Comets haven't been observed entering Earth's atmosphere (shown here: Hale-Bopp in 1997).
A team scientists in South Africa said on Thursday (October 10) they have discovered the first evidence of a comet entering Earth's atmosphere.
Professor David Block, part of the team of scientists, unveiled the findings of the first documented case of a comet ever striking Earth at Wits University in Johannesburg.
A black diamond-bearing pebble found years earlier by an Egyptian geologist is at the heart of the research, with scientists saying this represents the very first known hand specimen of a comet nucleus - and not a meteor as originally thought.
"We discovered that this was not a meteor, in other words a chunk of rock which entered the Earth's atmosphere and burnt up, but this was actually a comet from the very depths of outer space and of outer time which had entered the Earth's atmosphere and exploded. This, allow me to state, is the first documented case of a comet ever striking our planet Earth," said Block.
Scientists calculate the comet entered the Earth's atmosphere above Egypt some 28 million years ago. As it entered the atmosphere, it exploded, heating up the sand and resulting in a vast amount of silica glass which lies scattered over some 6,000 km area in the Sahara. The black pebble, named 'Hypatia' after an ancient female astronomer, mathematician and philosopher from Alexandria, was found among these shards of silica.
One example of the silica glass was polished by ancient jewellers and placed in Tutankhamun's brooch in the shape of a yellow scarab.
Block said he and his colleagues, 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, were elated by the rare discovery.
"They are exceedingly rare events and that's why we are so excited to hold a piece of a comet in our hands. Because comets normally never enter our neighbourhood. Yes, we can see them in the sky with glowing tails and fiery heads but they never enter our Earth's atmosphere except for this one," he said.
Block explained that comet material was very rare and fragments had not been found before except as microscopic dust particles in the upper atmosphere and in Antarctic ice. Space agencies have spent billions to secure the smallest amounts of pristine comet matter, but scientists say this could represent a radical and cheaper way of studying the material.
He added that the team believe the fragment could unlock some of the secrets to understanding the universe.
"So we've literally got here at our very fingertips the unique methodologies now to understand the very birthing of our sun, our closest star, and the surrounding planets," he said.
The research is due to be published in 'Earth and Planetary Science Letters' in November.
The last comet to dazzle Earth's night-time skies was Comet Hale-Bopp which visited in 1997.
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