Thursday 30 July 2020

Asteroid 2006 TU7 passes the Earth.

Asteroid 2006 TU7 passed by the Earth at a distance of about 16 052 000 km (41.8 times the average distance between the Earth and the Moon, or 10.7% of the distance between the Earth and the Sun), slightly after 4.45 pm GMT on Thursday 23 July 2020. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2006 TU7 has an estimated equivalent diameter of 78-250 m (i.e. it is estimated that a spherical object with the same volume would be 78-250 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 350 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater roughly 15 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.

The orbit of 2006 TU6, and its current position. JPL Small Body Database.

2006 TU7 was discovered on 12 October 2012 at Siding Spring Observatory in Australia. The designation 2006 TU7 implies that it was the 164th asteroid (asteroid U6 - 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 U6 = 20 + (24 X 6) = 164) discovered in the first half of October 2006 (period 2006 T).

2006 TU7 has a 287 day (0.78) orbital period, with an elliptical orbit tilted at an angle of 2.92° to the plain of the Solar System which takes in to 0.45 AU from the Sun (45% of the distance at which the Earth orbits the Sun, and slightly outside the distance at which Mercury orbits the Sun) and out to 1.25 AU (25% 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 October 2017 and the next predicted in October 2021. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2006 TU7 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, 2006 TU7 is also classified as a Potentially Hazardous Asteroid.

2006 TU7 also has occasional close encounters with the planets Mercury, which it last came close to in January 2918 and is next predicted to pass in February 2021, and Venus, which it last came close to on 8 Jubethis years (2020) and is expected to pass again in February 2028. 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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