* Astronomy

Researchers from Cornell University have confirmed that the mysterious Tunguska explosion was caused by a comet. In 1908, this explosion levelled 830 square miles of the Siberian forest. Now the new findings have been validated, strangely enough by the exhaust plume from a NASA space shuttle. The two events are related by bright and night-visible clouds, also known as "noctilucent" clouds which are developed when ice particles form at high altitudes in extremely cold temperatures.

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Space shuttle exhaust hints comet caused Tunguska blast
Was the Tunguska explosion of 1908 caused by a comet hitting Earth? That's the claim of a new study based on the behaviour of water vapour from the space shuttle's exhaust. But other scientists dispute the claim, and say the evidence still points to a stony meteoroid as the culprit.
The explosion was somewhere in the megaton range, and destroyed a great swathe of forest in eastern Siberia. The most likely cause is the impact of an object from space, exploding as an air-burst several kilometres up. What type of object is unclear, however, because no large solid remnants have been found.

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1908 Tunguska Explosion Was Caused by a Comet
The mysterious 1908 Tunguska explosion that levelled 830 square miles of Siberian forest was almost certainly caused by a comet entering the Earth's atmosphere, says new Cornell University research. The conclusion is supported by an unlikely source: the exhaust plume from the NASA space shuttle launched a century later.
The research, accepted for publication (June 24, 2009) by the journal Geophysical Research Letters, published by the American Geophysical Union, connects the two events by what followed each about a day later: brilliant, night-visible clouds, or noctilucent clouds, that are made up of ice particles and only form at very high altitudes and in extremely cold temperatures.

"It's almost like putting together a 100-year-old murder mystery. The evidence is pretty strong that the Earth was hit by a comet in 1908" - Michael Kelley, the James A. Friend Family Distinguished Professor of Engineering at Cornell who led the research team.

Previous speculation had ranged from comets to meteors.
The researchers contend that the massive amount of water vapour spewed into the atmosphere by the comet's icy nucleus was caught up in swirling eddies with tremendous energy by a process called two-dimensional turbulence, which explains why the noctilucent clouds formed a day later many thousands of miles away.
The space shuttle exhaust plume, the researchers say, resembled the comet's action. A single space shuttle flight injects 300 metric tons of water vapour into the Earth's thermosphere, and the water particles have been found to travel to the Arctic and Antarctic regions, where they form the clouds after settling into the mesosphere.
Kelley and collaborators saw the noctilucent cloud phenomenon days after the space shuttle Endeavour (STS-118) launched on Aug. 8, 2007. Similar cloud formations had been observed following launches in 1997 and 2003.
Following the 1908 explosion, known as the Tunguska Event, the night skies shone brightly for several days across Europe, particularly Great Britain -- more than 3,000 miles away. Kelley said he became intrigued by the historical eyewitness accounts of the aftermath, and concluded that the bright skies must have been the result of noctilucent clouds. The comet would have started to break up at about the same altitude as the release of the exhaust plume from the space shuttle following launch. In both cases, water vapour was injected into the atmosphere.

The scientists have attempted to answer how this water vapour travelled so far without scattering and diffusing, as conventional physics would predict.

Source: Cornell University

-- Edited by Blobrana on Thursday 25th of June 2009 01:52:52 PM