A rare "black diamond" from a prehistoric comet hitting the earth
Rarely charred "black diamond" This 30-gram stone was discovered by the Egyptian geologist Aly Barakat in the Sahara Desert near the Libyan border in December 1996. The 6,000-square-kilometer area is known for its light green glass shards, which were thought to have formed after meteorite impacts millions of years ago. Ancient Egyptians used the Libyan desert glass to make scarab-shaped gemstones, as the funeral jewels of the Egyptian Pharaoh Tutankhamun.
Barakat thinks this dark stone may be a black diamond called black diamond, so he handed the sample to Marco Andreoli of the University of Witwatersrand, South Africa. Years of analysis have shown that this rock may be very rare: it is the first large-scale comet fragment. Until now, scientists have only discovered comet particles in the Earth's atmosphere, and found carbon-rich dust in the ice of Antarctica. The NASA Star Cluster spacecraft also brought back a handful of dust particles from the comet of Wilt II in 2006.
“We are finally able to study the material from the outermost layer of the solar system for the first time,†said Jan Kramers of the University of Johannesburg, member of the Andreoli team. "This is very exciting."
Space diamond
Kramer and his colleagues conducted a series of tests on a one-gram pebble sample to determine its composition. They found that the rock had a very high oxygen-to-carbon ratio - a mysterious blend ratio similar to that found in the Wilt II comet sample and the Antarctic dust debris. They also found that black rock contains diamond blocks, which may be formed by compression of carbon at high pressures of impact.
"People think that comets are dirty snowballs made of ice, which will evaporate under the sun," Kramer said. "But the most resistant part of the comet is carbon. If you compress it, heat it or hit it, you get some kind of glassy carbon, which looks very consistent."
The team then heated the rock fragments to a temperature of 1800 degrees Celsius to release the trapped gas inside. They detected rare gases such as helium, neon, xenon and argon. The argon isotope ratio confirms that the rock was not originally from the Earth. Other isotopic ratios are completely different from those found in known meteorites, all of which come from asteroids, rocky objects formed inside the orbit of Jupiter.
The team believes that comets hit the atmosphere and explode above the desert, similar to what happened in the 1908 Tunguska River in Siberia. The explosion heats and compresses the sand to create the Libyan desert glass. This black stone is part of the solid core of the comet, which absorbs the rare gases of the atmosphere and compresses the carbon into diamonds during the impact.
“On the one hand, the Libyan desert glass is essentially a molten earth surface material. On the other hand, the black pebbles obtained by scientists in the same area are essentially the impact fragments of the comet core. Combining the two, you are not It’s hard to come to a conclusion,†Kramer said.
“There is no doubt that this is a strange object, different from any meteorite we have sampled so far,†said Ingo Leya of the University of Bern, Switzerland, who did not participate in the analysis. But Leia agreed that the rock is likely to come from space, but he is not sure that this is a sample of comets. “The problem is that we have very few comet materials, so we can't compare them as a standard. So it's hard to make a definitive summary or exclude this meteorite from comet.â€
The European Space Agency Rosetta spacecraft will meet with 67P/Churyumov-Glahimenk comet (67P/Churyumov–Gerasimenko) in 2014. It will then deploy a small lander to closely detect the core of the comet, or it may be able to solve the problem. At the same time, Kramer hopes to find more Egyptian rock samples for research.
“This is an area that is very difficult to reach in the Sahara, but there must be more material in the vicinity,†Kramer said. "You want to go there and find more rocks, you have to spend a lot of money, but the cost of comets in outer space is still small."
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