There are at least three aspects of the Solar System that are weird or at least unusual:
- No hot super-Earths. About half of stars contain a planet larger than Earth interior to Venus’ orbit. We don’t have one. That puts us in the minority.
- Jupiter. Only about 15% of Sun-lilke stars appear to have gas giants like Jupiter, and most of these are on very stretched out, “eccentric” orbits. This makes us unusual at the ~5% level.
- Life. Earth is the only planet in the whole freaking Universe that we are sure harbors life. That is pretty awesome, and it makes us extra-special.
Is there a connection between these things? I think so! I just wrote a blog post about it here. Let me summarize the main ideas.
The key question is: how do “hot super-Earths” form? I think that these planets — or maybe just their building blocks — formed farther away from their stars and then were driven inward by the gaseous protoplanetary disk. That process is called orbital migration. It looks something like this:
If one of those migrating planets gets big enough, it can gravitationally attract gas from the disk and become a gas giant planet like Jupiter. Gas giant planets are so massive (Jupiter is more than 300 times more massive than Earth) that they carve ring-shaped gaps in the disk. Any more distant super-Earths that try to migrate inward are blocked by the giant planet:
What this means is that we owe a lot to Jupiter! With no Jupiter, Uranus, Neptune and Saturn’s core may have migrated inward and invaded the inner Solar System! Jupiter is our protector!
A nice feature of this model is that it is testable. We expect an anti-correlation between the presence of Jupiters and hot super-Earths around other stars. This anti-correlation shouldn’t be perfect but it should be there. We’ll find out in a few years!