Char was formerly one of the thirteen core worlds of the Confederacy, but it is most notorious as the primary hive planet of the alien zerg. Upon its discovery, Char was found to be an inhospitable volcanic planet with thick ash covering most of its surface and tainting its acrid atmosphere. The hazardous environment is further intensified by extremely high levels of cosmic radiation from Char’s volatile pairing of binary stars, a class VI F0 sub dwarf orbiting an M8 irregular variable. Char’s elliptical orbit means whole regions of its sunward face can become molten seas during a close approach, with temporary islands forming in them due to rapid cooling as the planet swings away to the frozen outer reaches of the system.
You can find more information of this planet directly from the starcraft2 website.
Source:
Starcraft2.com