[gippgig]

news.uchicago.edu/article/2016/03/04/cosmochemists-find-evidence-rare-element-early-solar-system

[Enthalpy]

Thanks!

A few interrogations I have - without having the necessary background:

Why do models for the formation of our solar system suppose that all heavy atoms come from a single supernova nearby? Several events producing separately the chondrites and the siderites would ease many questions.

Why do models suppose that the Solar system started as gas? Does something imply that a supernova explosion produces only gas, including of the heavy and refractory elements, and that the solids appear only when a planetary system condenses?

These two would not need the solids to differentiate in a planet big enough, nor would they need said planet to be destroyed, to explain the diversity of meteorites. Current models have some difficulties with that scheme.

As well, I nearly believe (have check some figures) that gravitation can be extremely efficient at separating elements and isotopes during some stages of the formation of planetary systems. The potential is more than sufficient: at Earth's orbit, one neutron more means about 500 times 300K difference in kinetic energy, so in a gas, the settling would be extremely efficient, much better than anything humans achieve in a centrifuge. The only question is whether at some epoch, the elements exist as a gas, and dilute enough that diffusion is quick.
http://www.physicsforums.com/showthread.php?p=3439127#post3439127
Some observations see oxygen well spread at the very beginning of a planetary system but disappeared at systems but older, which my proposal explains easily.

Such a process would need to re-think the arguments based on isotopic abundance.

[gippgig]

Supernovas are rare; it is less likely that more than 1 happened nearby soon before the solar system formed.
A supernova produces a plasma (and the interstellar medium is also a (very thin) plasma). A particularly dense region of the interstellar medium can collapse due to its own gravity, forming gas and dust, which further collapses to form stars, planets, etc.
I believe there is too much turbulence for isotopic enrichment to occur.

[Enthalpy]

Rare supernovae are an excellent reason, true.

What about dust forming before the protoplanetary system collapses? I haven't checked the figures. Some elements, especially metals, are refractory and their oxides too, so as soon as the temperature and radiation get reasonable again, the atoms must bind at almost every collision.

[gippgig]

I would think that in most cases the density of the interstellar medium is too low for a meaningful number of collisions to occur until some collapse has happened. (I don't think a clear understanding of the process exists yet.)

[Enthalpy]

Yes, that's the point. I'll have to seek a few density figures and check how they combine. Out of lazyness, I had just hoped to get the pre-worked answer. Same for the segregation of elements and isotopes, by the way.