[meteorite-list] First Ever Evidence Of A Comet Striking Earth

[Ron Baalke]

http://www.uj.ac.za/EN/Newsroom/News/Pages/First-ever-evidence-of-a-comet-striking-earth.aspx

First ever evidence of a comet striking earth 
University of Johannesburg
October 8, 2013

The first ever evidence of a comet entering Earth's atmosphere and exploding, 
raining down a shock wave of fire which obliterated every life form in 
its path, has been discovered by a team of South African scientists and 
international collaborators, and will be presented at a public lecture 
on Thursday.

The discovery has not only provided the first definitive proof of a comet 
striking Earth, millions of years ago, but it could also help us to unlock, 
in the future, the secrets of the formation of our solar system.
 
"Comets always visit our skies - they're these dirty snowballs of ice 
mixed with dust - but never before in history has material from a comet 
ever been found on Earth," says Professor David Block of Wits University.
 
The comet entered Earth's atmosphere above Egypt about 28 million years 
ago. As it entered the atmosphere, 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 which lies scattered 
over a 6 000 square kilometer area in the Sahara. A magnificent specimen 
of the glass, polished by ancient jewellers, is found in Tutankhamun's 
brooch with its striking yellow-brown scarab.

The research, which will be published in Earth and Planetary Science Letters, 
was conducted by a collaboration of geoscientists, physicists  and astronomers 
including Block, lead author Professor Jan Kramers of the University of 
Johannesburg, Dr Marco Andreoli of the South African Nuclear Energy Corporation, 
and Chris Harris of the University of Cape Town. 
 
At the centre of the attention of this team was a mysterious black pebble 
found years earlier by an Egyptian geologist in the area of the silica 
glass. After conducting highly sophisticated chemical analyses on this 
pebble, the authors came to the inescapable conclusion that it represented 
the very first known hand specimen of a comet nucleus, rather than simply 
an unusual type of meteorite.
 
Kramers describes this as a moment of career defining elation. "It's a 
typical scientific euphoria when you eliminate all other options and come 
to the realisation of what it must be," he 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," says Kramers.
 
The team have named the diamond-bearing pebble "Hypatia" in honour of 
the first well known female mathematician, astronomer and philosopher, 
Hypatia of Alexandria.
 
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 (European Space Agency) 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," says Kramers.
 
The study of Hypatia has grown into an international collaborative research 
programme, coordinated by Andreoli, which involves a growing number of 
scientists drawn from a variety of disciplines. Dr Mario di Martino of 
Turin's Astrophysical Observatory has led several expeditions to the desert 
glass area.
 
"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," says Block.
 
Public lecture:
 
Please join Professor Jan Kramers, Professor David Block and Dr Marco 
Andreoli as they reveal their new discovery. 
 
Date: Thursday, 10 October 2013
Time: 17:30 for 18:00
Venue: Auditorium 3, Wits Science Stadium, West Campus
RSVP: 011 717 1146 or kelebogile.tadi at wits.ac.za
 
Images:
High resolution images can be downloaded by left clicking on the images 
available at:
http://www.wits.ac.za/newsroom/newsitems/201310/21649/news_item_21649.html
 
Online paper:
An online version of the scientific journal article can be accessed at:
http://www.sciencedirect.com/science/article/pii/S0012821X13004998