Friday 1 September 2017

Asteroid 2017 QQ17 passes the Earth.

Asteroid 2017 QQ17 passed by the Earth at a distance of about 392 500 km (1.02 times the average distance between the Earth and the Moon, or 0.26% of the distance between the Earth and the Sun), slightly before 7.25 am GMT on Saturday 26 August 2017. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2017 QQ17 has an estimated equivalent diameter of 4-13 m (i.e. it is estimated that a spherical object with the same volume would be 4-13 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 43 and 28 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 QQ17 Minor Planet Center.

2017 QQ17 was discovered on 23 August 2017 (three days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 QQ17 implies that it was the 441st asteroid (asteroid Q17) discovered in the second half of August 2017 (period 2017 Q).

2017 QQ17 has a 1415 day orbital period and an eccentric orbit tilted at an angle of 2.27° to the plane of the Solar System, which takes it from 0.61 AU from the Sun (i.e. 61% of he average distance at which the Earth orbits the Sun, inside the distance at which the planet Venus orbits the Sun) to 4.31 AU from the Sun (i.e. 431% of the average distance at which the Earth orbits the Sun, and 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 next predicted in December 2056.  

2017 QQ17 also has frequent close encounters with the planets Mars, which it is thought to have last passed in May 2010, and Jupiter which it last came close to in July 1935, and is next predicted to come close to September 2042. 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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