55 Cancri e is a super-Earth twice the size of our planet, but it’s not your typical rocky world. Because of its extreme heat and carbon-rich composition, scientists believe it could have a diamond crust. The pressure inside would be so intense that carbon crystallizes, creating a literal gem of a planet. If true, its surface could be shimmering with graphite and diamond—though at 2,400°C (4,400°F), you wouldn’t want to go mining there.