June 30, 2009

Study: Tunguska explosion caused by comet

U.S. scientists say research involving the exhaust plume from a NASA space shuttle launch suggests the 1908 Tunguska explosion was caused by a comet

The mysterious explosion leveled 830 square miles of Siberian forest and a cause has never been determined. But Cornell University researchers say findings from their study indicated the explosion was nearly certainly caused by a comet entering the Earth's atmosphere.

It's almost like putting together a 100-year-old murder mystery, said Professor Michael Kelley, who led the study. The evidence is pretty strong that the Earth was hit by a comet in 1908.

The researchers contend the massive amount of water vapor spewed into the atmosphere by the comet's icy nucleus was caught by high-energy eddies in a process called two-dimensional turbulence, which explains why noctilucent clouds formed a day later many thousands of miles away.

Noctilucent clouds are the Earth's highest clouds, forming naturally in the mesosphere at about 55 miles over the polar regions during the summer months. The space shuttle exhaust plume, the researchers say, resembled the comet's action.

Kelley and his colleagues saw the noctilucent cloud phenomenon days after space shuttle Endeavour was launched Aug. 8, 2007. Similar cloud formations had been observed following launches in 1997 and 2003.

The study appears in the June 24 issue of the journal Geophysical Research Letters.