Ceres is the largest object in the asteroid belt, the wide expanse between Mars and Jupiter littered with debris left over from the solar system’s planet-making process. Ceres used to be called an asteroid, but is so large — over 900 kilometers in diameter — that planetary scientists now call it a protoplanet, meaning it was on its way to becoming an actual planet until the raw materials it was growing from ran out. It’s a weird beast. Its interior composition and structure aren’t well understood, but, shockingly, it may have a very briny and possibly muddy liquid water under its surface! When the Dawn spacecraft entered orbit of Ceres in 2015 it immediately saw bright splotches of material in a few craters that turned out to be salt deposits, left over from eruptions of water onto the surface. Also, it spotted one of the weirdest structures in the solar system: Ahuna Mons, a huge Devils Towers-like mesa 17 km wide and looming 4 km above the surface .…