There seems to be an emerging maxim in deep space studies: every new mission will overturn at least one enshrined assumption Thus the early Stardust results, studying the cometary debris from Wild 2. Because comets come out of the outer dark in their long arc toward the inner system, one would expect them to be made of materials that were born in cold temperatures. But Stardust has brought us cometary dust that’s packed with minerals formed at high temperatures.
What a fascinating set of challenges now face the Stardust researchers. They’ve found olivine in the Wild 2 materials; it’s a compound of iron, magnesium and various other things (the Stardust sample is primarily magnesium). Most astronomers believe that olivine crystals are formed from glass that has undergone heating near stars. So how crystals of olivine can show up in the Wild 2 samples bears scrutiny — after all, Wild 2 is thought to have formed well beyond the orbit of Neptune.
And olivine isn’t the only oddity about the Stardust samples. They also contain high-temperature minerals that are rich in calcium, aluminum and titanium. The message seems clear, as stated by principal investigator Donald Brownlee (University of Washington): “I would say these materials came from the inner, warmest parts of the solar system or from hot regions around other stars.”
About 150 scientists around the world are working on the Stardust samples. They’re studying grains that are embedded in the aerogel used to trap them during the mission’s encounter with the comet in January of 2004. And there’s no shortage of material to work with, since thousands of cometary grains are now available. Brownlee notes that his laboratory has worked on only two particles so far, and has yet to cut into the main part of the first of them.
Centauri Dreams‘ take: We now have samples from the farthest regions of the Solar System that were clearly formed at high temperatures. So perhaps we’re looking at a formation mechanism for planetary systems that involves a constant flow of materials from the center to the outer regions. Or — and this is just as interesting a possibility — it may be that cometary materials like these actually came from other solar systems through transfer mechanisms yet to be explained. Much remains to be done, especially with regard to possible organic materials in the Stardust grains. The payoff just might be a revision of key planetary formation theories. We’ll keep a close eye on this one.