How do we know if a planet is too light or too dense to be habitable to the life as we know on Earth? Moreover, do exoplanets in the habitable zone have a similar internal structure and chemical composition to that of Earth? I am collaborating with Earth Scientists to answer these questions. The figure below shows the density of about a dozen planets. This is from a nice work (submitted) from Joe Schulze, a graduate student at OSU in the School of Earth Science.
We can then use the following flowchart to determine if the planet is too light or too dense based on a comparison of the core mass fraction (CMF).