Is there a way for a rocky planet thats roughly earth-like in mass and composition to form or be thrown into a stable orbit as a planet proper, and not become a moon of one of the gas giants?
First, I just took a look in the list of known multiplanery systems, and ordered by the number of planets in a descending order.
I didn't need to go very far down on the list to find these:
- b: Rocky, but unconfirmed
- c: Either gas giant or gas dwarf
- i: Rocky, but unconfirmed
- d: Either gas giant or gas dwarf
- e: Gas giant
- j: Very likely a rocky superearth, but unconfirmed
- f: Gas giant
- g: Gas giant
- h: Gas giant
I.e., planets i and j are possibly what you are looking for.
- b: Probably a gas dwarf
- c: Likely a gas dwarf
- d: Superearth
- e: Gas giant
- g: Gas giant or gas dwarf
- f: Gas giant
I.e., planet d definitely is what you are looking for.
This is very poorly constraint, but all the 6 planets are in the middle ground of superearths or gas dwarfs.
A possible scenario is that 4th and the 6th planets are gas dwarfs, and the 5th is a superearth, hence what you are looking for.
However, a more likely scenario is that the 5th is also a gas dwarf, thus, not what you are looking for.
- b: Probably a rocky superearth, but possibly a gas dwarf
- e: Rocky, Venus-like
- c: Probably a gas dwarf
- f: Rocky, Earth-like
- g: Gas giant, unconfirmed
- d: Gas giant
I.e., planet f and perhaps e would be what you are looking for.
- b: Almost certainly a superearth. Unlikely, but possibly, a gas dwarf.
- c: Probably a superearth, possibly a gas dwarf.
- d: Likely a gas dwarf. Unlikely, but possibly, a superearth.
- e: Surely a gas dwarf.
- f: Probably a superearth. Unlikely, but possibly, a gas dwarf.
- g: Almost certainly a gas giant.
There are 6 planets, By mass, there is a fair possibility that the 1st and the 5th are actually superearths and then the 5th would be what you are looking for.
However, further data including density says that all of them would be gas dwarfs. But since the data is very poorly constrained and we also have very poor knowledge about superearths and gas dwarfs, then we really don't know yet what is going on.
5 planets, but their masses are poorly constrained. The last is definitely a gas giant. The 4th is either a gas dwarf or a gas giant.
It is possible that the 2nd and the 3rd are superearths while the 1st is a gas dwarf.
5 planets, but their masses and radius are very poorly constrained, so we really don't know for sure. But it seems that the 1st and the 5th are rocky, the 2nd and 4th are gas dwarfs and the 3rd either a superearth or a gas dwarf.
5 planets. Accordingly to whoever edited this article on wikipedia, one of them is rocky and the other 4 are gas giants, but the article doesn't says which one is rocky. Looking to the planetary system table there, I think that the 3rd would be the rocky planet.
4 planets. The 1st is a superearth. The 2nd and the 4th are gas giants. The 3rd might be either a superearth or a gas dwarf.
Superearths between gas dwarfs!? Meh, what about Earth-sized between Jupiter-sized?
None known as far as I can tell. We don't know those yet because:
- a. Those might be very rare.
- b. Detecting Earth-sized or Mars-sized exoplanets is incredible hard and very few of those are known.
- c. Most of the known exoplanets are very near to their host stars because our detection methods perceive them much easier than those far away, and this introduces a severe observational bias.
- d. Very few exoplanets were directly photographed, and all of those are very large gas giants in wide orbits. So, if there are rocky planets orbiting between them, we just don't know yet.
As we are studying and discovering more and more about stellar systems other than the Sun's, more and more we discover that a large part of them deviates a lot from what we expected from our planet-formation theories. And just 30 years ago, we knew nothing about them, so it might be just a matter of time and luck until we look to the right star and find a system that is what you are looking for, and possible one of those listed above is exactly that, just waiting for better-constrained data.
A possible scenario is that in a thick part of the formation disk, three planets starts to form, one in the inner side but still somewhat far from the inner edge, one right in the middle, and one in the outer side, but also far from the outer edge. Then, the inner and the outer planets starve the middle one from forming material, but not enough to prevent the formation of a rocky planet there. Also, it is important that the inner planet don't migrate outward after being formed nor that the outer migrate inward (the opposite is ok).