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Sahara pebble said to come from comet

Oct. 11, 2013
Courtesy of Wits University
and World Science staff

Sci­en­tists have re­ported what they call the first di­rect ev­i­dence of a com­et en­ter­ing the sky and ex­plod­ing, rain­ing down a shock wave of fire that killed eve­ry­thing in its way.

The ev­i­dence is a peb­ble from the com­et, they say. It’s not only the first proof of a com­et strik­ing Earth, mil­lions of years ago, but it could al­so help us one day un­lock the se­crets of the forma­t­ion of our so­lar sys­tem, they add.

An artist’s ren­dition of the com­et ex­plod­ing in Earth’s at­mo­sphere above Egypt (cred­it: Terry Bak­ker)


“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 Da­vid Block of Wits Uni­vers­ity in South Af­ri­ca, one of the re­search­ers.

The com­et en­tered Earth’s at­mos­phere above Egypt about 28 mil­lion years ago, the sci­en­tists ex­plained. En­ter­ing the at­mos­phere, it burst, heat­ing up the sand be­neath it to about 2,000 de­grees Cel­si­us (3,600 Fahren­heit), and form­ing a huge amount of yel­low glass that lies scat­tered over a part of the Sa­hara Des­ert that is larg­er than the state of Del­a­ware. Some of that glass, pol­ished by an­cient jew­elers, is found in King Tu­tan­kha­mun’s brooch, en­cas­ing a strik­ing yel­low-brown scar­ab.

An Egyptian ge­ol­o­gist al­so found a mys­te­ri­ous black peb­ble amid the glass years ago. The au­thors of the new study chem­ic­ally an­a­lyzed the peb­ble and con­clud­ed that it was from the com­et. “It’s a typ­i­cal sci­en­tif­ic eu­pho­ria when you elim­i­nate all oth­er op­tions and come to the real­iz­a­tion,” said Jan Kra­mers of the Uni­vers­ity of Jo­han­nes­burg, a col­la­bo­ra­tor in the re­search.

The im­pact al­so pro­duced mi­cro­scop­ic di­a­monds that are in the peb­ble, he added. “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,” said Kra­mers.

The sci­en­tists named the ob­ject “Hy­pa­tia” af­ter the first well-known fe­male math­e­ma­ti­cian, the as­tron­o­mer-phi­los­o­pher Hy­pa­tia of Al­ex­an­dria.

Com­et frag­ments haven’t been found on Earth ex­cept as mi­cro­scop­ic dust par­t­i­cles in the up­per at­mos­phere and some car­bon-rich dust in the Ant­arc­tic ice, the re­search­ers said. Space agen­cies have spent bil­lions to get pris­tine ma­te­ri­al from a com­et and br­ing it back to Earth. “Now we’ve got a rad­i­cal new ap­proach of stu­dying this ma­te­ri­al, with­out spend­ing bil­lions of dol­lars,” said 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,” added Block.

Kramers said in an e­mail that the sci­en­tists es­ti­mat­ed the im­pacting ob­ject “should have been at least 20 tonnes or so to pro­duce the shock di­a­monds, probably much more. But that would be only the im­pacted part. The orig­i­nal com­et would have been bro­ken up on hit­ting the at­mos­phere, with most of [it] be­ing oblit­er­ated in ex­plo­sions.”


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Scientists have reported what they call the first direct evidence of a comet entering the sky and exploding, raining down a shock wave of fire that obliterated every life form in its path. The evidence is a pebble from the actual comet, they say. It’s not only the first proof of a comet striking Earth, millions of years ago, but it could also help us one day unlock the secrets of the formation of our solar system, they add. “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 David Block of Wits University in South Africa, one of the researchers. The comet entered Earth’s atmosphere above Egypt about 28 million years ago, the scientists explained. Entering the atmosphere, it burst, heating up the sand beneath it to about 2,000 degrees Celsius (3,600 Fahrenheit), and forming a huge amount of yellow glass that lies scattered over a part of the Sahara Desert that is larger than the state of Delaware. Some of that glass, polished by ancient jewellers, is found in King Tutankhamun’s brooch, encasing a striking yellow-brown scarab. An Egyptian geologist also found a mysterious black pebble amid the glass years ago. The authors of the new study chemically analyzed the pebble and concluded that it was from the comet. “It’s a typical scientific euphoria when you eliminate all other options and come to the realization,” said Jan Kramers of the University of Johannesburg, a collaborator in the research. The impact also produced microscopic diamonds that are in the pebble, he added. “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,” said Kramers. The scientists named the object “Hypatia” after the first well-known female mathematician, the astronomer and philosopher Hypatia of Alexandria. Comet fragments haven’t been found on Earth except as microscopic dust particles in the upper atmosphere and some carbon-rich dust in the Antarctic ice, the researchers said. Space agencies have spent billions to get pristine material from a comet and bring it back to Earth. “Now we’ve got a radical new approach of studying this material, without spending billions of dollars,” said 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,” added Block. Kramers said in an email that the scientists estimated the impacting object “should have been at least 20 tonnes or so to produce the shock diamonds, probably much more. But that would be only the impacted part. The original comet would have been broken up on hitting the atmosphere, with most of [it] being obliterated in explosions.”