Asteroid 2017 RJ2 passed by the Earth at a distance of about 550 500 km (1.45 times the average distance between the Earth and the Moon, or 0.37% of the distance between the Earth and the Sun), slightly before 10.30 pm GMT on Friday 15 September 2017. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2017 RJ2 has an estimated equivalent diameter of 5-18 m (i.e. it is estimated that a spherical object with the same volume would be 5-18 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 40 and 26 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2017 RJ2 Minor Planet Center.
2017 RJ2 was discovered on 12 September 2017 (three days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 RJ2 implies that it was the 59th asteroid (asteroid J2) discovered in the first half of September 2017 (period 2017 R).
2017 RJ2 has a 993 day orbital period and an eccentric orbit tilted at an angle of 1.49° to the plane of the Solar System, which takes it from 0.74 AU from the Sun (i.e. 74% of he average distance at which the Earth orbits the Sun, slightly outside the distance at which the planet Venus orbits the Sun) to 3.16 AU from the Sun (i.e. 316% of the average distance at which the Earth orbits the Sun, and more than two times as distant from the Sun than the planet Mars). 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).
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