Diversities and similarities exhibited by multi-planetary systems and their architectures: II. Radii of singles and multis

Artikel i vetenskaplig tidskrift, 2026

The discovered planets in apparent single-planet systems (hereafter singles) and those in systems with multiple detected planets (hence-forth multis) exhibit a rich diversity of physical and orbital properties. However, it is still debated whether the observed singles and multis originate from the same underlying planet population. We investigate the differences and similarities between 1730 singles and 1522 multis in a catalogue of confirmed transiting planets orbiting main-sequence stars with spectral classes ranging from late-M to late-F. After we removed the hot Jupiters, the planet types and their fractional numbers were similar for the multis and singles hosted by FGK-type stars. Furthermore, the median radii of both the singles and the multis increase with host star temperature already from late- to early-type M dwarfs and further up to F stars. Our analyses show that the singles are larger on average than the multis in our F, G, K, and M samples. However, after we excluded the hot Jupiters, the radius distributions of the singles and multis orbiting FGK stars are statistically indistinguishable, particularly at R < 4 R-circle plus. In the FGK sample, we also identified an unexpected and significant overabundance of multis, compared to singles, at radii of approximate to 1.4-1.6 R-circle plus. For the early- and late-type M samples, our work indicates that the multis are smaller on average than the singles and that the radius distributions of the multis and singles are different, except for the planets with R < 4 R-circle plus hosted by early-type M dwarfs. Nevertheless, these results for the two M samples are inconclusive because the sample sizes of 167 and 101 planets are limited. In conclusion, our analyses reveal that the singles and multis, excluding the hot Jupiters, orbiting FGK stars are overall consistent with originating from the same underlying population based on their planet types and radii. This interpretation is, however, not applicable within the region of the overabundance of multis at approximate to 1.4-1.6 R-circle plus identified in this work, which is an intriguing feature warranting further investigations.