Oct 8, 2013 by Sci-News.com


A mysterious black pebble found by an Egyptian geologist at the Libyan Desert Glass strewnfield provides the first ever evidence of a comet entering Earth’s atmosphere and exploding.

The comet entered the atmosphere above Egypt about 28.5 million years ago. It exploded, heating up the sand beneath it to a temperature of about 2,000 degrees Celsius, and resulting in the formation of a huge amount of yellow silica glass, called the Libyan Desert Glass.
A magnificent specimen of the Libyan Desert Glass, polished by ancient jewelers, is found in Tutankhamun’s brooch with its striking yellow-brown scarab.
Prof Jan Kramers from the University of Johannesburg, a lead author of the paper published online in the journal Earth and Planetary Science Letters, and his co-authors analyzed the diamond-bearing pebble ‘Hypatia,’ named in honor of the first well known female mathematician, astronomer and philosopher, Hypatia of Alexandria.
After conducting highly sophisticated chemical analyses on this pebble, the team came to the inescapable conclusion that it represented the very first known specimen of a comet nucleus, rather than simply an unusual type of meteorite.
“It’s a typical scientific euphoria when you eliminate all other options and come to the realization of what it must be,” Prof Kramers said.
“The impact of the explosion also produced microscopic diamonds. Diamonds are produced from carbon bearing material. Normally they form deep in the earth, where the pressure is high, but you can also generate very high pressure with shock. Part of the comet impacted and the shock of the impact produced the diamonds.”

Comet material is very elusive. Comet fragments have not been found on Earth before except as microscopic sized dust particles in the upper atmosphere and some carbon-rich dust in the Antarctic ice. Space agencies have spent billions to secure the smallest amounts of pristine comet matter.
“NASA and ESA spend billions of dollars collecting a few micrograms of comet material and bringing it back to Earth, and now we’ve got a radical new approach of studying this material, without spending billions of dollars collecting it,” Prof Kramers said.
“Comets contain the very secrets to unlocking the formation of our Solar System and this discovery gives us an unprecedented opportunity to study comet material first hand,” said co-author Prof David Block of Wits University.
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Bibliographic information: Jan D. Kramers et al. 2013. Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass strewnfield, SW Egypt: Evidence for a shocked comet fragment. Earth and Planetary Science Letters, vol. 382, pp. 21–31; doi: 10.1016/j.epsl.2013.09.003