Home > General Astronomy > Close Encounters with Asteroid 2005 YU55

Close Encounters with Asteroid 2005 YU55

This evening (8 November 2011) at 2328 GMT a 400m diameter asteroid will hurtle past the Earth, missing us by an astronomical whisker, less than 200,000 miles. The chunk of space debris in question is snappily titled 2005 YU55.

Radar image of 2005 YU55 taken at 1945UT on 7 November 2011, when the asteroid was 1.38 million km away

This kind of asteroid fly-by is rather rare. The last time that something this size passed so close to us was in 1976, and the next time it’s due to happen (that we know of) is 2028. Still, tonight’s pass poses absolutely no risk to the Earth.

Asteroid 2005 YU55 was discovered, as its name suggests, is 2005. This designation method is used by the Minor Planet Center, and designates minor planets until a proper name is given (if ever). Upon discovery it became clear that this asteroid was one of the Apollo asteroids, near-Earth asteroids named after 1862 Apollo, the first of the group to be discovered. The Apollo asteroids are all Earth-crossing asteroids, and so warrant special attention. The fact that their orbits cross that of the Earth does not automatically mean they pose a threat of impact, but does mean that we need to very carefully monitor their orbits in case they are on a collision course with us in the future.

Astronomers rank near-Earth asteroids relative to the risk they pose to us using the Torino Impact Hazard Scale. This ten point scale runs from 0, meaning that “the likelihood of a collision is zero, or is so low as to be effectively zero”, to 10, meaning “a collision is certain, capable of causing global climatic catastrophe that may threaten the future of civilization as we know it”. 2005 YU55 is currently ranked at 0 in this scale. There are no asteroids currently known that are ranked higher than 1. The highest ranking ever given was 4, given briefly to asteroid Apophis, meaning “a close encounter, meriting attention by astronomers…[with] a 1% or greater chance of collision capable of regional devastation”, but this has since been downgraded to a 0 based on new observations refining its orbit.

Torino Scale

Asteroid 2005 YU55 will not be visible to the naked eye, but amateur astronomers with good telescopes, and knowledge of how to use them, might locate it. See Robin Scagell’s excellent description of how to find it over at the Society for Popular Astronomy.

If 2005 YU55 did hit the Earth (it won’t) it could certainly destroy a large city and cause significant loss of life (to find out what would happen head over to the Down 2 Earth Impact Simulator) which is just one of the reasons that asteroid observation projects are so important.

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