Asteroid 99942 Apophis will fly by the Earth at a distance of 14.5 million km on Wednesday 9 January 2012, slightly under 40 times the distance to the Moon. The asteroid is roughly 270 m in diameter and has an estimated mass of 27 megatonnes; enough to cause considerable damage should it hit the Earth. This is not a likely event this year, but when the object was discovered in December 2004 it was estimated that there was a 2.7% chance that it would hit the Earth in 2029, and there is still considered to be a one in 250 000 chance it could strike the Earth in 2036. As such 99942 Apophis will be carefully studied on this, and subsequent, passes, with the aim of better refining this estimate.
The orbit of 99942 Apophis. Image created using the JPL Small Body Database Browser.
99942 Apophis, which is named after a malign Egyptian serpent-god, circles the Sun every 323.5 days, in an orbit that takes it in to 0.746 AU from the Sun (74.6% of the distance at which the Earth orbits the Sun, just outside the orbit of Venus) and out to 1.1 AU from the Sun (1.1 times as far from the Sun as the Earth). It belongs to a family of Near-Earth Asteroids called the Atens, which have eccentric orbits and spend most of their time inside the Earth's orbit but which still cross it to reach the outermost point of their orbit.
See also The Earth approaches its perihelion, Possible second meteor shower to coincide with the Geminids, Asteroid 4179 Toutatis/1989 AC to fly past the Earth, The Geminid Meteors and The Leonid Meteors.
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