Sunday 30 April 2017

Asteroid 2017 GK4 passes the Earth.

Asteroid 2017 GK4 passed by the Earth at a distance of about 13 800 000 km (35.9 times the average distance between the Earth and the Moon, or 9.2% of the distance between the Earth and the Sun), slightly after 9.00 am GMT on Sunday 23 April 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a considerable threat. 2017 GK4 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 towards the upper end of this size 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 60 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater about 4 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 2017 GK4. Minor Planet Center.

2017 GK4 was discovered on 1 April 2017 (22 days after its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 GK4 implies that it was the 111th asteroid (asteroid GK4) discovered in the first half of April 2017 (2017 G).

2017 GK4 has a 554 day orbital period and an eccentric orbit tilted at an angle of 16.4° to the plane of the Solar System, which takes it from 0.81 AU from the Sun (i.e. 81% of he average distance at which the Earth orbits the Sun) to 1.82 AU from the Sun (i.e. 182% of the average distance at which the Earth orbits the Sun, and considerably outside 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 April 2014 and the next predicted in May 2020 As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, (474231) 2001 HZ7 is also classified as a Potentially Hazardous Asteroid. 

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