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2018 AH

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2018 AH
Orbital diagram of2018 AHwith the planets of theinner Solar System
Discovery[1]
Discovered byATLAS–MLO
Discovery siteMauna Loa Obs.
Discovery date4 January 2018
(first observed only)
Designations
2018 AH
NEO·Apollo[1][2]
Orbital characteristics[2]
Epoch2022-Jan-21 (JD2459600.5)
Uncertainty parameter0
Observation arc4.01 years
Aphelion4.1154AU
Perihelion0.91547 AU
2.5155 AU
Eccentricity0.63606
3.99yr(1,457 days)
11.96°
0° 14m50.64s/ day
Inclination12.429°
101.2°
2021-Dec-03
322.9°
EarthMOID0.0065 AU (2.5 LD)
Physical characteristics
80–170meters(2022)[3]
84–190 m(assumed)[4]
0.05–0.25(assumed)
~13(peak 2018-01-03)
22.7[1]

2018 AHis a sub-kilometerasteroid,classified asnear-Earth objectof theApollo group,approximately 100 m (300 ft) in diameter. It was first observed on 4 January 2018, by theAsteroid Terrestrial-impact Last Alert System(ATLAS) onMauna Loaand quickly followed-up by many other surveys, withprecoveryobservations found fromPan-STARRSandPTFfrom the day previous.

It is the largest known asteroid to pass so close to Earth (0.001985AU(297,000km;184,500mi)) since2002 JE9in 1971,[4]and until2001 WN5in 2028, although it was only discovered two days after its closest approach on 2 January 2018, at 04:25 UTC. TheTunguska asteroidwas likely of a similar size, if not slightly smaller.

Before being recovered on 4 January 2022 11:49 UTC[5]at an Earth distance of 9.8 million km, the asteroid only had anobservation arcof 46 days and had not been observed since February 2018. Being a short arc object that had not been observed for years generated an uncertainty that is relatively large. Between 24–31 December 2021 it was only known to make an Earth approach of between 1-8 million km.[6]As it came to perihelion on 3 December 2021, it was approaching from the direction of the Sun.

2021 close approach
Date JPL SBDB
nominalgeocentric
distance 		uncertainty
region
(3-sigma)
2021-12-27.7 ± 3.6 days
(as known before recovery)		 4.5 million km ± 3.6 million km[6]
2021-12-27.548
(as known after recovery)		 4.68 million km ± 83 km[6]

Description

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2018 AHhas a fairly eccentric orbit, and its distance to the Sun therefore varies from as close as 90% of the Sun-Earth distance to over 4 times that distance. Due to this, among other factors, the asteroid remained undiscovered until its 2018 approach. It is almost always dimmer thanmagnitude23, dimmer than most asteroid surveys can detect. During August–October 2013 it approached within ~0.3 AU of Earth and became as bright as magnitude 22.4, still rather dimmer than most survey-discovered asteroids, and it was not noticed.

2018 Approach

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On its approach to Earth in 2018,2018 AHhad recently passedperihelionand was moving outwards on its orbit. It therefore approached from roughly the direction of the Sun, where it was undetectable to ground-based optical observations. It reached its closest point to Earth at only 45 degrees from the Sun. It was discovered at a more observable elongation of 129 degrees and at a magnitude of 15.7, and was quickly followed up over the next several days due to its brightness.2018 AHremained brighter than magnitude 23 until late February 2018, and once more became mostly unobservable until its next Earth approach in December 2021.

2018 AHpassed unusually close for such a bright asteroid, at anabsolute magnitudeof 22.5 (making it approximately 84–190 meters across).[4]The largest asteroid to pass so close to Earth in 2017 was only an absolute magnitude of 24.3 (or about 31–91 meters). Since 1900, the only asteroids larger than2018 AHknown to pass closer than it to Earth are listed below:

Asteroid diameters marked initalicshave had their size directly measured.

Designation Date Distance
(thousand km) 		H Diameter
(meters)
Tunguska asteroid 1908-06-30 Impact ~23? 60–190
(152680) 1998 KJ9 1914-12-31 232.9 19.4 279–900
2002 JE9 1971-04-11 237.0 21.2 122–393
2018 AH 2018-01-02 297.0 22.5 84–190
(153814) 2001 WN5 2028-06-26 248.7 18.3 921–943
99942 Apophis 2029-04-13 37.8 19.7 310–340
(308635) 2005 YU55 2075-11-08 228.1 21.9 320–400
(456938) 2007 YV56 2101-01-02 238.8 21.0 133–431
(153201) 2000 WO107 2140-12-01 243.6 19.3 427–593
(85640) 1998 OX4 2148-01-22 296.2 21.1 127–411

See also

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References

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  1. ^abc"2018 AH".Minor Planet Center.Retrieved22 February2018.
  2. ^ab"JPL Small-Body Database Browser: (2018 AH)"(2018-02-18 last obs.).Jet Propulsion Laboratory.Retrieved24 December2021.
  3. ^"Asteroid Size Estimator".CNEOS NASA/JPL.Retrieved5 January2022.
  4. ^abc"Large asteroid 2018 AH flew past Earth at 0.77 LD, 2 days before discovery".The Watchers – Daily news service | Watchers.NEWS.The Watchers. 8 January 2018.Retrieved22 February2018.
  5. ^"MPEC 2022-A26: 2018 AH".Minor Planet Center.5 January 2022.Retrieved5 January2022.
  6. ^abc"Horizons Batch for 2021-Dec-27 13:09 UT".JPL Horizons.Archivedfrom the original on 2 December 2021.Retrieved2 December2021.
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