Scientists are elated at the quality, number, and size of cometary dust grains collected by NASA's Stardust mission.
Mission members opened a capsule containing the comet debris on Tuesday in an ultra-clean room at Johnson Space Center in Houston, Texas, US. Earlier that day, the capsule had been flown to Johnson from Utah, where it made a parachute landing on Sunday.
It contains dust collected from the wake of Comet Wild 2, which orbits the Sun between Mars and Jupiter, as well as interstellar dust blown into the solar system from nearby stars. The dust was captured in a tennis-racket shaped collector filled with a sponge-like substance called Aerogel, which is 99.9% empty space and so incredibly light.
When mission members opened the capsule, they found that every aerogel tile had survived the landing intact. They were also able to see hundreds of entry tracks and even some dust particles without the aid of a microscope – something they had not expected to be able to do.
"We were jumping up and down – we were totally overwhelmed by the ability to see this so quickly and so straightforwardly," principal investigator Don Brownlee of the University of Washington in Seattle, US, said at a news briefing on Thursday. "We were the first people in the history of the planet to see comet dust in hand."
Michael Zolensky, a Stardust team member at Johnson, echoed that enthusiasm. He said mission members were anxious about the state of the samples before the capsule was opened.
He said the capsule might not have opened properly, or the dust particles could have smashed the aerogel when they crashed into it at 6 kilometres per second, or the collector might have been "covered by gunk from outgassing of the spacecraft". "We were relieved to find out everything went exactly right," Zolensky said.
Mission scientists will next study the position and shape of the particle tracks and begin to study the particles while they are embedded in the Aerogel and also after they have been removed from it.
They will study the particles' chemical and mineralogical compositions to see the conditions that shaped the comet, which formed about 4.5 billion years ago in an icy ring of rocks beyond Neptune called the Kuiper Belt.
"The Earth has no memory whatsoever of its formation because of all the geological activity" and weathering it has undergone, says Brownlee. But Stardust should shed light on both the early solar system and the history of Earth, says Zolensky. "We think much of the Earth's water and organics – the molecules in our bodies – came from comets," he says. "It's like looking at our great-great-grandparents."
The team will begin distributing comet dust samples to more than 150 scientists around the world next week. They say the samples will provide a basis for understanding observations of Pluto and its moons by NASA's New Horizons mission, due to launch on Thursday, because both objects formed in the Kuiper Belt.
More than 65,000 volunteers have also signed up to search aerogel images for about 100 grains of interstellar dust collected on the "reverse" side of Stardust's Aerogel collector in an Internet project called Stardust@Home.
Stardust was launched in 1999 and flew within 236 kilometres of Comet Wild 2 in January 2004.
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