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We explore in situ formation and subsequent evolution of close-insuper-Earths and mini-Neptunes. We adopt a steady-state inner protoplanetarygas disc structure that arises from viscous accretion due to themagneto-rotational instability (MRI). We consider the evolution of dust in theinner disc, including growth, radial drift and fragmentation, and find thatdust particles that radially drift into the inner disc fragment severely due tothe MRI-induced turbulence. This result has two consequences: (1) radial driftof grains within the inner disc is quenched, leading to an enhancement of dustin 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 thesmall grain size. Nevertheless, assuming that planetary cores are present inthe inner disc, we then investigate the accretion of atmospheres onto cores andtheir subsequent photoevaporation. We then compare our results to the observedexoplanet mass-radius relationship. We find that: (1) the low gas surfacedensities and high temperatures in the inner disc reduce gas accretion ontocores compared to the minimum mass solar nebula, preventing the cores fromgrowing into hot Jupiters, in agreement with the data; (2) however, ourpredicted envelope masses are still typically larger than observed ones.Finally, we sketch a qualitative picture of how grains may grow andplanetesimals form in the inner disc if grain effects on the ionization levelsand the MRI and the back-reaction of the dust on the gas (both neglected in ourcalculations) are accounted for.

Close-in Super-Earths: The first and the last stages of planet formation in an MRI-accreting disc