They found that planets in the same planetary system have correlated sizes. “Each planet is more likely to be the size of its neighbor than a size drawn at random from the distribution of observed planet sizes,” the paper said. If the system contains three or more planets, the planets are also more likely to be spaced regularly. Smaller planets seem to sit closer together than larger planets, leading scientists to believe that the patterns developed early during their formation.
This is at odds with our Solar System, Weiss explained to The Register. “Unlike these exoplanetary systems, the solar system has incredible size diversity. Earth is more than twice the radius of Mercury, Neptune is four times the radius of Earth, and Jupiter is ten times the radius of Earth. Also, the terrestrial planets are very widely spaced.”
The authors suggested the complex gravitational interactions between Jupiter and Saturn are to blame. When the terrestrial planets were still forming, Jupiter and Saturn scattered the protoplanets and increased the number of collisions among them.