Month: July 2006

Digging for Shooting Stars in the Antarctic Snow

digging in the snow Jean Duprat/CNRS

You can’t reach the end of a rainbow, but you can find where shooting stars fall on the ground. As a matter of fact, you’ve got some all around you. Thousands of tons of space dust fall on earth every year, and some of it will eventually make it into your home. A small percentage of common household dust — mixed in with the usual mite droppings, diesel engine soot, pollen, dead skin flakes, and other amenities — is stuff of extraterrestrial descent.

But finding these “micrometeorites” in normal dust would mean checking out millions of tiny particles one by one under the electron microscope, and picking out the few that look E.T. to the expert eye. So to improve their chances, scientists figured they had to go look in the most desolate, remote place on earth, hundreds of miles from any living beings and from any sources of human pollution. As I write in this week’s issue of New Scientist, there’s only one place that fits the bill: the Antarctic Plateau, atop a 3 kilometer-thick sheet of ice in the middle of the continent. Even marching penguins never visit.

When a new Franco-Italian base opened a few years ago, micrometeoritologists (assuming that’s a word) figured it was now possible to collect and search large quantities of plateau snow. The new base it made that possible, but not completely easy: the journey still took six months each way.

But the results went beyond the team’s expectations. The air is so clean on the Antarctic Plateau that if you melt and filter the snow, as these guys did, you’ll find hardly any terrestrial dust in it: one of every three dust particles will be from space. (Unless your sieve is too fine: when it comes to really small particles — less than one-fortieth of a millimeter — even Antarctica is not free from pollution).

Many of the particles were probably shed by comets, and may have wandered around the solar system for millions of years before their orbits around the sun happened to cross our planet’s. Some of the particles are relatively large, at half a millimeter — think grains of sand rather than dust — which will make it easier to find the smallest traces of rare elements in them. The fine details of the chemical analysis of comets is something that excites scientists to no end. Comets are thought to be as old as the solar system, and to have changed little since then, so they should be made of the same original ingredients that went into the sun and the planets.