Asteroid 2017 SR2 passed by the Earth at a distance of about 93 260 km (0.24 times the average distance between the Earth and the Moon, or 0.01% of the distance between the Earth and the Sun), slightly before 8.30 pm GMT on Wednesday 20 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 SR2 has an estimated equivalent diameter of 3-11 m (i.e. it is estimated that a spherical object with the same volume would be 3-11 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 more that 30 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2017 SR2 Minor Planet Center.
2017 SR2 was discovered on 20 September 2017 (the day of its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2017 SR2 implies that it was the 67th asteroid (asteroid R2) discovered in the second half of September 2017 (period 2017 R).
2017 SR2 has a 1223 day orbital period and an eccentric orbit tilted at an angle of 0.6° to the plane of the Solar System, which takes it from 0.95 AU from the Sun (i.e. 95% of he average distance at which the Earth orbits the Sun) to 3.53 AU from the Sun (i.e. 353% of the average distance at which the Earth orbits the Sun, considerably more 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 the asteroid has occasional close encounters with the planet Earth, with the next predicted to occur in August 2020.
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