Asteroid 2015 PT227 passed by the Earth at a distance of 3 710 000 km (9.65 times the average distance between the Earth and the Moon, or 2.48% of the average distance between the Earth and the Sun), slightly before 4.05 pm GMT on Saturday 29 August 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2015 PT227 has an estimated equivalent diameter of 31-99 m (i.e. a spherical body with the same mass would be 31-99 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 38 megatons (about 2235 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater over a kilometer across, and resulting in global climatic problems that could last for years or even decades.
The calculated orbit of 2015 PT227. JPL Small Body Database.
2015 PT227 was discovered on 12 August 2015 (17 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2015 PT227 implies that it was the 5694th asteroid (asteroid T227) discovered in the first half of August 2015 (period 2015 P).
2015 PT227 has a 1358 day orbital period and an eccentric orbit tilted at an angle of 1.40° to the plane of the Solar System, which takes it from 0.98 AU from the Sun (i.e. 98% of the average distance at which the Earth orbits the Sun) to 3.82 AU from the Sun (i.e. 382% of the average distance at which the Earth orbits the Sun, and considerably more than twice the average distance at which Mars 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).
See also...
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