Comet samples returned to Earth by a NASA mission are forcing scientists to revise their ideas about the comet they sent it to.

Comets are thought to form out in the suburbs of the solar system, and researchers expected the Stardust mission to Wild 2 to return with samples of the “pre-solar” dust that would have been found out there. Hence the name.

Boy were they wrong – Wild 2 has a composition more like that of an asteroid and the researchers found material characteristic of the inner solar system, according to research published in Science.

“The material is a lot less primitive and more altered than materials we have gathered through high altitude capture in our own stratosphere from a variety of comets,” says study author Hope Ishii (press release). “…It’s a reminder that we can’t make black and white distinctions between asteroids and comets. There is a continuum between them.”

“For those of us who study presolar materials, it’s turned out to be a bit of a bust,” cosmochemist Larry R. Nittler told Science’s Dick Kerr. At the same time Kerr quotes John Bradley of Lawrence Livermore saying “The mission’s been a huge success. It’s changing the way we think about comets.”

The LA Times goes for the drama (needs registration): “NASA’s Stardust upends comet theory”. The SF Chronicle goes with the slightly less radical “Bits of comet surprise scientists”.

“Wild 2 is more on the asteroid end of the spectrum—more asteroid-like than cosmically primitive comets,” Ishii says on the National Geographic. “We know there have to be comets that are on the more pristine end of it. We’d sure like to go out to one of those.”

No one seems to be asking whether Wild’s asteroidal proclivities might have been predictable, or whether there might have been other targets better able to supply the mission’s eponymous objective

Image: stardust capsule returns to Earth, as seen from DC-8 Airborne Laboratory / NASA