The formation of super-Earths and mini-Neptunes with giant impacts

摘要: The majority of discovered exoplanetary systems harbour a new class planets, bodies that are typically several times more massive than the Earth but orbit their host stars well inside Mercury. origin these close-in super-Earths and mini-Neptunes is one major unanswered questions in planet formation. Unlike Earth, whose atmosphere contains less 10 6 its total mass, large fraction planets have significant gaseous envelopes, containing 1 per cent or mass. It has been proposed formed situ either by delivery 50 100M rocky material to inner regions protoplanetary disc, disc enhanced relative minimum mass solar nebula. In both cases, final assembly occurs via giant impacts. Here we test viability scenarios. We show atmospheres can be accreted isolation masses small (typically 3 2 core mass) atmospheric mass-loss during impacts significant, resulting typical postgiant impact 8 4 Such values consistent with terrestrial an order magnitude below inferred for many exoplanets. most optimistic scenario which there no luminosity from and/or planetesimal accretion, find post-giant envelope accretion depleted gas yield If gravitational potential energy last doubling released over dissipation time-scale as luminosity, then reduced about magnitude. Finally that, even absence type I migration, radial drift time-scales due drag shorter lifetimes standard gas-to-dust ratios. Given challenges, conclude observed envelopes larger likely at separations stars.