Asteroid Apophis less likely to collide with Earth

William Atkins
Thursday, 08 October 2009 18:59

Science - Space

NASA astronomers have revised their estimates as to the likelihood that near-Earth asteroid 99942 Apophis will impact Earth in the year 2036. The chance for a collision has gone from 1-in-45,000 (0.0022%) to 1-in-250,000 (0.0004%). Whew! I feel better!


The asteroid Apophis, also known as 2004 MN4, was discovered in 2004. It caused some eyebrows to upturn in the astronomy community because it looked, initially, like there was a small chance, about a 1-in-40 chance (2.5%), that it would crash into Earth in 2029.

Initial estimates by scientists stated a hit would generate an explosion that would be equivalent to 1,480 megatons of TNT, but that was later downgraded to about 880 megatons of TNT.

As a comparison, the Tunguska event in Siberia (now in the western part of Russia) on June 30, 1908, probably created the equivalent of ten to fifteen megatons of TNT.

New calculations made possible from the 88-inch telescope (directed by the University of Hawaii's Institute for Astronomy), near the summit of Mauna Kea, in Hawaii, have predicted that there is literally no chance of it hitting Earth in 2029.

During this time, however, astronomers decided that because of its close approach to Earth in 2029, there would be another close encounter with Earth in 2036. This was initially set to a 1-in-45,000 chance, or 0.0022%.

And, now in 2009, this percentage was brought it down to 0.0004%, or about a 1-in-250,000 chance of the asteroid hitting Earth.

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