  We first consider how the level of turbulence in a protoplanetary disk
affects the formation locations for the observed close-in super-Earths in
exosolar systems. We find that a protoplanetary disk that includes a dead zone
(a region of low turbulence) has substantially more material in the inner parts
of the disk, possibly allowing for in situ formation. For the dead zone to last
the entire lifetime of the disk requires the active layer surface density to be
sufficiently small, <100 g/cm^2. Migration through a dead zone may be very slow
and thus super-Earth formation followed by migration towards the star through
the dead zone is less likely. For fully turbulent disks, there is not enough
material for in situ formation. However, in this case, super-Earths can form
farther out in the disk and migrate inwards on a reasonable timescale. We
suggest that both of these formation mechanisms operate in different planetary
systems. This can help to explain the observed large range in densities of
super-Earths because the formation location determines the composition.
Furthermore, we speculate that super-Earths could have formed in the inner
parts of our solar system and cleared the material in the region inside of
Mercury's orbit. The super-Earths could migrate through the gas disk and fall
into the Sun if the disk was sufficiently cool during the final gas disk
accretion process. While it is definitely possible to meet all of these
requirements, we don't expect them to occur in all systems, which may explain
why the solar system is somewhat special in its lack of super-Earths.
