Big Meteorite Creates Big Mysteries

Scientists havediscovered a beach ball-sized meteorite a half-mile below a giant crater inSouth Africa.

The145-million-year-old meteorite, found in the Morokwengcrater, has a chemical composition unlike any known meteorite.

It is also anunusual find because it was largely unaltered by the extreme heat from theimpact.

The study isdetailed in the May 11 issue of the journal Nature.

Oddball meteorite

Scientists havecollected thousands of various meteorites over the years and tell them allapart by their various structural, chemical, and mineralogical compositions.The specific concentrations of platinum group elements in the newfound 10-inch(25 centimeter) meteorite place it in the "LL-ordinary chondrite"group of meteorites.

But othercharacteristics set it apart from the group, such as having silicate andsulfide minerals rich in iron, but no metallic iron-nickel phase.

"So it is 'anotherkind' of LL-ordinary chondrite that we do not have inour collections," said study co-author Alexander Shukolyukovof the Scripps Institution of Oceanography and the University of California,San Diego.

A potentialimplication of this odd meteorite, he said, is that the bombardment ofmeteorites 145 million years ago was different than those crashing into Earthmore recently.

The researcherscan't say for sure why this fragment is preserved. Current models indicate thatno unaltered fragments can survive large impacts, which, Shukolyukovsuggests, implies the models are incomplete.

Just a remnant

It is also clearthat it was much, much larger than 10 inches in diameter when it smacked thesurface.

An820-foot-diameter (250 meters) meteorite would slam into the planet and releaseenergy on the order of about 1,000 megatons--about 66,000 times the strength ofthe 15-kiloton bomb dropped on Hiroshima. The impact would create a crater 3miles (5 kilometers) across, Shukolyukov told SPACE.com.

In contrast, the Morokweng crater is a whopping 43 miles across (70kilometers), so the meteorite that created it must have been substantiallybigger than 820 feet.

The raw energyproduced by the impact also generates a lot of heat--3,100 to 24,700 degreesFahrenheit (1700 to 13,700 Celsius)--so it's surprising that anything remains ofthe rock at all, and even more so that it is unaltered. Generally the heatcompletely melts or vaporizes meteorites, and if anything is left, it doesn'tresemble its original state.

"It may be thatthis fragment was just a separate small meteorite that accompanied a 'bigguy," Shukolyukov said.

However, accordingto the models, a trailing object would have completely melted.

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