As Earths go, there are generally two types: the happy-go-lucky, human inhabited kind and the slightly larger exoplanets we've termed super-Earths. Super-Earths get their name from their rocky surfaces and the way they dwarf our own planet. These super-Earths weigh in at somewhere in the neighborhood of twice that of our home world, a sweet spot that science tells us is just below the threshold for the creation of a gas planet. With Neptune as evidence, the theory looked, er, solid — that is until Kepler-10c broke the mold.
Discovered back in 2011 by the Kepler spacecraft, Kepler-10c was originally thought to be just another far-flung version of Neptune. On closer inspection, what Kepler-10c seems to be is, as Smithsonian researcher Dimitar Sasselov calls it, "the Godzilla of Earths!" Weighing in at 17 times the mass of Earth, Kepler-10c is the first ever known Earth-like planet to defy the super-Earth classification. It is, in fact, a mega-Earth.
Despite its overwhelming size, Kepler-10c actually has more in common with Earth than a rocky surface. Due to its huge size, scientists believe that Kepler-10c is too big to have lost any atmosphere it has ever had. That means that the massive rocky world is not the stripped core of a once-gassy planet. It also means that Kepler-10c could support life. As Sasselov puts it "if you can make rocks, you can make life."
Positive implications aside, whatever life could exist on Kepler-10c, it won't look a lot like us. The planet's immense gravity, as well as its blindingly quick 45-day orbit around its star, would wreak havoc with human bodies. With Kepler-10c 560 light-years away in the Draco constellation, we'd have to work pretty hard to get there anyway. That might be for the best, because whatever life exists on Kepler-10c has had the last 11 billion years to evolve. In short: Kepler-10c could be a very real Krypton, populated by super-evolved beings that can resist immense gravitational forces. Then again, it could simply be the home of some weird looking bacteria.