On the low-mass planethood criterion

We propose a quantitative concept for the lower planetary boundary, requiring that a planet must keep its atmosphere in vacuum. The solution-set framework of Pec˘nik and Wuchterl [2005. Giant planet formation. A first classification of isothermal protoplanetary equilibria. Astron. Astrophys. 440, 1183-1194] enabled a clear and quantitative criterion for the discrimination of a planet and a minor body. Using a simple isothermal core-envelope model, we apply the proposed planetary criterion to the large bodies in the Solar System.