These planets all have very short orbital periods, between 9 and 55 days. By Kepler’s third law (p^2 ~ a^3), we know that these planets are all very close to th

These planets all have very short orbital periods, between 9 and 55 days. By Kepler’s third law (p^2 ~ a^3), we know that these planets are all very close to their star. Much closer than Mercury is to the Sun (p ~ 116 days). Their close proximity leads to gravitational interactions when they pass by one another. This gradually leads to a very stable orbital resonance due to constructive interference.