Classifying Worlds

Is there a way to naturally classify the different types of planets in the Universe? Two of the most fundamental properties of any object are its mass and size and generally one expects size to increase as we add more mass. The relationship between size and mass itself changes though at certain points, and this offers a clear way to classify worlds. Graduate student Jingjing Chen of the Cool Worlds Lab discusses one component of her new paper which does just this, classifying planets based off their mass and size and concluding that just four broad categories of planets...