Asteroid 2006 UF17 passed by the Earth at a distance of about 18 027 000 km (46.9 times the average distance between the Earth and the Moon, or 12.0% of the distance between the Earth and the Sun), slightly after 0.30 am GMT on Friday 30 March 2018. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2006 UF17 has an estimated equivalent diameter of 90-280 m (i.e. it is estimated that a spherical object with the same volume would be 90-280 m in diameter), and an object at the upper end of this range 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 about 60 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater overt 4 km in diameter and devastation on a global scale, as well as climatic effects that would last years or even decades.
The calculated orbit of 2006 UF17 Minor Planet Center.
2006 UF17 was discovered on 19 October 2006 by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2006 UF17 implies that it was the 431st asteroid (asteroid F17) discovered in the second half of October 2006 (period 2006 U)
2006 UF17 has a 1424 day orbital period and an eccentric orbit tilted at an angle of 3.73° to the plane of the Solar System, which takes it from 0.37 AU from the Sun (i.e. 37% of he average distance at which the Earth orbits the Sun, slightly less the distance at which the planet Mercury orbits the Sun) to 4.49 AU from the Sun (i.e. 4.49% of the average distance at which the Earth orbits the Sun, and almost three 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). This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in October 2006 and the next predicted in November 2041. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2006 UF17 is also classified as a Potentially Hazardous Asteroid.
2006 UF17 also has frequent close encounters with the planets Mercury, which it is thought to have last passed in June 2014, and is next predicted to pass in November 2027, and Venus, which it last came close to in June 2010 and is next predicted to pass in March 2022). Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.
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