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A cometary building block was discovered inside LaPaz Icefield (LAP) 02342, a carbonaceous chondrite meteorite found in Antarctica in the 2000s.
An illustration showing how a fragment of cometary building block material was swallowed by an asteroid and preserved inside a meteorite. Image credit: Larry Nittler / NASA.
Meteorites were once part of larger bodies, asteroids, which crashed as a result of collisions in space and survived the journey into the Earth's atmosphere. Their composition can vary considerably from one meteorite to another, reflecting the varied origins of stories in different parent bodies that have formed in different parts of the solar system.
Asteroids and comets have both formed from the disk of gas and dust that once revolved around our young Sun, but they have aggregated at different distances from the Sun, affecting their chemical composition. Compared to asteroids, comets contain larger fractions of water ice and much more carbon.
By studying the chemistry and mineralogy of a meteorite, planetary scientists can reveal details of its formation and indicate the heating and other chemical treatments it has undergone during the solar system's formation years.
A particularly primitive class of meteorites, the carbonaceous chondrites, would have formed beyond Jupiter. One of these meteorites, LAP 02342, is a particularly pristine example with minimal erosion since landing on the surface of the Earth.
In LAP 02342, Carnegie Institution researcher Larry Nittler and his colleagues discovered a tiny slice of carbon-rich primitive material – about a tenth of a millimeter – that has striking similarities to the extraterrestrial dust particles thought to be that they come from comets the outer edges of the solar system.
About 3 to 3.5 million years after the formation of the solar system, but still long before the Earth has finished growing, this fragment was captured by the asteroid growing in the beginning of the meteorite.
By performing a sophisticated chemical and isotopic analysis of the material, the team was able to show that the coated material probably came from the frozen outer solar system, as well as objects from the Kuiper belt, where many comets originate.
"Because this sample of cometary building block material had been swallowed by an asteroid and preserved inside this meteorite, it was protected from the damage caused by the penetration of the Earth's atmosphere," he said. said Dr. Nittler.
"This gave us a glimpse of materials that would not have survived to reach the surface of our planet by themselves, helping us understand the chemistry of the solar system in the beginning."
"Discoveries like this show how important it is to recover valuable meteorites such as LaPaz from Antarctica. We never know what secrets they will reveal, "said Jemma Davidson, a scientist at Arizona State University.
The discovery is reported in a newspaper article Nature Astronomy.
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Larry R. Nittler et al. Cometary building block in a primitive asteroid meteorite. Nature Astronomy, published online April 15, 2019; doi: 10.1038 / s41550-019-0737-8
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