South African researchers have discovered the first evidence of a comet hitting Earth.
"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," said Wits University's David Block on Tuesday.
The researchers found what they believe to be the comet's nucleus – a black pebble, which they have named Hypathia after Ancient Alexandria's female mathematician, astronomer and philosopher.
The research – which will be published in Earth and Planetary Science Letters – was conducted by a team 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, Wits University said.
"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 kilometre 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 university said.
"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" it said.
Kramers said: "It's a typical scientific euphoria when you eliminate all other options and come to the realisation of what it must be."
The impact of the explosion also produced microscopic diamonds, Wits said.
"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.
Comet fragments have only been found as microscopic dust participles in the upper atmosphere and some carbon-rich dust in the Antarctic ice, the university said, adding that space agencies have spent billions of dollars trying to secure the smallest fragment.
"Nasa and the 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.
"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 Block.