Saturday, 28 November 2015

Asteroid 2015 WP2 passes the Earth.

Asteroid 2015 WP2 passed by the Earth at a distance of 229 800 km (0.6 times the average distance between the Earth and the Moon, or 0.16% of the average distance between the Earth and the Sun; but 575.4 times as far from the Earth as the International Space Station and 11.4 times as distant as the satellites that transmit GPS signals), slightly before 1.45 am on Friday 20 November 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2015 WP2 has an estimated equivalent diameter of 2.6-5.7 m (i.e. it is estimated that a spherical object with the same volume would be 2.6-5.7 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 40 km above the ground, with only fragmentary material reaching the Earth's surface.

 
The calculated orbit of 2015 WP2JPL Small Body Database. 

2015 WP2 was discovered on 21 November 2015 (the day after 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 2015 WP2 implies that the asteroid was the 65h object (object P2) discovered in the first second half of November 2015 (period 2015 W).
 
2015 WP2 has a 605 day orbital period and an eccentric orbit tilted at an angle of 1.58° to the plane of the Solar System that takes it from 0.77 AU from the Sun (i.e. 77% of the average distance at which the Earth orbits the Sun, and slightly outside the orbit of Venus) to 2.03 AU from the Sun (i.e. 203% of the average distance at which the Earth orbits the Sun, considerably more than the distance at which 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). 2015 WP2 also has occasional close encounters with the planet Mars, with the next predicted in April 2021.
 
See also...
 
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http://sciencythoughts.blogspot.co.uk/2015/11/asteroid-2015-vd105-passes-earth.htmlAsteroid 2015 VD105 passes the Earth. Asteroid 2015 VD105 passed by the Earth at a distance of 2 777 000 km (7.22 times the average distance between the Earth and the Moon, or 1.86% of the average distance between the Earth and the Sun), slightly before 4.25 pm on Monday 16 November...
http://sciencythoughts.blogspot.co.uk/2015/11/asteroid-2015-vu65-passes-earth.html Asteroid 2015 VU65 passes the Earth.    Asteroid 2015 VU65 passed by the Earth at a distance of 2 009 000 km (5.23 times the average distance between the Earth and the Moon, or 1.34% of the average distance between the Earth and the Sun), slightly before 10.05  pm on Saturday 14...
  

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