On the structural law of exoplanetary systems Available to Purchase

The major semiaxes of the planets in our Solar system obey a simple geometric progression known as the Titius-Bode law, whose physical origin remains disputed. It was recently shown that the five planets in the exoplanetary system 55 Cancri follow a similar (but not identical) progression of the form a_n α e^bn . Here, we show that the other ten systems (υ And, Gliese 876, μ Ara, Gliese 581, KOI-730, HR 8799, Kepler-20, Kepler-33, HD 10180, and Kepler-11) currently known to harbor four or more planets also obey such a structural law. Interestingly, the parameter b is similar in all systems with values between 0.2 and 1.32. This similarity suggests that the structural law might be related to a dynamical relaxation process rather than to the physical conditions in the original proto-planetary disks.