Gliese 436 b is currently one (if not the top)v of the strangest, most inexplicable exoplanets we’ve currently found. It’s a Neptune-sized planet that orbits a red-dwarf star (Gliese 436) approximately 33.1 light-years away in the zodiac constellation of Leo.
The exoplanet, which is similar in size to Neptune, makes a full orbit around its parent star in just 2 days and 15.5 hours, making it about 13 times closer to its parent star than Mercury is to the Sun. Because of this close proximity, the planet’s surface temperature is estimated to be around 712 K, which is significantly higher than one might expect if the planet were only being headed by radiation. The explanation astronomers have came up with is that the temperature has peaked to this level due to a runaway greenhouse gas effect similar to the one experienced on Venus.
Perhaps what sets this planet apart from all of the other exoplanets we’ve discovered is that despite being so close to its parent star, the planet is layered in burning ice! How is that even possible?! Astronomers believe the exoplanet has a core consisting of large quantities of ice, with water vapor in its atmosphere. It probably originated in the outer solar system before migrating inwards towards its parent star. During this process, much of the planet’s hydrogen envelope would have been blown away via coronal mass ejection from its parent star. The gravity on the planet is so substantial, it has been able to compress the remainder of the water vapor found in the atmosphere into an exotic phase of water that can be heated up exponential whilst remaining in a solid state. We now call Ice X, though similar in name to the frozen water used to cool off a warm beverage, it’s nothing at all like it. For catching a drop of it in your mouth would require you to get a new mouth.
Another puzzling aspect of this exoplanet is the lack of methane in the planet’s atmosphere. Planets that experience blistering temperatures present in their atmosphere’s hydrogen-dominated atmospheres are expected to contain significant amounts of methane too, with no carbon monoxide. On Gliese 436 b, the opposite is true and we aren’t of the cause yet.