The Mass Distribution of Transit Exoplanets from the Mass–Radius Relationships: the Structurization within Planetary Systems
2021
Most transit exoplanets (85%) were discovered with the Kepler space telescope. However, the mass, which was measured mainly with the radial velocity method, is known only for ~15% of them. The mass of an exoplanet may be estimated by its radius from the statistical dependences based on the observational data, though no unambiguous interrelation between the mass and the radius of planets exists. Here, we calculate the earlier unknown masses of exoplanets from four statistical mass–radius relationships (Bashi et al., 2017; Chen and Kipping, 2017; Ning et al., 2018, and the averaged dependence derived) and added the results to the distribution of planets with known masses. The mass distributions of transit exoplanets obtained in this way are analyzed with taking into account the observational selection effect inherent in the transit method. The distributions are approximated by the power law ∂N/∂M ~ Mα, where the exponent (α < 0) is determined by the maximum likelihood estimation for the samplings acquired with four mass–radius relationships: α = –2.12 ± 0.03, –2.09 ± 0.03, –1.94 ± 0.03, and –2.27 ± 0.04. Moreover, for one of these distributions, we determine the parameters of the power law, the exponent of which differs on three intervals (with the boundaries at 0.025, 0.28, and 1.34 Jupiter masses): –1.99, –0.62, and –2.88. We also conclude that there is no evidence of the interrelation between the mass of an exoplanet and its average distance to the host star (the structurization within planetary systems), if this distance is smaller than 1 AU; besides, the dependence of the exponent α on the considered mass interval is analyzed. The above estimates appertain to exoplanets detected by the space telescopes: Kepler Space Telescope and Transiting Exoplanet Survey Satellite (TESS) (these exoplanets compose group 1). The masses of the other transit exoplanets, which were detected by ground-based instruments, were known (they compose group 2). For the latter group, the exponent α is estimated at –2.21 ± 0.04. In general, the results of our analysis agree with those of the earlier statistical and theoretic studies. A key idea of the present paper is to apply the model interrelations between the mass and the radius of exoplanets to the analysis of the mass distribution of exoplanets on the basis of the recent data of observations.
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