Answer: Uranus

One of the interesting characteristics of Uranus’s atmosphere is that it is largely methane gas and it is a much, much, higher pressure than the atmosphere here on Earth. That alone is a novel enough fact, but research conducted in the early 1980s by scientists at Livermore National Laboratory adds a twist to the story.

The scientists, lead by Marvin Ross, hypothesized and then demonstrated with controlled experiments that methane under extreme pressure and temperature will separate into hydrogen, carbon, and–most importantly–create diamonds out of thin air. In other words, the atmosphere is Uranus is essentially a giant methane pressure cooker that continuously rips apart the methane and rains down diamonds upon the planet’s surface.