Asteroid 2015 XA378 passes the Earth.

Asteroid 2015 XA378 passed by the Earth at a distance of 3 857 000 km (10.0times the average distance between the Earth and the Moon, or 3.40% of the average distance between the Earth and the Sun), slightly after 7.15 pm GMT on Saturday 19 December 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2015 XA378 has an estimated equivalent diameter of 14-43 m (i.e. it is estimated that a spherical object with the same volume would be 14-43  m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 28 and 10 km above the ground, with only fragmentary material reaching the Earth's surface.

 The calculated orbit of 2015 XA378. JPL Small Body Database.

2015 XA378 was discovered on 13 December 2015 (six days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2015 XA378 implies that it was the 9451st asteroid (asteroid A378) discovered in the first half of December  2015 (period 2015 X).

2015 XA378 has a 910 day orbital period and an eccentric orbit tilted at an angle of 0.23° to the plane of the Solar System that takes it from 0.65 AU from the Sun (i.e. 65% of the average distance at which the Earth orbits the Sun and slightly less than the distance at which the planet Venus orbits the Sun) to 3.02 AU from the Sun (i.e. 302% of the average distance at which the Earth orbits the Sun, slightly more than twice the 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...

Asteroid 2015 XE1 passes the Earth.      Asteroid 2015 XE1 passed by the Earth at a distance of 5 080 000 km (13.2 times the average distance between the Earth and the Moon, or 3.40% of the average distance between the Earth and the Sun), slightly before 3.00 am GMT on Saturday 19 December 2015...

Asteroid 2015 XX169 passes the Earth.  Asteroid 2015 XX169 passed by the Earth at a distance of 3 231 000 km (8.41 times the average distance between the Earth and the Moon, or 2.16% of the average distance between the Earth and the Sun), slightly after 3.00 pm GMT on Monday 14...

Asteroid 2015 XA169 passes the Earth. Asteroid 2015 XA169 passed by the Earth at a distance of 2 848 000 km (7.41 times the average distance between the Earth and the Moon, or 1.90% of the average distance between the Earth and the Sun), slightly before 3.00 pm GMT on Saturday 12...

  

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