Asteroid 2017 DB passed by the Earth at a distance of 700 400 km (1.82 times the average distance between the Earth and the Moon, 0.47% of the average distance between the Earth and the Sun), slightly before 4.35 pm GMT on Monday 20 February 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 DB has an estimated equivalent diameter of 7-24 m (i.e. it is estimated that a spherical object with the same volume would be 7-24 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 37 and 20 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2017 DB. Minor Planet Center.
2017 DB was discovered on 16 February 2017 (four days before 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 2017 DB implies that the asteroid was the second object (object B) discovered in the second half of February 2017 (period 2017 D).
2017 DB has a 453 day orbital period and an eccentric orbit tilted at an angle of 7.01° to the plane of the Solar System, which takes it from 0.86 AU from the Sun (i.e. 86% of he average distance at which the Earth orbits the Sun) to 1.44 AU from the Sun (i.e. 1.44% of the average distance at which the Earth orbits the Sun, slightly inside the orbit of 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). This means that close encounters between the asteroid and Earth are common, with the last having occurred in August 2012 and the next predicted in September this year.
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