  We explore in situ formation and subsequent evolution of close-in
super-Earths and mini-Neptunes. We adopt a steady-state inner protoplanetary
gas disc structure that arises from viscous accretion due to the
magneto-rotational instability (MRI). We consider the evolution of dust in the
inner disc, including growth, radial drift and fragmentation, and find that
dust particles that radially drift into the inner disc fragment severely due to
the MRI-induced turbulence. This result has two consequences: (1) radial drift
of grains within the inner disc is quenched, leading to an enhancement of dust
in the inner regions which scales as dust-to-gas-mass-flux-ratio at ~1 AU; (2)
however, despite this enhancement, planetesimal formation is impeded by the
small grain size. Nevertheless, assuming that planetary cores are present in
the inner disc, we then investigate the accretion of atmospheres onto cores and
their subsequent photoevaporation. We then compare our results to the observed
exoplanet mass-radius relationship. We find that: (1) the low gas surface
densities and high temperatures in the inner disc reduce gas accretion onto
cores compared to the minimum mass solar nebula, preventing the cores from
growing into hot Jupiters, in agreement with the data; (2) however, our
predicted envelope masses are still typically larger than observed ones.
Finally, we sketch a qualitative picture of how grains may grow and
planetesimals form in the inner disc if grain effects on the ionization levels
and the MRI and the back-reaction of the dust on the gas (both neglected in our
calculations) are accounted for.
