Asteroid (531060) 2012 DJ61 passed by the Earth at a distance of about 12 192 000 km (31.7 times the average distance between the Earth and the Moon, or 8.15% of the distance between the Earth and the Sun), slightly after 3.00 am GMT on Thursday 5 March 2020. There was no danger of the asteroid hitting us, though were it to do so it would have presented a considerable threat. (531060) 2012 DJ61 has an estimated equivalent diameter of 200-620 m (i.e. it is estimated that a spherical object with the same volume would be 200-620 m in diameter), and an object of this size would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 15 000-600 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 3-8 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.
The calculated orbit of (531060) 2012 DJ61. Minor Planet Center.
(531060) 2012 DJ61 was discovered on 28 February 2012 by the University of Hawaii's PANSTARRS telescope. The designation 2012 DJ61 implies that it was the 1534th asteroid (asteroid J61 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc., which means that J61 = 6 + (24 X 61) = 1534) discovered in the second half of February 2012 (period 2012 D), while the designation 531060 implies that it was 531 060th asteroid ever discovered (asteroids are not given this longer designation immediately to avoid naming double or false sightings).
(531060) 2012 DJ61 has a 321 day orbital period, with an elliptical orbit tilted at an angle of 53.6° to the plain of the Solar System which takes in to 0.44 AU from the Sun (44% of the distance at which the Earth orbits the Sun, and slightly more than the distance at which Mercury orbits the Sun) and out to 1.39 AU (39% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in February 2013 and the next predicted in March 2027. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, (531060) 2012 DJ61 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, (531060) 2012 DJ61 is also classified as a Potentially Hazardous Asteroid. The asteroid also has occasional close encounters with the planet Mercury, with the last having happened in November 1965, and the next predicted for February 1951.
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