 2019. It is now known that on 22 June 2092 the asteroid will pass about 0.033±0.015 AU from Earth.^[3]

With a 42-day observation arc, the Sentry Risk Table showed an estimated 1 in 6200 chance of the asteroid impacting Earth on 22 June 2092.^[4] The nominal JPL Horizons 22 June 2092 Earth distance was 0.17 AU (25,000,000 km; 16,000,000 mi) with a 3-sigma uncertainty of ±320 million kilometers. A Monte Carlo simulation using Solex 12 with 1000 clones of the asteroid showed that by 2092 the uncertainty region for 2018 XB₄ stretched around the entire orbit.^[5] NEODyS listed the nominal 22 June 2092 Earth distance as 0.009 AU (1,300,000 km; 840,000 mi).^[6]

References

^ "MPEC 2018-X119: 2018 XB4". IAU Minor Planet Center. 15 December 2018. Retrieved 19 February 2019. (K18X04B)
^ ^a ^b ^c ^d "2018 XB4". Minor Planet Center. Retrieved 26 February 2019.
^ ^a ^b ^c ^d ^e ^f "JPL Small-Body Database Browser: (2018 XB4)" (last observation: 2019-01-24; arc: 42 days). Jet Propulsion Laboratory. Archived from the original on 20 February 2019. Retrieved 19 February 2019.
^ ^a ^b "Earth Impact Risk Summary: 2018 XB4". NASA/JPL Near-Earth Object Program Office. Archived from the original on 18 February 2019. Retrieved 20 February 2019.
^ Solex clones (Peter Thomas)
^ "2018XB4 Ephemerides for 22 June 2092". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 20 February 2019. Retrieved 20 February 2019.