Saturday 15 June 2019

Asteroid 2011 TC4 passes the Earth.

Asteroid 2011 TC4 passed by the Earth at a distance of about 12 732 000 km (33.1 times the average  distance between the Earth and the Moon, or 8.51% of the distance between the Earth and the Sun), slightly after midnight GMT on Wednesday 12 June 2019. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2011 TC4 has an estimated equivalent diameter of 160-520 m (i.e. it is estimated that a spherical object with the same volume would be 180-570 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 about 6000 and 470 000 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 2018 XG5. JPL Small Body Database.

2011 TC4 was discovered on 3 October 2011 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 2011 TC1 implies that the asteroid was the 27th object (asteroid C1 - 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 C1 = 3 + (24 X 1) = 27)) discovered in the first half of October 2011 (period 2011 T).

2011 TC4 has an 666 day orbital period and an eccentric orbit tilted at an angle of 3.13° to the plane of the Solar System, which takes it from 0.41 AU from the Sun (i.e. 41% of he average distance at which the Earth orbits the Sun, and slightly outside the orbit of the planet Mercury) to 2.57 AU from the Sun (i.e. 257% of the average distance at which the Earth orbits the Sun, and somewhat more than 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 extremely common, with the last having occurred in November 2011 and the next predicted in October 2022. 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 Mercury, which it last came close to in September 2014 and is  next predicted to pass in November 2033, Venus, which it last came close to in June 2001 and is predicted to pass again in December 2033, and Mars, which it last came close to in February 1968 and is next predicted to pass in October 2193. 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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