Asteroid 2000 BO28 passed by the Earth at a distance of about 10 980 000 km (28.6 times the average distance between the Earth and the Moon, or 7.34% of the distance between the Earth and the Sun), slightly after 3.05 am GMT on Saturday 21 March 2020. There was no danger of the asteroid hitting us, though were it to do so it would have presented a considerable threat. 2000 BO28 has an estimated equivalent diameter of 210-650 m (i.e. it is estimated that a spherical object with the same volume would be 210-650 m in diameter), and an object of this size 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 20 000-825 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 3-10 km in diameter and devastation on a global scale, as well as climatic effects that would last years or even decades.
2000 BO28 was discovered on 30 January 2000 by the University of Arizona's Kitt Peak-Spacewatch Project at the Steward Observatory in the Catalina Mountains north of Tucson. The designation 2000 BO28 implies that it was the 686th asteroid (asteroid O28 - 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 O28 = 14 + (24 X 28) = 686) discovered in the seconf half of January 2000 (period 2000 B).
2000 BO28 has a 809 day (2.21 year) orbital period, with an elliptical orbit tilted at an angle of 6.34° to the plain of the Solar System which takes in to 0.68 AU from the Sun (68% of the distance at which the Earth orbits the Sun, and slightly inside the orbit of the planet Venus) and out to 2.72 AU (272% of the distance at which the Earth orbits the sun and further from the Sun than the planet Mars). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in July 2011 and the next predicted in September 2022. 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). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2000 BO28 is also classified as a Potentially Hazardous Asteroid.
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