The calcium in your bones and the iron in your blood were once stardust, astronomers like to remind us, but it has been processed many times over. That's a problem for researchers trying to investigate stars and the history of our own solar system, because they would like to find the original stuff in a pristine state, from well before it started coursing through your veins or helping you to walk upright.
So these scientists turn to the freezers of the cosmos, comets, which formed out near the fringes of our solar system and should have scooped up stardust -- tiny particles that were cast into space by other stars back before our Sun was born.
As comets pass through the inner solar system, solar radiation boils away surface material, exposing the primordial dust, the thinking goes. Some of it falls into Earth's atmosphere, and there, in the stratosphere actually, scientists collect it using high-altitude aircraft.
. But silicates, another type of stardust, have remained elusive, even though researchers expect they were plentiful at the time of the solar system's formation and are abundant through the cosmos.A new study reports the discovery of six silicate grains that predate the solar system, bits that were gathered along the solar system's outskirts and transported inward by comets and, finally, collected in the stratosphere while still riding piggyback on larger motes of dust about the size of smoke particles.
One might think the grains will be used to study the stars they came from, but among their most important uses is to provide a glimpse at the formation of this solar system.
"Looking at the chemistry and mineralogy of the stardust tells us a lot about formation processes and conditions in the very early stages of out solar system," said Lindsay Keller of NASA's Johnson Space Center.
Going into the project, Keller assumed his research team, led by Scott Messenger of Washington University in Saint Louis, would find abundant stardust in comet particles.
"In fact, we proposed that many of these particles would consist almost entirely of stardust, but that's not what we observe," Keller said in an e-mail interview. "The results are forcing us to re-evaluate models of comet formation and evolution."
The particles probably were not in space for long before the Sun's birth some 4.6 billion years ago, Keller explained.
"Life is hard for grains in interstellar space and that limits their lifetime," he said. "They get bombarded with cosmic radiation, they get vaporized by interstellar shock waves, and they can be destroyed in collisions. Since the stardust grains were incorporated into comets, they have essentially been in cold storage for the last 4.5 billion years."
The research was published today in the online version of the journal Science.
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