Researchers find unique meteorites

In Sweden discovered "fossil" meteorite is similar to no known meteorite type

The newly discovered meteorite (dark gray), embedded in 470 million year old limestone. © Birger Schmitz
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Unique find: In a Swedish quarry, researchers have discovered a completely new type of meteorite. Its composition distinguishes the 470-million-year-old meteorite from all previously known, as researchers report in the journal "Nature Communications". They suspect that the find could be the fragment of a momentous collision in the asteroid belt.

There are plenty of meteorites on earth - and new ones are constantly falling down. 86 percent of them belong to the chondrites, rocks with spherical silicate inclusions. A few decades ago, however, researchers noticed something strange in a low-iron subgroup of chondrites: a strikingly large number of these L-chondrites are around 500 million years old - far younger than most other types of meteorites that came from the early days of the solar system.

Who was the collision partner?

"These meteorites seem to have gone through a massive collision event at that time, " explain Birger Schmitz of the University of Lund in Sweden and his colleagues. This collision in the asteroid belt probably broke a larger celestial body. His fragments were flung out of his belt and hit Earth.

"In marine limestone strata, which formed around 470 million years ago, there is evidence of a 100-fold increase in L-chondrites and micrometeorites, " the researchers report. So far, however, it has remained puzzling with which asteroid the mother lump of these meteorites could have collided.

The unique chunk was discovered in this quarry in southern Sweden. © Birger Schmitz

Conspicuous match

The very first relic of this unknown collision partner could now have Schmitz and his colleagues identified. It is an eight-centimeter-long and 6.5-centimeter-wide rock, the researchers found in the limestone of the Thorsberg quarry in Sweden. Dating of the layer revealed that the meteorite must have collapsed into the sea some 470 million years ago and then was embedded in the seabed. display

The sterplana 65 baptized meteorite struck with it almost at the same time as the numerous known L-chondrites, as the scientists explain. Isotope analysis confirms this: The chunk was created up to one million years at the time of the presumed collision in space. However, sterplana 65 can not come from the "mother lump" of the L-chondrites, as revealed by further analyzes of the chromium and oxygen isotopes.

Unique and unknown

Instead, the newly discovered meteorite represents something hitherto completely unknown: "plsterplana 65 has no documented correspondence among the known meteorites that fell to Earth at that time, " say Schmitz and his colleagues. And in all other known types of meteorites, the new find does not fit into it.

"Mineralogical and petrological data support the conclusion that plsterplana 65 represents a hitherto completely unknown type of meteorite, " the researchers note. The rock is unique and stands out from all known "heavenly messenger" from.

Is the sterplana 65 meteorite the only relic of the momentous collision in the asteroid belt 470 million years ago? NASA / JPL

An "extinct" meteorite?

According to the researchers, this can be concluded in two ways: First, it could still be a lot of big, about 500 million years ago - and thus relatively late in the history of the solar system The variety of meteorites and precursor objects in the asteroid belt has been greater than today. Some of these chunks were apparently destroyed so severely in collisions that today there are hardly any fragments of them left that could hit the earth as meteorites.

"This could be the first documented case of an 'extinct' meteorite, " explain the scientists. "This type of meteorite does not fill the earth today, because its original celestial body was completely destroyed by collisions."

Witness the momentous collision?

Even more exciting, however, is the second conclusion that the researchers draw from the features of sterplana 65: The meteorite could be a litter of the mysterious asteroid, some 470 million years ago collided with the "mother body" of the L-chondrites. Both the timing of its formation and the shock marks in the rock enclosures of sterplana 65 speak for it, as the scientists report.

"It is possible that the collision between the L-chondrite precursor and the Osterplana 65 precursor almost completely destroyed the latter, " said Schmitz and his colleagues. "While the L-Chondrites precursor crumbled into innumerable smaller objects that have since fallen as meteorites, there was not enough left of his collision partner." Österplana 65 could thus be one of the last relics of this asteroid. (Nature Communications, 2016; doi: 10.1038 / ncomms11851)

(Nature, 15.06.2016 - NPO)