Gliese 436 B is my new favourite planet. Not because of it’s catchy name, but because of one of the most unusual properties found anywhere in our solar system. Gliese 436 B is a Neptune sized ice world, yet orbits its star at a very toasty 4.3 million miles. That’s almost fifteen times closer to its star than Mercury is to the sun. And yet 436 B stays completely frozen. It is literally an ice cube on fire. The surface on Gliese 436 B stays at a constant temperature because it is so close to its star, and that temperature is a whopping 439 °C. Given that water boils at 100 °C, the presence of ice should be an impossibility. Except its not really ice, at least not in the classical sense. It’s a phenomenon knows as hot ice or ice-ten. It would look much like the ice we have here on Earth, but if you were to and pick some up, you would need a new hand.
The vast amounts of water that make up the planet are kept in a solid state by gravity pulling the water molecules towards the planets core. This means that even the searing surface temperatures aren’t enough to evaporate the water away from the planet, instead the water molecules are kept densely packed together pulled towards the core. Gliese 436 B probably started out life as a gas giant, similar to Jupiter, orbiting a star much like our sun. That star has since entered its final stage and has exploded in size to become a Red Giant. Red Giants are much cooler than main sequence stars, with a surface temperature of around 4,500 °C. The sun will become a red giant in an estimated 5 billion years time, possibly destroying the Earth in the process. It seems Gliese 436 B wasn’t destroyed by this event as it was far enough away, but has had it’s entire atmosphere burned off leaving just a tiny ice cube floating around a dying star. Once every two and half days. On fire.