Asteroid 2010 GT7 passed by the Earth at a distance of about 9 444 000 km (24.6 times the average distance between the Earth and the Moon, or 6.31% of the distance between the Earth and the Sun), slightly before 6.45 am GMT on Monday 24 December 2018. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2010 GT7 has an estimated equivalent diameter of 170-540 m (i.e. it is estimated that a spherical object with the same volume would be 170-540 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 between 6000 and 600 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater between 2.5 and 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 2010 GT7 Minor Planet Center.
2010 GT7 was discovered on 7 April 20108 by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2010 GT7 implies that it was the 194th asteroid (asteroid T7) discovered in the first half of April 2010 (period 2010 G).
2010 GT7 has an 1636 day orbital period and an eccentric orbit tilted at an angle of 9.26° 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 4.57 AU from the Sun (i.e. 457% of the average distance at which the Earth orbits the Sun, and slightly more than three times as far from the Sun as 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 March 2010 and the next predicted in March 2028. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2010 GT7 is also classified as a Potentially Hazardous Asteroid.
2010 GT7 also has frequent close encounters with the planets Mars, which it is next predicted to pass in February 2114, and Jupiter, which it last came close to in September 1985 and is next predicted to pass in February 2025. 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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