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First evidence of space weathering on Comet Wild 2
DR EMILY BALDWIN
ASTRONOMY NOW
Posted: 28 March 2012


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The presence of iron in samples collected from Comet Wild 2 by the Stardust mission and returned to Earth in 2006 have been interpreted as evidence for space weathering, giving the comet its rust-red hue.


A close-up of the nucleus of Comet Wild 2. Image: NASA/JPL.

Less than a milligram of pristine comet grains were scooped up in a silicon-based foam called aerogel, which slowed the particles from speeds of six kilometres per second to a halt over a space of a few millimetres. Since the safe return of the precious material, the particles and the tracks they left in the aerogel have been analysed by scientists all over the world. UK scientist John Bridges from the University of Leicester and colleagues used the Diamond Light Source synchrotron in Oxfordshire and at Leicester University to determine the mineral content of the samples.

“There’s definitely been a lot of high temperature processing going on, which we weren’t really expecting for a comet,” Bridges told attendees of the National Astronomy Meeting yesterday. “The particles are chondritic, rather like what we find in asteroids, compared with the typically “fluffy” material usually associated with comets.”


Aerogel sample of a track (track number 170) showing evidence for space weathering. Image: Bridges/University of Leicester.

Fragments of aluminium-rich chrondules – melt droplets that formed at 1,200 degrees Celsius – are helping to test models of Solar System formation that need to account for the presence of high-temperature, chemically processed material in the comet-forming region.

The scientists also think that bombardment of micrometeoritic debris and solar wind particles – space weathering – over the comet’s 4.5 billion year history is responsible for depositing nanometre-sized grains of iron on the comet and reddening its surface.

“These findings will likely change our views of comets and this could be the real legacy of Stardust,” says Bridges.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
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Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
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3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
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