Asteroid 2015 OV passed by the Earth at a distance of 11 220 000 km (29.2 times the average distance between the Earth and the Moon, or 7.50% of the average distance between the Earth and the Sun), slightly after midday GMT on Monday 24 August 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2015 OV has an estimated equivalent diameter of 38-120 m (i.e. a spherical body with the same mass would be 38-120 m in diameter), and an object towards the upper end of this range would pass through the atmosphere and directly impact the ground with a force of about 80 megatons (about 4700 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater over 1.5 kilometers across, and resulting in global climatic problems that could last for years or even decades.
The calculated orbit of 2015 OV. JPL Small Body Database.
2015 OV was discovered on 19 July 2015 (36 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2015 OV implies that it was the 21st asteroid (asteroid V) discovered in the second half of July 2015 (period 2015 O).
2015 OV has a 435 day orbital period and an eccentric orbit tilted at an angle of 7.65° to the plane of the Solar System, which takes it from 0.94 AU from the Sun (i.e. 94% of the average distance at which the Earth orbits the Sun) to 1.31 AU from the Sun (i.e. 131% of the average distance at which the Earth orbits the Sun). 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 extremely common, with the last having occurred in January 2010 and the next predicted in February 2016.
See also...
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