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 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 XA169 has an estimated equivalent diameter of 6-20 m (i.e. it is estimated that a spherical object with the same volume would be 6-20 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 38 and 22 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2015 XA169. JPL Small Body Database.
2015 XA169 was discovered on 8 December 2015 (four days beffore its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2015 XA169 implies that the asteroid was the 4226th object (object A169) discovered in the first half of December 2015 (period 2015 X).
2015 XA169 has a 739 day orbital period and an eccentric orbit tilted at an angle of 12.2° to the plane of the Solar System that takes it from 0.94 AU from the Sun (i.e. 94% of the average distance at which the Earth orbits the Sun) to 2.62 AU from the Sun (i.e. 262% of the average distance at which the Earth orbits the Sun, and considerably more than the distance at which the planet Mars orbits). 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 fairly common, with the last thought to have happened in November 2013 this year and the next predicted in December 2017.
See also...
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Asteroid 2015 SV2 passes the Earth. Asteroid 2015 SV2 passed by the Earth at a distance of 14 800 000 km (38.5 times the average distance between the Earth and the Moon, or 9.89% of the average distance between the Earth and the Sun), at about 3.45 pm GMT on Saturday 5 December...
Asteroid 2015 WB13 passes the Earth. Asteroid 2015 WB13 passed by the Earth at a distance of 18 950 000 km (49.3 times the average distance between the Earth and the Moon, or 12.7% of the average distance between the Earth and the Sun), at about 8.55 pm GMT on Thursday 3...Follow Sciency Thoughts on Facebook.
