For them to be formed in situ, the super-Earths would have to slowly build up from debris in the "dead zone" of a forming planetary system, known as a protoplanetary disc. This would only happen if there is a lot of turbulence in this area, fueled by magnetism of the surrounding material.
PHOTOS: Epic Auroras Throughout the Solar System
"The size of the dead zone must be large enough that it lasts for the entire disc lifetime," Martin added. "Since different systems may have different dead zone sizes, formation in the inner parts may not be possible in all systems and thus both formation locations may be operating."
Of the super-Earths that have been observed, the researchers noted two distinct types depending on their density. They conclude that planets that form farther out in the disc would be less dense, since water and other volatiles will freeze out in the cooler outer parts of the disc. Those that are closer one would be denser.
PHOTOS: Top 10 Astronomical Discoveries Of All Time
So what about our own solar system? The researchers speculate that here, super-Earths formed in situ and swept up all the material inside of Mercury's orbit. "If the disc is sufficiently cool, the migration timescale for them to fall into the sun is short enough for this to happen in the lifetime of the disc," Martin said. But more research will be needed to confirm this.
The research was accepted for publication in the Astrophysical Journal, and is now available in preprint version on Arxiv.