2019 OK is a

near-Earth asteroid A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU) ...

noted for its sudden, surprise discovery on the day before its close flyby in 2019. The object's size is estimated at across, the closest asteroid of such size discovered in 2019. It is uncommon for asteroids of this size to pass within of Earth.

Discovery

The first valid detection occurred on 24 July 2019, when it was from Earth and had an apparent magnitude of 14.7. The full moon on 16 July 2019 slowed down the 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 Opposition may refer to: Arts and media * ''Opposition'' (Altars EP), 2011 EP by Christian metalcore band Altars * The Opposition (band), a London post-punk band * '' The Opposition with Jordan Klepper'', a late-night television series on Com ...

(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 The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function ...

'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. 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 Capricornus is one of the constellations of the zodiac. Its name is Latin for "horned goat" or "goat horn" or "having horns like a goat's", and it is commonly represented in the form of a sea goat: a mythical creature that is half goat, half fi ...

and the bright moon. The

Pan-STARRS The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; obs. code: F51 and Pan-STARRS2 obs. code: F52) located at Haleakala Observatory, Hawaii, US, consists of astronomical cameras, telescopes and a computing facility that is ...

1 telescope recorded an image of 2019 OK on 28 June 2019 when it was from Earth and had an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of 22.9. Automatic analysis missed detecting the object in the Pan-STARRS image because the object was too faint. The

1 telescope again saw the object on 7 July 2019 when the object was brighter with magnitude 21.2. However, because it was 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.

Orbit and classification

The asteroid is a member of the

Flora family The Flora family (''adj. Florian''; ; also known as ''Ariadne family'') is a prominent family of stony asteroids located in the inner region of the asteroid belt. It is one of the largest families with more than 13,000 known members, or appro ...

(), a giant

asteroid family An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. A ...

and the largest family of stony asteroids in the main-belt. 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 In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the lo ...

of 1.95 AU). Its orbit has an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off- center, in geometry * Eccentricity (graph theory) of a ...

of 0.76 and an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

of 1 ° with respect to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agai ...

. After evaluating its orbit, the asteroid was identified as the most probable

parent body In meteoritics, a parent body is the celestial body from which originates a meteorite or a class of meteorites. Identification The easiest way to correlate a meteorite with a parent body is when the parent body still exists. This is the case fo ...

of the particles responsible for the

meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extr ...

designated, 17 Capricornids (SCP #1042).

2019 flyby

On 25 July 2019 at 01:22 UTC it had its closest approach to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

, when it passed about —less than one-fifth of the distance to the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...

. Its speed was nearly per hour. On 28 July 2116 the asteroid will pass about from Earth.

Close flybys of larger asteroids

Asteroids in the

Chelyabinsk meteor The Chelyabinsk meteor was a superbolide that entered Earth's atmosphere over the southern Ural region in Russia on 15 February 2013 at about 09:20 YEKT (03:20 UTC). It was caused by an approximately near-Earth asteroid that entered the ...

size range to 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 depends on the objects albedo (how reflective it is).

Potential impact effects

If 2019 OK had been around in diameter an Earth impact could have released as much power as the 50 megatons generated by

Tsar Bomba The Tsar Bomba () (code name: ''Ivan'' or ''Vanya''), also known by the alphanumerical designation "AN602", was a thermonuclear aerial bomb, and the most powerful nuclear weapon ever created and tested. Overall, the Soviet physicist Andrei Sa ...

.Asteroid Danger Explained
(ESA) 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 The Tunguska event (occasionally also called the Tunguska incident) was an approximately 12- megaton explosion that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of June ...

that flattened 2,000 km² (770 square miles) of forest land. 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 "Little Boy" was the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II, making it the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress '' Enola Gay ...

at Hiroshima.The day Earth had a near-miss with a 'city-killer' asteroid.
Liam Mannix, ''The Sydney Herald'' 25 July 2019.

Notelist

References

External links

* * at the ''IAU

'' * {{DEFAULTSORT:2019 OK # Minor planet object articles (unnumbered) 20190725 20190725