Asteroid 2019 OM1 passed by the Earth at a distance of about 9 890 000 km (25.7 times the average distance between the Earth and the Moon, or 6.61% of the distance between the Earth and the Sun), slightly after 12.30 pm GMT on Monday 19 August 2019. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2019 OM1 has an estimated equivalent diameter of 100-330 m (i.e. it is estimated that a spherical object with the same volume would be 100-330 m in diameter), and an object at the upper end of this range would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be about 88 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater over 5 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.
2019 OM1 was discovered on 25 July 2019 (25 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope. The designation 2019 OM1 implies that it was the 36th asteroid (asteroid M1 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc., which means that M1 = 12 + (24 X 1) = 36) discovered in the second half of July 2019 (period 2019 O).
2019 OM1 has an 955 day orbital period and an eccentric orbit tilted at an angle of 6.16° to the plane of the Solar System, which takes it from 0.76 AU from the Sun (i.e. 76% of he average distance at which the Earth orbits the Sun) to 3.03 AU from the Sun (i.e. 3.03% of the average distance at which the Earth orbits the Sun, which is slightly more than twice the distance at which the planet Mars orbits). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that close encounters between the asteroid and Earth are common, with the last having occurred in January 2012 and the next predicted in October 2022. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2019 OM1 is also classified as a Potentially Hazardous Asteroid.
2010 OM1 also has frequent close encounters with the planets Venus, which it last came close to in July 2014 and is next predicted to pass in December 2024, and Mars, which it is predicted to pass again in April 2025. Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.
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