Frost and Fire
In the constellation of Leo 33.1 light years away, a Neptune-sized planet orbits a red dwarf star at a distance of 4.3 million kilometres—15 times closer than Mercury is to our sun. It’s no surprise that the planet, Gliese 436 b, has an incredibly hot surface temperature of 439 degrees Celsius, but it’s definitely a surprise that the planet is also covered in ice. Since the boiling point of water is 100 degrees Celsuis, it seems impossible for ice to exist, but Gliese 436 b’s ice isn’t exactly conventional ice as we know it on Earth. It’s a phenomenon called “hot ice”, or “ice ten”—a kind of hot, solid water. It looks a lot like our ice, but if you touched it, it would pretty much melt through your flesh. It’s not kept in a solid state by a low temperature; instead, the planet’s gravity is so powerful that it pulls all its water vapour towards the core, forcing it together into a densely-packed, solid, hot layer. Even the incredibly hot temperatures can’t evaporate or melt it. Since the ice alone isn’t enough to account for the planet’s estimated radius, it’s thought that on top is an outer layer made up of hydrogen and helium. It’s puzzling, though, because planets with hot, hydrogren-dominated atmospheres are predicted to have significant amounts of methane and no carbon monoxide—but on Gliese 436b, it’s the other way around, and we have no idea why yet.
(Image Credit: 1, 2)