http://www.physorg.com/news102242467.html

Can the isotopic ratio differences be explained before the formation of planets?

By considering the action of the solar wind on the atomic-scale dust orbiting the the sun, different isotopes would (statistically) be subject to equal wind pressure but their different masses would effectively form a crude natural mass spectrometer.

SongDog, I like your proposal.
Just a little change: Solar wind's pressure is very weak. Radiation pressure is 100-1000 times higher, at least at present days.

As you pointed out, silicon would need to be atomic or condensed in very fine dust so that statistical differences in the isotopic composition allow the radiation pressure to make a difference.

What I like less is that statistical differences in dust size would be much more important than isotopic composition. A silicon gas would be much better... But I know none (SiH4 or worse, SiF4!) under such circumstances.

A simple test could be the isotopic composition of oxygen, since it won't alloy iron, but be sensitive to the same spectrograph effect as silicon.

It's a good idea. But much of the mass of our planet would have been due to asteroids, etc flung into our orbit by Jupiter.

The isotopic composition of silicon isn't very uniform anyway... I looked at the proportions in the solar wind here:
http://umtof.umd.edu/pub/full_spectrum.html
and if I read the diagram properly, it means 29Si is 10% as abundant as 28Si.
Could someone used to these diagrams check it, please?

Though on Earth, the proportion would only be 5%:
http://www.webelements.com/webelements/ele...xt/Si/isot.html

This difference is probably muuuuuuch bigger than the one with Mars, as precise measurements were needed to see it.

So some more explanations arise...
- On Earth, we measure the result of a stronger solar wind that brought more 29Si to the surface of our planet. Rather simple calculations could decide it.
- 29Si was from early stages on more abundant nearer to the Sun and even more in the Sun.

The first alternative explanation would require the Sun to push produced 29Si to its surface, which it doesn't as far as I know.

Does somebody see any hope that Si (or SiO2) may produce SiH4 in a great excess of hydrogen and UV (since early temperatures wouldn't help)? With a gas, simple gravitation could make the isotopic enrichment (before the formation of planets). We're talking about gravity potentials of >30km/s: This is far better than the 500m/s we achieve in uranium separation.

By the way, the higher gravity field of the Earth, not just of the Sun, could also enrich Si in heavier isotopes. It would need an early stage where a gas cloud not too far from a thermal equilibrium surrounds the future planet.