The most common type of planet in the galaxy may not look anything like Earth on the inside

We have learned a lot about the planets in our own backyard, and for a long time we assumed the rest of the galaxy looked roughly the same. A rocky planet meant a clear-cut structure: a dense metallic core, a silicate mantle, and a thin atmosphere on top. That picture works fine for Earth. But according to a new paper submitted to the Astrophysical Journal, it might not work for most of the rocky planets in the universe. …