Asteroid 2015 FC117 passed by the Earth at a distance of 6 542 000 km (17.0 times the average distance between the Earth and the Moon, or 4.37% of the average distance between the Earth and the Sun), slightly 6.45 am GMT on Sunday 22 March 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2015 FC117 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 27 and 10 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2015 FC117. JPL Small Body Database.
2015 FC117 was discovered on 24 March 2015 (two days after 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 FC117 implies that it was the 2928th asteroid (asteroid C117) discovered in the second half of March 2015 (period 2015 F).
2015 FC117 has an 679 day orbital period and an eccentric orbit tilted at an angle of 25.3° to the plane of the Solar System, which takes it from 0.95 AU from the Sun (i.e. 95% of the average distance at which the Earth orbits the Sun) to 2.08 AU from the Sun (i.e. 208% of the average distance at which the Earth orbits the Sun, considerably greater than the distance 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 2015 FC117 and the Earth are quite common, with the last calculated to have happened in November 2014.
See also...
Asteroid 2015 EG7 passed by the Earth at a distance of 1 044 000 km (2.72 times the average distance between the Earth and the Moon, or 6.98% of the average distance between the Earth and the Sun), slightly before 9.30 pm GMT on Friday 20 March 2015...
Asteroid 2015 FF passed by the Earth at a distance of 1 596 000 km (4.15 times the average distance between the Earth and the Moon, or 10.7% of the average distance between the Earth and the Sun), slightly before 8.30 pm GMT on Friday 20 March 2015...
Asteroid 2015 FE passed by the Earth at a distance of 12 010 000 km (31.3 times the average distance between the Earth and the Moon, or 8.03% of the average distance between the Earth and the Sun), at about 4.45 pm GMT on Thursday 19 March 2015...
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