Gathering dust How cathedral rooftops could hold the key to cosmic secrets

Armed only with vacuum cleaners, scientists _| hope that a hunt for extraterrestrial pa ticles willhelp suck up clues about the universe

- Sarah Wild

On the roof of Canterbury Cathedral, in the south-east of England, two planetary scientists are searching for cosmic dust. While the red brick parapet hides the streets far below, only wispy clouds block the deep blue sky that extends into outer space.

The roaring of a vacuum cleaner breaks the silence and researcher Dr Penny Wozniakiewicz, dressed in hazmat suit with a bulky vacuum backpack, carefully traces a gutter with the tube of the suction machine.

"We're looking for tiny microscopic spheres," explained her colleague, Dr Matthias van Ginneken from the University of Kent, also clad in protective gear. "Right now, we are collecting thousands and thousands of dust particles, and we hope there will be a minuscule number that came from space."

Most of the extraterrestrial dust that bombards Earth each year vaporises in the atmosphere - some models suggest that 15,000 tonnes reach Earth's atmosphere. But about 5,200 tonnes of micrometeorites fall to Earth, based on an estimate from Antarctica. These particles, which most likely come from comets and asteroids, are tiny, between 50 microns to two millimetres in diameter.

"You have to be a bit of a detective," said Van Ginneken. The extreme heating on atmospheric entry changes many of the minerals and "you have to figure out the nature of the original particle based on the limited information you have".

Researchers are turning to micrometeorites for clues about the chemistry of asteroids and meteorites. By looking at chemical variants known as isotopes, scientists can understand more about the parent body the cosmic dust came from - and what happened to it as it entered Earth's atmosphere.