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  • An overabundance of low-den...
    Cubillos, Patricio; Erkaev, Nikolai V; Juvan, Ines; Fossati, Luca; Johnstone, Colin P; Lammer, Helmut; Lendl, Monika; Odert, Petra; Kislyakova, Kristina G

    Monthly notices of the Royal Astronomical Society, 04/2017, Letnik: 466, Številka: 2
    Journal Article

    We present a uniform analysis of the atmospheric escape rate of Neptune-like planets with estimated radius and mass (restricted to M sub( p) < 30 M...). For each planet, we compute the restricted Jeans escape parameter, ..., for a hydrogen atom evaluated at the planetary mass, radius, and equilibrium temperature. Values of Lambda ... 20 suggest extremely high mass-loss rates. We identify 27 planets (out of 167) that are simultaneously consistent with hydrogen-dominated atmospheres and are expected to exhibit extreme mass-loss rates. We further estimate the mass-loss rates (L sub( hy)) of these planets with tailored atmospheric hydrodynamic models. We compare L sub( hy) to the energy-limited (maximum-possible high-energy driven) mass-loss rates. We confirm that 25 planets (15 per cent of the sample) exhibit extremely high mass-loss rates (L sub( hy) > 0.1 M... Gyr super( -1)), well in excess of the energy-limited mass-loss rates. This constitutes a contradiction, since the hydrogen envelopes cannot be retained given the high mass-loss rates. We hypothesize that these planets are not truly under such high mass-loss rates. Instead, either hydrodynamic models overestimate the mass-loss rates, transit-timing-variation measurements underestimate the planetary masses, optical transit observations overestimate the planetary radii (due to high-altitude clouds), or Neptunes have consistently higher albedos than Jupiter planets. We conclude that at least one of these established estimations/techniques is consistently producing biased values for Neptune planets. Such an important fraction of exoplanets with misinterpreted parameters can significantly bias our view of populations studies, like the observed mass-radius distribution of exoplanets for example. (ProQuest: ... denotes formulae/symbols omitted.)