Class Y planets are planets found in all zones of the solar system, from cold to hot. They are planets with a solid surface, but temperatures on its surface are around 500 K. Their atmosphere is mostly toxic, and these planets are often full of thermionic radiation. Due to their hostile environment, they are nicknamed the "Planet Demon". They are completely unsuitable for any humanoid life, even entering their atmosphere is considered a great risk, on their surface most materials do not last long and begin to corrode quickly. Although unsuitable for humanoid life, intelligent mimetic matter has been discovered on one of these planets in the Delta Quadrant, mimicking the living forms (and more) they have encountered.