2018 AH
{{Short description|Near-Earth asteroid Christmas 2021}}
{{Use dmy dates|date=February 2018}}
{{Infobox planet
| minorplanet = yes
| name = 2018 AH
| background = #FFC2E0
| image = 2018AH-orbit.png
| caption = Orbital diagram of {{mp|2018 AH}} with the planets of the inner Solar System
| mpc_name = 2018 AH
| discoverer = ATLAS–MLO
| discovery_site = Mauna Loa Obs.
| discovered = 4 January 2018
{{small|(first observed only)}}
| mp_category = NEO{{·}}Apollo
| epoch = 2022-Jan-21 (JD 2459600.5)
| uncertainty = 0
| observation_arc = 4.01 years
| aphelion = 4.1154 AU
| perihelion = 0.91547 AU
| time_periastron = 2021-Dec-03
| semimajor = 2.5155 AU
| eccentricity = 0.63606
| period = 3.99 yr (1,457 days)
| mean_anomaly = 11.96°
| mean_motion = {{Deg2DMS|0.2474|sup=ms}} / day
| inclination = 12.429°
| asc_node = 101.2°
| arg_peri = 322.9°
| moid = {{convert|0.0065|AU|LD|abbr=on}}
| mean_diameter = 80–170 meters {{small|(2022)}}
84–190 m {{small|(assumed)}}
| rotation =
| albedo = 0.05–0.25 {{small|(assumed)}}
| spectral_type =
| magnitude = ~13 {{small|(peak 2018-01-03)}}
}}
2018 AH is a sub-kilometer asteroid, classified as near-Earth object of the Apollo group, approximately {{convert|100|m|ft|abbr=on|sigfig=1|sp=us}} in diameter. It was first observed on 4 January 2018, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on Mauna Loa and quickly followed-up by many other surveys, with precovery observations found from Pan-STARRS and PTF from the day previous.
It is the largest known asteroid to pass so close to Earth ({{convert|0.001985|AU|km mi|abbr=on|lk=on}}) since {{mpl|2002 JE|9}} in 1971, and until {{mpl-|153814|2001 WN|5}} in 2028, although it was only discovered two days after its closest approach on 2 January 2018, at 04:25 UTC. The Tunguska asteroid was likely of a similar size, if not slightly smaller.
Before being recovered on 4 January 2022 11:49 UTC at an Earth distance of 9.8 million km, the asteroid only had an observation arc of 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. As it came to perihelion on 3 December 2021, it was approaching from the direction of the Sun.
| class="wikitable" style="text-align:center; font-size: 0.9em;"
|+2021 close approach ! Date ! JPL SBDB ! uncertainty | ||
| 2021-12-27.7 ± 3.6 days (as known before recovery) | 4.5 million km | ± 3.6 million km |
| 2021-12-27.548 (as known after recovery) | 4.68 million km | ± 83 km |
Description
{{mp|2018 AH}} has 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 than magnitude 23, 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 =
On its approach to Earth in 2018, {{mp|2018 AH}} had recently passed perihelion and 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. {{mp|2018 AH}} remained brighter than magnitude 23 until late February 2018, and once more became mostly unobservable until its next Earth approach in December 2021.
{{mp|2018 AH}} passed unusually close for such a bright asteroid, at an absolute magnitude of 22.5 (making it approximately 84–190 meters across). 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 than {{mp|2018 AH}} known to pass closer than it to Earth are listed below:
Asteroid diameters marked in italics have had their size directly measured.
| class="wikitable sortable" style="font-size: 0.9em;"
! width=130 | Designation ! width=90 | Date ! Distance ! width=60 | H ! Diameter | ||||
| Tunguska asteroid | 1908-06-30 | {{sort|0|Impact}} | {{sort|23|~23?}} | 60–190 |
| {{mpl|(152680) 1998 KJ|9}} | 1914-12-31 | 232.9 | 19.4 | 279–900 |
| {{mpl|2002 JE|9}} | 1971-04-11 | 237.0 | 21.2 | 122–393 |
| bgcolor=#edf3fe
| 2018 AH | 2018-01-02 | 297.0 | 22.5 | 84–190 |
| {{mpl|(153814) 2001 WN|5}} | 2028-06-26 | 248.7 | 18.3 | 921–943 |
| 99942 Apophis | 2029-04-13 | {{sort|037.8|37.8}} | 19.7 | 310–340 |
| {{mpl|(308635) 2005 YU|55}} | 2075-11-08 | 228.1 | 21.9 | 320–400 |
| {{mpl|(456938) 2007 YV|56}} | 2101-01-02 | 238.8 | 21.0 | 133–431 |
| {{mpl|(153201) 2000 WO|107}} | 2140-12-01 | 243.6 | 19.3 | 427–593 |
| {{mpl|(85640) 1998 OX|4}} | 2148-01-22 | 296.2 | 21.1 | 127–411 |
| class="wikitable collapsible collapsed sortable"
|+{{nowrap|H < 23 asteroids passing less than 1 LD from Earth}} !Asteroid !Date !Nominal approach distance (LD) !Min. distance (LD) !Max. distance (LD) !Absolute magnitude (H) !Size (meters) | ||||||
| bgcolor=#c2c2c2
|{{mpl|(152680) 1998 KJ|9}} | 1914-12-31 | 0.606 | 0.604 | 0.608 | 19.4 | 279–900 |
| bgcolor=#c2c2c2
|{{mpl|(458732) 2011 MD|5}} | 1918-09-17 | 0.911 | 0.909 | 0.913 | 17.9 | 556–1795 |
| bgcolor=#c2c2c2
|{{mpl|(163132) 2002 CU|11}} | 1925-08-30 | 0.903 | 0.901 | 0.905 | 18.5 | 443–477 |
| bgcolor=#c2c2c2
|{{mpl|2002 JE|9}} | 1971-04-11 | 0.616 | 0.587 | 0.651 | 21.2 | 122–393 |
| bgcolor=#c2c2c2
|{{mpl|2013 UG|1}} | 1976-10-17 | 0.854 | 0.853 | 0.855 | 22.3 | 73–237 |
| bgcolor=#c2c2c2
|{{mpl|2012 TY|52}} | 1981-11-04 | 0.818 | 0.813 | 0.823 | 21.4 | 111–358 |
| bgcolor=#c2c2c2
|{{mpl|2017 VW|13}} | 2001-11-08 | 0.454 | 0.318 | 3.436 | 20.7 | 153–494 |
| {{mpl|(308635) 2005 YU|55}} | 2011-11-08 | 0.845 | 0.845 | 0.845 | 21.9 | 320–400 |
| 2018 AH | 2018-01-02 | 0.773 | 0.772 | 0.773 | 22.5 | 67–216 |
| bgcolor=#e2e2e2
|{{mpl|(153814) 2001 WN|5}} | 2028-06-26 | 0.647 | 0.647 | 0.647 | 18.2 | 921–943 |
| bgcolor=#e2e2e2 | 2029-04-13 | 0.0981 | 0.0963 | 0.1000 | 19.7 | 310–340 |
| bgcolor=#e2e2e2
|{{mpl|2015 XJ|351}} | 2047-06-06 | 0.789 | 0.251 | 38.135 | 22.4 | 70–226 |
| bgcolor=#e2e2e2
|{{mpl|2005 WY|55}} | 2065-05-28 | 0.865 | 0.856 | 0.874 | 20.7 | 153–494 |
| bgcolor=#e2e2e2
|{{mp|(308635) 2005 YU|55}} | 2075-11-08 | 0.592 | 0.499 | 0.752 | 21.9 | 320–400 |
| bgcolor=#e2e2e2
|{{mpl|(456938) 2007 YV|56}} | 2101-01-02 | 0.621 | 0.615 | 0.628 | 21.0 | 133–431 |
| bgcolor=#e2e2e2
|{{mpl|2007 UW|1}} | 2129-10-19 | 0.239 | 0.155 | 0.381 | 22.7 | 61–197 |
| bgcolor=#e2e2e2 | 2135-09-25 | 0.780 | 0.308 | 1.406 | 20.19 | 472–512 |
| bgcolor=#e2e2e2
|{{mpl|(153201) 2000 WO|107}} | 2140-12-01 | 0.634 | 0.631 | 0.637 | 19.3 | 427–593 |
| bgcolor=#e2e2e2
|{{mpl|2009 DO|111}} | 2146-03-23 | 0.896 | 0.744 | 1.288 | 22.8 | 58–188 |
| bgcolor=#e2e2e2
|{{mpl|(85640) 1998 OX|4}} | 2148-01-22 | 0.771 | 0.770 | 0.771 | 21.1 | 127–411 |
| bgcolor=#e2e2e2
|{{mpl|2007 UY|1}} | 2156-02-13 | 0.685 | 0.652 | 6.856 | 22.9 | 56–179 |
| bgcolor=#e2e2e2
|{{mpl|2011 LT|17}} | 2156-12-16 | 0.998 | 0.955 | 1.215 | 21.6 | 101–327 |
See also
- {{mpl|2020 AP|1}} – Short arc object (not recently observed) approaching in January 2022
- {{mpl|2009 JF|1}} – Short arc object (not recently observed) possibly approaching in May 2022
- List of asteroid close approaches to Earth in 2018
References
{{reflist|refs=
|type = 2018-02-18 last obs.
|title = JPL Small-Body Database Browser: (2018 AH)
|url = https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=3796295&view=OPC
|publisher = Jet Propulsion Laboratory
|accessdate = 24 December 2021}}
|title = 2018 AH
|work = Minor Planet Center
|url = https://www.minorplanetcenter.net/db_search/show_object?object_id=2018+AH
|accessdate = 22 February 2018}}
|title = Asteroid Size Estimator
|publisher = CNEOS NASA/JPL
|url = https://cneos.jpl.nasa.gov/tools/ast_size_est.html
|accessdate = 5 January 2022}}
|title = Large asteroid 2018 AH flew past Earth at 0.77 LD, 2 days before discovery
|date = 8 January 2018
|work = The Watchers – Daily news service {{!}} Watchers.NEWS
|agency = The Watchers
|url = https://watchers.news/2018/01/08/asteroid-2018-ah/
|accessdate = 22 February 2018}}
|title=Horizons Batch for 2021-Dec-27 13:09 UT
|publisher=JPL Horizons
|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272018+AH%27&START_TIME=%272021-Dec-27%2013:09%27&STOP_TIME=%272021-Dec-28%27&STEP_SIZE=%271+day%27&QUANTITIES=%2720,39%27
|archive-url=https://web.archive.org/web/20211202183004/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272018+AH%27&START_TIME=%272021-Dec-27+16%3A27%27&STOP_TIME=%272021-Dec-28%27&STEP_SIZE=%271+day%27&QUANTITIES=%2720%2C39%27
|archive-date=2021-12-02
|url-status=live
|accessdate=2021-12-02}}
|title = MPEC 2022-A26 : 2018 AH
|date = 2022-01-05
|work = Minor Planet Center
|url = https://minorplanetcenter.net/mpec/K22/K22A26.html
|accessdate = 2022-01-05}}
}}
External links
- [https://minorplanetcenter.net//mpec/K18/K18A23.html MPEC 2018-A23 : 2018 AH], Minor Planet Electronic Circular, 6 January 2018
- [https://twitter.com/minorplanetctr/status/949790577331261441?lang=en Tweet about asteroid 2018 AH], Minor Planet Center
- {{NeoDys|2018AH}}
- {{JPL small body|id=3796295}}
{{2018 in space}}
{{2021 in space}}
{{Small Solar System bodies}}
{{Authority control}}
{{DEFAULTSORT:2018 AH}}