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  Solar wind gives asteroids a tanning
Asteroids become redder the longer they stay out in the sun, a finding that could help determine our planetary origins, say US and European researchers.

The research, which appears in the latest edition of Nature, shows that the fresh surface of asteroid fragments redden in less than a million years, much faster than previously thought.

"Asteroids seem to get a sun tan very quickly," says research lead author Dr Pierre Vernazza from the European Southern Observatory (ESO). "The charged, fast moving particles in the solar wind damage the asteroid's surface at an amazing rate."

It has long been known that asteroid surfaces change appearance over time, but the actual processes behind this weathering and the time involved were controversial.

Using the ESO's New Technology Telescope and the Very Large Telescope in Chile, as well as telescopes in Spain and Hawaii, they analysed the surfaces of S-type, stony asteroids, and Q-type asteroids, rich in the minerals pyroxene and olivine. These asteroid were formed by collisions as recently as one million years ago.

By comparing the age of the asteroids and their colour, they determined solar wind was the culprit.

Solar wind, which consists of highly energetic particles released by the sun, is different to ultraviolet radiation, which is responsible for tanning human skin.
Meteoric connections

The finding is significant, as it will allow astronomers to better determine the origin of meteorites - asteroid fragments that fall to earth.

"Meteorites are time capsules from the beginning of the solar system," says Vernazza.

"The value of their record of the earliest epoch of planetary formation is, with a few exceptions, compromised by the lack of precision with which we can pinpoint the location of their parent bodies."

"Our results will help us to make the link between meteorites and asteroids. They will help us to determine the source location of meteorites."

Associate Professor Charley Lineweaver of the Planetary Science Institute at the Australian National University in Canberra says the study's findings are significant.

Lineweaver says, understanding where meteorites originate from helps to pinpoint where the earth collected its material during its formation.

But until now space weathering has made it hard to draw a link between meteorites and asteroids, he says.

"[Space] weathering is like taking an archaeological site and throwing dust over it."

"We don't have much data on how far away a particular meteorite comes from," says Lineweaver.

"Asteroids possess a wealth of information [on the early solar system] and we would love to connect this to the few meteorites we have."
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