Asteroid 2015 BP4 passed by the Earth at a distance of 15 770 000 km (40.96 times the average distance between the Earth and the Moon, or 10.5 % of the average distance between the Earth and the Sun), at about 3.15 am GMT on Wednesday 11 February 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented minor threat. 2015 BP4 has an estimated equivalent diameter of 38-120 m (i.e. it is estimated that a spherical object with the same volume 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 50 megatons (about 3000 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater almost two kilometers across.
The calculated orbit of 2015 BP4. JPL Small Body Database.
2015 BP4 was discovered on 16 January 2015 (27 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2015 BP4 implies that it was the 115th asteroid (asteroid P4) discovered in the second half of January 2015 (period 2015 B).
2015 BP4 has an 567 day orbital period and an eccentric orbit tilted at an angle of 12.7° to the plane of the Solar System, which takes it from 0.80 AU from the Sun (i.e. 80% of the average distance at which the Earth orbits the Sun) to 1.88 AU from the Sun (i.e. 188% of the average distance at which the Earth orbits the Sun, considerably more than the disctance at which the planet 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). This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in August 1959 and the next predicted in July 2018.
See also...
Asteroid 2015 BM510 passed by the Earth at a distance of 5 311 000 km (13.82 times the average distance between the Earth and the Moon, or 3.5 % of the average distance between the Earth and the Sun), slightly after 9.00 pm GMT on Tuesday 10 February...
Asteroid 2013 BS45 passed by the Earth at a distance of 13 380 000 km (34.8 times the average distance between the Earth and the Moon, or 8.9 % of the average distance between the Earth and the Sun), slightly after 11.15 am GMT on Monday 9 February...
Asteroid 2015 CM passed by the Earth at a distance of 3 236 000 km (8.42 times the average distance between the Earth and the Moon, or 2.2 % of the average distance between the Earth and the Sun), slightly before 8.40 am GMT on Monday 9 February...
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