The giant planets didn’t always sit where they are today. Our solar system was shaped by a wild and stormy youth.
The dust speck had been plucked from the tail of a comet more than 200 million miles away. Now, under an electron microscope in a basement lab at the University of Washington, its image grew larger, until it filled the computer screen like an alien landscape. Zooming in on a dark patch that looked like a jagged cliff, Dave Joswiak upped the magnification to 900,000. The patch resolved into tiny, jet-black grains. “Some of these guys are only a couple of nanometers in size—that’s amazingly small,” Joswiak said. His tone was reverent. “We think this is the primordial, unaltered material that everything formed from in the solar system.”
The dust speck has a name: Inti, for the Inca god of the sun. It probably spent nearly all of the past 4.5 billion years in a deep freeze beyond Neptune, inside the comet Wild 2 (pronounced VILT-two). Decades ago Wild 2 somehow got nudged into an orbit that drew it in past Jupiter, where it began to disintegrate in the sun’s heat. In January 2004 a NASA spacecraft called Stardust zipped past Wild 2 and snared thousands of dust specks with a trap made of aerogel—a puffy, glassy material that looks like frozen smoke. Two years later a capsule carrying this delicate cargo parachuted into the Utah desert. The Stardust team teased the specks from the gel, stuck them in their electron microscopes, and stared back at the birth of our solar system. They were stunned by what they saw.
Scientists have long known that the planets, comets, and other bodies orbiting the sun were born, some 4.5 billion years ago, from a spinning disk of dust and gas called the solar nebula. They’ve long assumed that things formed more or less where they orbit now. In the frigid realm beyond Neptune, the material available for making comets would have been a mix of ice and fluffy, carbon-rich dust. But Inti’s dark grains contained exotic minerals—hardy bits of rock and metal such as tungsten and titanium nitride that could only have been forged near the newborn sun, at temperatures of more than 3000 degrees Fahrenheit. Some violent process must have hurled them into the outer solar system.
“We were dumbfounded,” says Donald Brownlee, head of the Stardust team and Joswiak’s boss. “It was astounding to find these highest-temperature materials in the solar system’s coldest bodies. The solar system was literally turning itself inside out.”
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