Distribution of orbital semimajor axes for S-type planets and binary systems. Here, a₁ denotes the semimajor axis of the S-type planet’s orbit, and a₂ represents the semimajor axis of the binary orbit. More than 720 S-type planets have been identified to date, with transiting planets comprising over half of the sample and predominantly residing at a₁ < 1 au (X. Huang & J. Ji 2022).