Friday 5 May 2017

Asteroid 2017 JA passes the Earth.

Asteroid 2017 JA passed by the Earth at a distance of  99 660 km (0.26 times the average distance between the Earth and the Moon, 0.007% of the average distance between the Earth and the Sun, or a little less than three times the distance at which satellites in geostationary orbits circle the Earth), slightly before 7.25 am GMT on Tuesday 2 May 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 JA has an estimated equivalent diameter of 2-9 m (i.e. it is estimated that a spherical object with the same volume would be 2-9 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 more than 32 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 JA. Minor Planet Center.

2017 JA was discovered on 1 May 2017 (the day before its closest approach to the Earth) 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 2017 JA implies that the asteroid was the first object (object A) discovered in the first half of May 2017 (period 2017 J). 

2017 JA has a 1044 day orbital period and an eccentric orbit tilted at an angle of 1.13° to the plane of the Solar System, which takes it from 0.78 AU from the Sun (i.e. 78% of he average distance at which the Earth orbits the Sun, outside the orbit of the planet Venus) to 3.25 AU from the Sun (i.e. 325% of the average distance at which the Earth orbits the Sun, considerably over twice the distance at which the planet Mars orbits the Sun). 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 common, with the last having occurred in September 2014 and the next predicted in October 2069. 

2017 JA also has frequent close encounters with the planets Venus, which it is next predicted to pass in January 2058, and Mars which it is next predicted to pass in January 2064. 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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