Solar system formation Options

[dvandorn]

Here is a recent article in space.com (I tried to link to this a few days ago, but it disappeared from the space.com archives...today it's back) about how Jupiter may have a much bigger core (14-16 Earth masses of rock!) than previously proposed. Previous predictions ranged from a core of 7 Earth masses of rock to no core at all. Juno should help nail down the absolute size of the core, and therefore, whether a rock core was required for the initial accretion.

Which came first: gas or rock?

And if rock is required to initiate accretion of gas giants... what about stars?

-the other Doug

(This discussion was originally in the Juno thread but was moved to a separate topic - moderator)

[dvandorn]

I think some kind of plasma form for the rocky core is most likely, by the time a star ignites. But the natural process of gravity is such that the heaviest elements in the molten rocky core (prior to its plasma-ization) would have settled in the very center, the core of the core, so to speak. The lighter elements, the silica and iron and aluminum, et. al., would have formed shells around the presumed nickel-iron-uranium-etc. core.

As such a highly differentiated core is pummeled by the energy of its immediate "atmosphere" fusing around it, it would dissociate into atomic forms, I imagine, but at those incredible temperatures and pressures, and with that many photons trying to force their way into the heavy element mass, you'd think that generally symmetrical pressures all around would keep the heavy elements in the center.

Now, if there is *turbulence* in the fusing atmosphere around the heavy elements, uneven or patterned flow of fusing plasma around the core, it could possibly be eroded, great hunks of heavy elements being picked up and tossed higher into the gas plasma. But being heavier, you'd think that even in the seething energy environment, they'd still evenutally sink back down to the center.

Also, as a star ages, more and more of its mass is made up of helium, the fused by-product of hydrogen fusion. The helium is heavier than the hydrogen, and sinks down toward the core, where the very high temperatures and pressures cause the helium to fuse, making lithium. The lithium continues to sink, and at some point it fuses, on through a process that creates elements as heavy as iron. So the star is slowly forming even more heavy elements, which I would imagine would sink and collect around the original heavy-element core.

So, even though you might think that a rocky stellar core might just be vaporized, and you'd be sort of correct, in the conditions at a stellar core the vapor would have nowhere else to go but to be compressed and sink back into the center of the core. And as the star gets older, it creates more and more heavy elements until the original heavy element abundance has increased greatly.

Of course, when the star is big enough, its rapid expansion as the last of the hydrogen is used up and the associated sudden light pressure release blows the star apart. The explosion occurs *between* the core and the surface of the star, though, causing an equally forceful implosion that blasts the heavy-element core so hard as to make iron fuse, and heavier elements fuse, creating the true heavy elements, and another supernova seeds clouds of gas with even more raw materials for new stars, planets and moons.

The really interesting information we might be able to extrapolate from Juno data is the dynamics of the core. The temperatures and pressures at the core of Jupiter may well be enough to have caused any rocky core it once had to have settled into a differentiated heavy element plasma ball. Understanding those dynamics would be very enlightening in extrapolating to the later phases of stellar core evolution about which I have been speculating above.

-the other Doug

[stevesliva]

I can't speculate, but some people have:
http://adsabs.harvard.edu/abs/1988Ap&SS.144..519R