PDA

View Full Version : Cooking Up Comet Crystals



A.DIM
2009-May-21, 01:01 PM
From [http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=3141&mode=thread&order=0&thold=0]Astrobiology Magazine[/url]:

Scientists have long wondered how tiny silicate crystals, which need sizzling high temperatures to form, have found their way into frozen comets, born in the deep freeze of the solar systemís outer edges. The crystals would have begun as non-crystallized silicate particles, part of the mix of gas and dust from which the solar system developed.

...

"We believe that we have observed, for the first time, ongoing crystal formation," said one of the paperís authors, Attila Juhasz of the Max-Planck Institute for Astronomy in Heidelberg, Germany. "We think that the crystals were formed by thermal annealing of small particles on the surface layer of the starís inner disk by heat from the outburst. This is a completely new scenario about how this material could be created."

A.DIM
2009-May-21, 01:02 PM
Ooops, I just realized this should probably be in "Astronomy" ...

trinitree88
2009-May-21, 02:09 PM
A. Dim. Interesting. Silicate grain growth should also be enhanced by Ostwald ripening. It's a statistical effect whereby evaporation from a solid (actually sublimation).. or liquid phase enables particles, (molecules or atoms) to travel through a vapor phase, and then redeposit elsewhere (condense or resublime). Statistically, it is more likely that the particle will land on the surface of a large particle than a smaller one, so every time the process happens, the big ones grow and the little ones disappear. Flash heating can greatly increase the effect by increasing the vapor phase pressure. One would expect not only the annealing the authors suggest, but transport of vaporized silicate from regions closer to the star, where it's too hot for grains, to the disk's edge.

Found a neat little video, of a SIMILAR effect, not silicate, click on the Prof's video animation, and see the metal drops both disappear & grow....smile professor:shifty: thanks, pete use A Flash movie 6.0...

see:http://www.phys.huji.ac.il/~meerson/

Swift
2009-May-21, 02:11 PM
Ooops, I just realized this should probably be in "Astronomy" ...
So let it be written, so let it be done. :D

Very interesting article

I would not be surprised if all these different mechanisms could contribute. I also agree with trinitree88's idea of Ostwald ripening.