2019 OK

2019 OK[lower-alpha 1] is a near-Earth asteroid noted for its sudden, surprise discovery on the day before its close flyby in 2019.[4] The object's size is estimated at 57 to 130 metres (187 to 426 ft) across, the closest asteroid of such size discovered in 2019.[5] It is uncommon for asteroids of this moderately large size to pass within 100,000 km (62,000 mi) of Earth.

2019 OK
2019 OK orbits near the ecliptic plane out to the asteroid belt and inside the orbit of Venus
Discovery [1]
Discovered bySONEAR Obs.
Discovery siteSONEAR Obs. (Y00)
Discovery date24 July 2019
Designations
2019 OK
NEOCP S511618[2]
Apollo · NEO
Orbital characteristics [3]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 1
Observation arc2.42 years
Earliest precovery date2017-02-21 (Pan-STARRS)
Aphelion3.4315 AU
Perihelion0.4635 AU
1.9475 AU
Eccentricity0.7620
2.72 yr (993 d)
310.58°
0° 21m 45.36s / day
Inclination1.4006°
302.27°
104.24°
Earth MOID0.00036 AU (54,000 km) (0.14 LD)
Physical characteristics
Mean diameter
57–130 m (187–426 ft)
23.3±0.3[3]
23.3[1]

    Discovery

    The first detection made public occurred on 24 July 2019, when it was 0.01 AU (1,500,000 km; 930,000 mi) from Earth and had an apparent magnitude of 14.7.[6] The full moon on 16 July 2019 slowed down the asteroid discovery rate during mid-July. The asteroid was detected by Cristóvão Jacques, Eduardo Pimentel and João Ribeiro at the private SONEAR Observatory in Oliveira, Minas Gerais when it was very close to opposition (opposite the Sun in the sky) with a solar elongation of 170 degrees. About 10 hours later it was independently detected by ASAS-SN project in images from two of its telescopes, which allowed a preliminary determination of its orbit. It was subsequently listed on the Minor Planet Center's Near-Earth Object Confirmation Page (NEOCP) as S511618. The listing was confirmed and publicly announced as 2019 OK with three hours remaining before the 25 July 2019 closest approach.[6]

    Various circumstances prevented an earlier discovery, despite the efforts to continuously hunt for such objects. The earlier appearance was not lost in the glare of the Sun, but was not favorable to survey instruments located in the Northern Hemisphere, due to its celestial direction in the constellation Capricornus and the bright moon. The Pan-STARRS1 telescope did record an image of 2019 OK on 28 June 2019 when it was 0.39 AU (58,000,000 km; 36,000,000 mi) from Earth and had an apparent magnitude of 22.9.[6] Automatic analysis missed detecting the object in the Pan-STARRS image because the object was too faint. The Pan-STARRS1 telescope again saw the object on 7 July 2019 when the object was brighter with magnitude 21.2. However, because it was at that time moving directly towards the observer, its apparent motion was extremely slow, with a rate of 0.01 degrees/day, and it was not recognized as a moving object.[7]

    Orbit and classification

    The asteroid is a member of the Flora family (402), a populous asteroid family and the largest family of stony asteroids in the main-belt.[8] It orbits the Sun in the inner main-belt at a distance of 0.5–3.4 AU once every 2 years and 9 months (993 days; semi-major axis of 1.95 AU). Its orbit has an eccentricity of 0.76 and an inclination of 1° with respect to the ecliptic.[3] After evaluating its orbit, the asteroid was identified as the most probable parent body of the particles responsible for the meteor shower designated, 17 Capricornids (SCP #1042).[9]

    2019 flyby

    On 25 July 2019 at 01:22 UTC it had its closest approach to Earth, when it passed about 0.00047697 AU (71,354 km; 44,337 mi)—less than one-fifth of the distance to the Moon.[3] Its speed was nearly 88,500 kilometres (55,000 mi) per hour.[10][11]

    Animation of 2019 OK's orbit
    Around the Sun
    Around the Earth

       2019 OK  ·   Sun ·   Mercury ·   Venus  ·   Earth  ·   Moon

    On 28 July 2116 the asteroid will pass about 0.03 AU (4,500,000 km; 2,800,000 mi) from Earth.[3]

    Close flybys of larger asteroids
    Asteroids roughly 50+ meters in diameter (H≤24)
    that passed inside 1 lunar distance from 2009 to 2019
    Asteroid Date Distance
    (thousand km)    		 H Diameter
    (meters)
    (albedo=0.15)
    2019 OK2019-07-257123.375
    2019 OD2019-07-2435723.568
    2010 WC92018-05-1520223.665
    2018 GE32018-04-1519223.860
    2018 AH2018-01-0229622.5110
    367943 Duende2013-02-153424.054
    2011 XC22011-12-0334723.279
    (308635) 2005 YU552011-11-0832421.9140

    Asteroids in the 20 m (66 ft) Chelyabinsk meteor size range to 50 m (160 ft) Tunguska size range (absolute magnitude H ~26–24) approach closer than the Moon about once per month. Asteroids with an absolute magnitude of 26–24 will vary in size from 17 to 94 m (56 to 308 ft) depends on the objects albedo (how reflective it is).[12]

    Potential impact effects

    If 2019 OK had been around 100 m (330 ft) in diameter an Earth impact could have released as much power as the 50 megatons generated by Tsar Bomba.[13] If 2019 OK had been around the middle of the size estimates it could have released the equivalent explosive energy of about 10 megatons of TNT similar to the 1908 Tunguska event that flattened 2,000 km2 (770 square miles) of forest land.[11] If 2019 OK had been on the smaller size it still could have released over 30 times the energy of the atomic blast by Little Boy at Hiroshima.[14]

    See also

    Notes
    1. The name 2019 OK is the provisional designation which is based on the date it was discovered. 2019 for the year, "O" for half-month of July 16–31, and "K" for the 10th discovery of the second half of July.

    References
    1. "2019 OK". Minor Planet Center. Retrieved 28 July 2019.
    2. Gray, Bill. "Pseudo-MPEC for 2019 OK = S511618 = asassn3". Project Pluto. Retrieved 1 August 2019.
    3. "JPL Small-Body Database Browser: (2019 OK)" (2019-07-25 last obs.). Jet Propulsion Laboratory. Retrieved 28 July 2019.
    4. Vergano, Dan; Leopold, Jason (19 September 2019). "A "Sneaky" Asteroid Narrowly Missed Earth This Summer. Internal Emails Show How NASA Scientists Totally Missed It. - "This one did sneak up on us," one NASA expert wrote in an internal email, two days after the football-field-sized asteroid narrowly missed the planet". BuzzFeed News. Retrieved 20 September 2019.
    5. Mannix, Liam. "Earth had a near-miss with a 'city-killer' asteroid". stuff.co.nz. Retrieved 26 July 2019.
    6. "MPEC 2019-O56 : 2019 OK". IAU Minor Planet Center. 25 June 2019. Retrieved 31 July 2019. (K19O00K)
    7. Wainscoat, R.; Weryk, R.; Chesley, S.; Vereš, P.; Micheli, M. (February 2022). "Regions of slow apparent motion of close approaching asteroids: The case of 2019 OK". Icarus. Academic Press. 373: 114735. doi:10.1016/J.ICARUS.2021.114735. ISSN 0019-1035.
    8. Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families". Asteroids IV. pp. 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131.
    9. Trindade, L. S.; Dal’Ava Jr., A.; Faria, C. J.; Zurita, M.; Silva, G. G. (May 2021). "Identification of new meteor showers SCP (#1042) and OSG (#1043) and their associations with the asteroids 2019 OK and 2017 NT5" (PDF). EMeteorNews. 6 (4): 297–310. Archived from the original (PDF) on 26 May 2021. Retrieved 30 June 2021.
    10. Haynes, Korey. "A large asteroid just zipped between Earth and the Moon". astronomy.com. Retrieved 26 July 2019.
    11. Chiu, Allyson (26 July 2019). "'It snuck up on us': Scientists stunned by 'city-killer' asteroid that just missed Earth". The Washington Post. Retrieved 27 July 2019.
    12. Asteroid Size Estimator using H=26 albedo=0.25 and H=24 albedo=0.05
    13. Asteroid Danger Explained (ESA)
    14. The day Earth had a near-miss with a 'city-killer' asteroid. Liam Mannix, The Sydney Herald 25 July 2019.

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