Stardust particles made of 'fire and ice'

The particles the Stardust probe brought back to Earth in January are a mixture of extremely hot and cold minerals pointing to a mixed origin of the Wild 2 comet, Nasa scientists said.

“Remarkably enough, we have found fire and ice,” said Donald Brownlee, Stardust chief investigator said in a statement on the Nasa website that summed up a press conference held on Monday at the Johnson Space Centre (JSC) in Houston, Texas.

Rather than the balls of ice, dust and gas astrophysicists thought they were, comets turn out to be celestial bodies of complex and varied origins, said the University of Washington professor.

“It seems that comets are a mixture of materials formed at all temperatures, at places very near the early sun and at places very remote from it,” said Michael Zolensky, Stardust curator and co-investigator at JSC.

The Wild 2 particles include olivine, a rock found in abundance in the green sand on some Hawaiian beaches. Its presence in the comet’s dust trail was a surprise, scientists said. Olivine’s components include iron, magnesium and other elements.

The Wild 2 samples have other high-temperature materials containing calcium, aluminum and titanium.

A Stardust capsule carrying a teaspoonful of space dust parachuted to Earth in the Utah desert on January 15 after a nearly seven-year journey across 4,63-billion kilometres.

The dust was captured in super-light “aerogel”, a sturdy, sponge-like solid carried on the spacecraft.
Some of the interstellar particles were collected as the craft passed through the aura of the comet Wild Two. The rest were harvested along the course of the Stardust craft’s journey.

The interstellar dust is being analysed by about 150 scientists around the world, Brownlee said, adding that the laboratories were provided the samples for free.

Millions of comets encircle the sun and as they near the star, the solar heat melts the ice, leaving a trail of dust that is illuminated as a long tail.

Linked in superstitious minds with great events, good and bad, comets are equally beguiling for astrophysicists, who believe they are the most primitive material from the early days of the solar system.

They are considered to be the leftovers from the massive cloud of gas and dust that condensed and then coagulated to form the sun, the planets and other parts of the solar system about 4,6-billion years ago.

Scientists say understanding the substance and structure of comets provides clues of how Earth came into being. - AFP