The Rule of Planets in Solar Systems

Interesting!:

The pattern I found on that sunny afternoon: planets in the same system tend to be the same size. For example, if one planet is 1.5 times the radius of Earth, the other planets in the system are very likely to be 1.5 times the radius of Earth, plus or minus a little bit.

This is not at all what my colleagues and I expected. In our solar system, planets range from the size of Mercury (less than half the radius of Earth) to Jupiter (more than ten times the radius of Earth). The whole population of exoplanets discovered by Kepler ranges from one quarter the size of Earth to about twenty times the size of Earth. Yet, despite this wide range of possible sizes, planets tend to be about the same sizes as their neighbors. One of my collaborators decided they looked like “peas in a pod,” and that moniker became our shorthand for the pattern.