- National Geographic News: “Comet Built Like an Asteroid, Scientists Find”
The Stardust mission retrieved samples of the comet Wild 2 for NASA, bringing them back to earth in 2006. Studies of these samples are overturning previous thinking on what comets are and where they come from, National Geographic News explains.
“The first surprise was that we found inner solar system materials, and the second surprise was that we didn't find outer solar system materials.”
Although Wild 2 orbits like a comet, a chemical analysis by scientists indicates that the comet’s composition is asteroidal, resembling objects from the inner solar system’s famous asteroid belt rather than “pristine and ancient materials expected to be deep-frozen in the much more distant Kuiper Belt.”
“The first surprise was that we found inner solar system materials, and the second surprise was that we didn't find outer solar system materials,” explained study leader Hope Ishii, a physicist at the Lawrence Livermore National Laboratory.
Some astronomers believe this analysis confirms computer models that show “a major shake-up in the formation of the solar system that would have scattered materials far and wide—causing, for instance, inner solar system materials to reach the outer solar system.” Astronomers add that Wild 2 couldn’t have always been in the inner solar system, or it would have lost all of its dust and ice and not-so-melodramatically faded into oblivion.
Disappointed astronomers are pondering theories as to why Wild 2 contained none of the “pristine samples that predate the solar system,” which was part of the motivation for the Stardust mission (hence its name), as the team explained:
81P/Wild 2 has been widely anticipated to be a reservoir of presolar material, including stardust, cryogenically preserved since the accretion of the planets.
National Geographic News adds, “The researchers thought they would detect ancient stardust that collapsed to form our own sun and planets.” Ishii claims such ancient comets must exist because airplanes in the earth’s atmosphere have collected their dust.
Of course, the reason astronomers object to the idea that comets could be located within our solar system is their assumption about the age of the solar system (and, thus, the amount of time comets would have been exposed to sunlight). Viewing the solar system through a young-age lens makes the “problem” of the missing ancient comet dust disappear.
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