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Pristine space rocks older than the Sun

Precious cargo A meteorite which crashed to Earth earlier this year contains grains older than the solar system itself, according to scientists.

These rare and primitive space rocks, called carbonaceous chondrites, act as time capsules, providing astronomers with a window into the formation of the Sun and planets, four and a half billion years ago.

Carbonaceous chondrites also contain organic carbon molecules, materials that may be the precursors to life on Earth.

The meteorite was spotted as a fast moving fireball in the skies over California and Nevada on the morning of 22 April 2012, and tracked by US Air Force and doppler weather radar installations.

This allowed scientists to quickly recover several fragments in the Sutter's Mill area, before they were contaminated by rain, which would alter their composition.

Sutter's Mill became world famous in 1848 as the location that sparked the California gold rush.

An analysis carried out by researchers including Dr Peter Jenniskens from the SETI Institute and NASA's Ames Research Center, confirmed the unusually pristine condition of three fragments.

According to Jenniskens, the three and a half metre wide meteor, airburst with the force of a four kilotonne impact over the Sierra Nevada foothills.

"The meteorites survived a record breaking atmospheric entry speed of 28.6 kilometers per second from an orbit close to that of Jupiter-family comets," says Jenniskens.

Ancient artefacts

Writing in the journal Science, Jenniskens says the Sutter's Mill meteorite samples contain a significant abundance of pre-solar grains.

These are minerals older than the solar system, and are considered to be representative of the solar nebula out of which the solar system condensed.

Jenniskens says it was important for to recover fragments of the meteorite before they were exposed to rain

"Carbonaceous chondrites are almost 30 per cent empty, so they act like sponges and suck in water, which rapidly causes chemical reactions changing their composition," says Jenniskens.

According to Jenniskens, it was the first time they had a chance to study this type of meteorite before it came into contact with water on Earth.

The significance of this was evident in a comparison of two samples. One fragment was recovered after exposure to rain and showed significant changes in the composition of sulfur-bearing minerals.

"The considerable mineralogy, diversity and geochemical features in the pristine samples, indicate they are regolith breccia, part of the surface of the asteroid that spawned them," says Jenniskens.

"This provides us with clues to the complex formation history of the parent asteroid."

"We found oldamite, which is a calcium sulfide, so sensitive to water, if you breathe on a sample, it disappears," says Jenniskens.

"These are normally found in evolved meteorites that come from the area where the Earth and Venus formed, while carbonaceous chondrites come from very primitive asteroids that form further out."

"So this tells us about collisions between primitive and evolved asteroids at the time this meteorite formed."