A little media storm has broken out about possible contamination of the Stardust comet samples – it’s been claimed that osbornite, one of the high-temperature minerals found in Stardust’s detectors, was not from the comet at all, but from the probe’s fuel source – a possiblilty which the Stradust scientists say they have already ruled out (the Nature story linked to above contains quotes and discussion from both sides).
For those of you wondering why the presence or absence of this mineral in a comet is so important, I give you a repost from ye olde blog:
Via the BBC: NASA has just released some preliminary results from the Stardust probe [doi for eventual Science paper], which brought dust particles from Comet Wild-2 back to Earth in January. Intriguingly, it seems that a significant proportion of the material collected consists of minerals, such as olivine and other silicate minerals, which only form at temperatures >1000 C.
Back when the probe first landed I explained how examining the composition of the cometary material could help to constrain our models of planetary formation. What these results may be telling us is that the planetary nebula which eventually formed our solar system was a much more dynamic place than we have supposed up to now. From the NASA press release:
“We have found very high-temperature minerals, which supports a particular model where strong bipolar jets coming out of the early sun propelled material formed near to the sun outward to the outer reaches of the solar system,” said Michael Zolensky, Stardust curator and co-investigator at NASA’s Johnson Space Center, Houston. “It seems that comets are not composed entirely of volatile rich materials but rather are a mixture of materials formed at all temperature ranges, at places very near the early sun and at places very remote from it.”
In the model referred to (known as the “X-wind model” – see here for some background), the “strong bipolar jets” are thought to be generated by the interaction of a rapidly spinning accretion disk with the magnetic field of the growing central protostar. This model was originally proposed to explain similar mixing of material which formed at different temperatures (and therefore locations) in asteroids, but the fact that we are seeing material from the very inner solar system being transported right out into the outer reaches where comets formed means that these jets must have been very powerful indeed.
As always, of course, there is another alternative – this material might predate the solar system. Having formed close to another, older, star, it was blown into interstellar space by a supernova, and then incorporated into the planetary nebula which eventually became our solar system. Measuring some isotopic ratios for these grains should help to distinguish between these two possibilities.
Addendum
While preparing this repost I also came across an interesting recent story at NASA’s Stardust site. Only the capsule containing the Aerogel detectors returned to Earth, with the Stardust probe itself continuing on back into the solar system once it had released them. It’s apparently still alive, and they’re considering redirecting it the way of Comet Tempel-1, the object of Deep Impact’s attentions, to image the crater and see what other changes have taken place. That would be pretty cool…
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