2019 OK

2019 OK

2019 OK orbits near the ecliptic plane out to the asteroid belt and inside the orbit of Venus
Discovery[1]
Discovered by	SONEAR Obs.
Discovery site	SONEAR Obs. (Y00)
Discovery date	24 July 2019
Designations
MPC designation	2019 OK
Alternative designations	NEOCP S511618[2]
Minor planet category	Apollo · NEO
Orbital characteristics[3]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 1
Observation arc	2.42 years
Earliest precovery date	2017-02-21 (Pan-STARRS)
Aphelion	3.4315 AU
Perihelion	0.4635 AU
Semi-major axis	1.9475 AU
Eccentricity	0.7620
Orbital period (sidereal)	2.72 yr (993 d)
Mean anomaly	310.58°
Mean motion	0° 21m 45.36s / day
Inclination	1.4006°
Longitude of ascending node	302.27°
Argument of perihelion	104.24°
Earth MOID	0.00036 AU (54,000 km) (0.14 LD)
Physical characteristics
Mean diameter	57–130 m (187–426 ft)
Absolute magnitude (H)	23.3±0.3[3] 23.3[1]

2019 OK^[a] is a near-Earth asteroid noted for its sudden, surprise discovery on the day before it flew by at approximately 70,000 km (43,000 mi) 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 was discovered by the ATLAS survey on 24 July 2019, approximately one day before its closest approach to Earth. Its late detection was primarily due to its approach direction from the daytime sky, close to the Sun as seen from Earth, which significantly reduced its observability by ground-based optical surveys.

Near-Earth objects arriving from solar elongations near 0° are difficult to detect because telescopes conducting asteroid surveys generally avoid regions of the sky close to the Sun due to scattered sunlight and reduced contrast. As a result, 2019 OK was only identified once it had moved into a more favorable observing geometry shortly before its close approach.

The case of 2019 OK has been cited in planetary defense studies as an example of the observational blind spot for asteroids approaching from sunward directions.

2019 OK was first detected on 24 July 2019 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope. Following initial detection, follow-up observations were rapidly conducted by multiple observatories to refine its orbit in the limited time before closest approach.

Within hours of discovery, additional astrometric measurements were reported to the Minor Planet Center, allowing the orbit solution to be improved significantly. As more observations were added, uncertainty in the predicted trajectory decreased, enabling accurate prediction of its Earth flyby on 25 July 2019.

After the close approach, further observations helped extend the observational arc and refine its orbital parameters, improving long-term orbit modeling.

2019 OK is estimated to be approximately 50–130 metres in diameter, based on its absolute magnitude and assumed range of possible surface reflectivities (albedo). The large uncertainty in size arises from the lack of direct radar imaging or spacecraft observations.

No detailed spectral classification or rotation period measurements have been widely published for 2019 OK as of its initial discovery and close-approach campaign. As a result, its composition is inferred only indirectly from typical near-Earth asteroid population characteristics.

The object is considered representative of mid-sized near-Earth asteroids that are primarily studied through optical astrometry rather than direct physical observation.

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 last previous 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 Southern constellation Capricornus and close to 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, it was at that time moving directly towards the observer and its apparent motion across the sky was extremely slow, with a rate of 0.01 degrees/day, and it was not recognized as a moving object.^[7]

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]

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]

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]

If 2019 OK is around 100 m (330 ft) in diameter, an Earth impact could have released as much power as the 50 megatons generated by the Tsar Bomba hydrogen bomb.^[13] If 2019 OK is around the middle of the size estimates, it could instead 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 is on the smaller size it still could have released over 30 times the energy of the atomic blast by Little Boy at Hiroshima.^[14]

• 2020 LD
• Asteroid impact prediction
• List of asteroid close approaches to Earth in 2019
• List of asteroid close approaches to Earth
• List of bolides (asteroids and meteoroids that impacted Earth)

• 2019 OK at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• 2019 OK at the IAU Minor Planet Center
• 2019 OK at the JPL Small-Body Database