Comet dust yields surprises about universe

University of Washington astronomer Don Brownlee expected surprises from the pinch of comet dust collected by the Stardust spacecraft.

But he didn't foresee such a shake-up.

The tiny specks have changed ideas about the birth of our solar system and offered hints about the origin of life on Earth.

"We're learning incredible things," said Brownlee, principal investigator for the $212 million National Aeronautics and Space Administration (NASA) mission.

Since the capsule parachuted to the Utah desert in January, nearly 200 researchers have employed some of the world's most powerful scientific tools to probe the particles. Their findings are laid out in seven reports in Friday's issue of the journal Science.

Among them is the discovery of organic molecules, very similar to the amino acids that are the building blocks of proteins. The compounds contain a biologically useful form of nitrogen, which would have been important to early microbes.

"The fact that we see these suggests that the presence of amino acids is not an insane idea ... though we haven't detected them yet," said Scott Sandford of NASA's Ames Research Center in California.

The comet dust also contains bits of organic material similar to tar or soot, Sandford said.

The organic molecules bolster the theory that a rain of comet dust may have delivered the basic ingredients of life to the early Earth.

During its seven-year, 2.9 billion-mile voyage, the Stardust spacecraft flew within 150 miles of Comet Wild 2 (pronounced Vilt). Dust surrounding the comet's nucleus was captured in a low-density material called aerogel, like "collecting BBs by shooting them into Styrofoam," Sandford said. The mission marks the first time extraterrestrial material has been brought to Earth since the Apollo moon landings.

The second particle Brownlee and his colleagues pried from the aerogel rocked existing theories of comet birth.

Less than one-fifth the diameter of a human hair, the particle was made up of unusual minerals that were created at blistering temperatures — higher than 2,000 degrees Fahrenheit. But that contradicts the standard view that comets formed on the fringes of the solar system, where temperatures average around minus 400 degrees.

"It was stunning," Brownlee said. "People's jaws dropped."

The finding means material from the hot, innermost reaches of the early solar system was somehow propelled to the frigid nether lands beyond Pluto.

"It's like the solar system partly turned itself inside out," Brownlee said.

Though they weren't forged in such a fiery furnace, crystalline mineral grains in the comet dust also support the notion that there was a lot of mixing in the cloud of dust that coalesced into the solar system about 4.6 billion years ago.

Many experts had expected comets to be composed primarily of interstellar dust, minuscule bits of matter that float through space and originate from stars that have exploded and died. But instead, the comet dust is chock-full of crystals that came from the inner portion of the young solar system.

"It looks like about 10 percent of the material came from the inner disc," Brownlee said. "No one has ever suggested anything like that in the past."

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com