Asteroid (418849) 2008 WM64 passed by the Earth at a distance of about 11 754 000
km (30.6 times the average distance between the Earth and the Moon, or
7.86% of the distance between the Earth and the Sun), slightly before 4.35 pm
GMT on Tuesday 24 December 2019. There was no danger of
the asteroid hitting us, though were it to do so it would have
presented a considerable threat. (418849) 2008 WM64 has an estimated
equivalent
diameter of 140-450 m (i.e. it is estimated that a spherical object with
the same volume would be 140-450 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 300-176 000 times as powerful as the Hiroshima
bomb. Such an impact would result in an impact crater 2-7 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 (418849) 2008 WM64. Minor Planet Center.
(418849) 2008 WM64 was discovered on 24 November 2008 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 2008 WM64
implies that the asteroid was the 1548th object (object M64 -
in numbering asteroids the letters A-Y, excluding I, are assigned
numbers from 1 to 24, with a number added to the end each time the
alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc., which means that M64 = 12 + (24 X 64) = 1548) discovered in the second half of November 2008 (period 2008 ),
while the longer designation, 418849, indicates that it was the 418 849th asteroid discovered
overall (asteroids are not given this longer designation immediately, to
ensure that numbered objects are genuine asteroids that have not been
previously described).
(418849) 2008 WM64 is calculated to have a 368 day orbital
period and an elliptical orbit tilted at an angle of 33.5° to the plain of the
Solar System that takes it from 0.90 AU from the Sun (i.e. 90% of the average
distance at which the Earth orbits the Sun) to 1.11 AU from the Sun (i.e. 111%
of the average distance at which the Earth 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 extremely common, with the last having occurred
in July this year (2019) and the next predicted in December next year (2020). As
an asteroid probably larger than 150 m in diameter that occasionally
comes within 0.05 AU of the Earth, (418849) 2008 WM64 is also classified
as a Potentially Hazardous Asteroid.
See also...
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