Classification of planets and estimation of interior properties based on primary parameters

Classification is an essential method and has been developed and applied in astronomy for over onehundred years. However, the planet, still lack a universal classification method, mainly because thesample of the planet is too small to perform statistical analysis. Fortunately, nowadays, exoplanetssupply a large sample to support building a classification framework. In this study, we select 1M⊙systems as representative samples based on the exoplanet survey results. And use the numericalsimulation data to overcome the selecting effect in observation. In our analysis, planets are classifiedinto four main categories (giant, compact, puffy, terrestrial) with the mass divide line around 100M⊕. According to the evolution traces of all the planets, many relations are obtained. Giant planetsstrongly rely on low-density embryos, and compact planets are shown as the temporary category inthe formation of the giant planets, they should be the solid core of the giant planet. By analyzing themass-radius relation for the giant planets, a radius turning point is found at 3.9 MJ , which correspondsto the maximum size that cool giant planets can sustain. With the help of the interior model, we foundthat compact planets still hard to form an electron degeneracy core, but some of them are very close. Inthe low-mass region, using the structure model via the SMINT code, we discover two types of planetswith different gas envelope mass fractions fenv in ≥ 4.5g/cm3 region (≤3% and 10%) and one typein ≤ 4.5g/cm3 region (10-20%). Under the two-layers assumption, we calculate both maximum andminimum core radius fractions (CRF) for low mass region planets and the true planets from observationwith the hardCORE code. Obtain the pure-core structure boundary at 30 g/cm3 for dense planets inobservation, and the maximum CRF around 5.5 g/cm3 for non-dense planets in simulation. Besides,the 4 and 6 g/cm3 are the critical densities for a dense core and low-density component inside theplanets. Though there are still many details need to be settled, we build up a simple classificationframework for planets, and speculate on some interior properties of them. With the help of thisframework, we can easily find the potential evolution path and interior structure of a given planet.