Stardust Brought Back Comet Pieces 10 Years Ago

On a January morning 10 years ago, tiny pieces of a comet landed on Earth inside of a spacecraft. NASA's Stardust return-sample capsule arrived in Utah with its precious cargo on board, and ever since, principal investigator Don Brownlee (University of Washington) has been combing through the samples to see what it collected after seven years in space.

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Even years later, surprises have emerged. In 2014, Brownlee's team announced that probable interstellar particle tracks were found in the aerogel and aluminum foil particle detectors. A newer paper (by another team) submitted to the Lunar and Planetary Science Conference in Houston suggests this interplanetary dust is also made up in part of glass, which is a rare element in meteoroids.

"We're constantly learning new things using better and better techniques," Brownlee told Discovery News. "The more you look at these, how to deal with them, the more you can refine the techniques."

Stardust collected samples from Comet Wild-2 in 2004, about two years before a part of the spacecraft came back to Earth with samples on board. The spacecraft was a pioneer in sample collection, with only one spacecraft (Japan's Hayabusa, in 2010) doing it since on an asteroid. Hayabusa-2 (in flight now) and NASA's OSIRIS-REx (yet to be launched) plan asteroid sample returns in the coming years.

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One of the biggest surprises of the mission, Brownlee recalled, was finding that at least half the rocky material in the comet was made of materials that were "white-hot" when they were formed. This suggested that the rocky stuff was almost all formed in closer to the sun, and then transported out to the region where Pluto was, where ices formed. It gave a new understanding of our solar system's history.

Another comet mission has been on the mind of the public lately. The European Rosetta mission has been orbiting Comet 67P/Churyumov–Gerasimenko for more than a year, and delivered a lander (Philae) that worked for a few days on the surface. Brownlee said he was sad Philae didn't function for as long as planned, because that was the best way to do direct comparison with Stardust's findings. But Rosetta's gas analysis of 67P is "complementary" to the solids that Stardust brought back to Earth for analysis, he added.

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"Rosetta is a fabulous mission," Brownlee said. "It tells you a lot about the structure and evolution of the comet. But from our perspective, it doesn't tell you much about the origins of the comet."

Besides his Stardust work, Brownlee is working on mission studies for doing a sample return mission from Enceladus — a geyser-spouting icy moon of Saturn — and a second comet-sample mission that would involve a landing.

Originally published on Discovery News.