Asteroid 2017 YE5 passed by the Earth at a distance of about 5 963 000 km (15.5 times the average distance between the Earth and the Moon, or 3.99% of the distance between the Earth and the Sun), slightly after 8.50 pm GMT on Thursday 21 June 2018. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2017 YE5 has an estimated equivalent diameter of 250-780 m (i.e. it is estimated that a spherical object with the same volume would be 250-780 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 35 000 to 1 175 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 3-11 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 YE5. Minor Planet Center.
2017 YE5 was discovered on 21 December 2017 by the Oukaimeden Observatory, in Marrakech. The designation 2017 YE5 implies that it was the 130th asteroid (asteroid E5) discovered in the second half of December 2017 (period 2017 Y).
2017 TE5 has an 1730 day orbital period and an eccentric orbit tilted at an angle of 6.21° to the plane of the Solar System, which takes it from 0.82 AU from the Sun (i.e. 82% of he average distance at which the Earth orbits the Sun) to 4.82 AU from the Sun (i.e. 482% of the average distance at which the Earth orbits the Sun, and 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 February 1994 and the next predicted in February 2051. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2017 TE5 is also classified as a Potentially Hazardous Asteroid.
2017 ME5 also has frequent close encounters with the planets Venus, which it is thought to have last passed in June 1908, Mars, which it last came close to in November 1964 and is next predicted to pass in July this year, and Jupiter, which it last approached in June 2012, and is next predicted to do so in October 2035. 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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