Kepler-10b is a rocky, dense and hellish planet just 1.4 times the size of Earth. It’s not in the Goldilocks zone, orbiting much too close to its star for life to exist. It’s so hot (about 2,500 degrees F at the surface) that boiled iron and silicates are flowing into the stellar wind, much like a comet’s tail. Kepler-10b is more than 20 times closer to its star than Mercury is to the sun, and it whips around the star once every 0.84 days. Its average density is comparable to that of an iron dumbbell, says NASA — about 8.8 grams per cubic centimeter, or 0.32 pounds per cubic inch.