Elegant New Theory Explains Origin Of Asteroid Belt | Hacker News Reader

Elegant New Theory Explains Origin Of Asteroid Belt

technologyreview.com

32 pointsJ3L240412 comments

This theory elegantly explains the structue of one of the known planetary systems, but as far as I can tell forbids the structure of most other known planetary systems which contain at least one "hot jupiter". From a theory that relies on the impossibility of gas giants staying gas giants near a star, I'd expect some arguments as to why all the observed gas giants that are extremely close to their stars do not invalidate it.

Is this just a sloppy writeup, or do they really ignore that?

I suspect a larger hole in this theory is all the "dwarf planet(s)" (ex: pluto) that don't look like small gas giants. I mean nothing prevents a star from capturing a “rogue planet / proto star” and if you look at younger systems you might seem more inner gas giants etc. But, there are several proto planets that don’t seem to fit with the theory.

PS: Then again they could have formed around another star…

From a theory that relies on the impossibility of gas giants staying gas giants near a star, I'd expect some arguments as to why all the observed gas giants that are extremely close to their stars do not invalidate it.

I read the preprint, but it's a little iffy on the idea of how the removal of the outer layers is supposed to work. But I think the idea is that a small gas giant would lose its outer layers if brought in from the outer solar system, while a Jupiter-sized one wouldn't.

Still, the preprint makes no reference to hot Jupiters whatsoever, which seems to be a major oversight. It's no good crowing about how your model explains one planetary system without even mentioning what it says about others.

I don't much like this model, myself.

So planets would tend to form more from the aggregation of gas rather than rocks or dust (then accumulate the other kinds of matter in the new gaseous body). Does this new model also propose that planets formed further out than previously believed? ("in excess of 50au" means further out than Pluto)

If "all the planets rotate in the same direction" because they picked up that momentum from the original cloud, then what happened to Venus? Why does it spin the other way?

This theory picks out one radius, where the belt is, as special. I wonder if it can account for the stable orbits of the other planets too. They're oddly regular. I've always wondered if their arrangement is related in any way to the arrangement of electron shells around atoms, which are also very regular becauuse of the electron energy states.

While retrograde, it's only "weakly" so in that it has a very slow rotation period (1 solar year == 2 solar days).

I think the general theory on Venus is that there was an impact with another body that caused it to start rotating the other way, albeit weakly.

Interestingly enough, astronomy textbooks don't usually refer to Venus as rotating the other way. Rather, they say that it is flipped 180 degrees, which as a result means it rotates the other way.

Does this imply that each of the gas giants has an Earth-like core buried in the gas, surrounded by an orbiting swarm of rocky asteroids?

Because that would be awesome.

"Earth-like" is probably the wrong idea; I'd rather say "rocky". I wouldn't care to guarantee much else about that core would be Earth-like, from the chemistry to the composition to the way it moves or anything else.

Yes, Jupiter and Saturn are currently believed to each have a core of rock and ice, of something like 10-30 Earth masses.

How much time does the planetary core spend inside the embryonic cloud?

It seems like if it spent much time there, it should shows signs of the crushing gravitational pull required for it to maintain a large gaseous atmosphere during birth.

How much time does the planetary core spend inside the embryonic cloud?

The lifetime of the protosolar nebula is pretty short -- only a million years or so.

It seems like if it spent much time there, it should shows signs of the crushing gravitational pull required for it to maintain a large gaseous atmosphere during birth.

I'm not sure what you mean here.

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