Tyrellia is a planet of ice located in the Karideph system. Lying slightly outside of the habitable zone around the system's sun, the planet is a very cold one. However, this does not stop people from living there, since the atmosphere is breathable. In fact, there are several 'health clinics' on the planet that insist that the sharp, cold air is perfect for treating almost any ailment, even though there have been no credible studies to support this. However, lack of proof does not stop thousands from flocking to the planet to administer the "frost" treatment.
There have been several asteroid impacts on the surface of the planet, which a few areas that are not covered by ice can attest to. It has been suggested that there was a major asteroid hit early in the planet's history that may have knocked it out of the reach of the system's habitable zone. This would explain the large sea of lava, and volcanoes that reside within the southern half of the planet, because only a huge impact could have penetrated the surface of the planet and reveal the lava below while the subsequent destabilization of the surface around the impact area would allow magma to surface, creating volcanoes. There is a constant battle between the cold of the atmosphere and the heat of the lava that makes the ice and ground around the lava sea very unpredictable.
As further proof for the scientists that the asteroid hit knocked it slightly out of orbit, there is a swath of forest just to the east of the lava. Slightly protected from the cold by the crevasse in which it lies, along with the heat from the lava, it has remained there for thousands of years. Tests have shown that the trees themselves are older than the rock surrounding the lava sea, indicating that they were alive before the impact. This implies that the planet's surface was much warmer than it is now. Many rare and wonderful creatures live there, but few expeditions to the forests ever come out again. This has caused the myth of an all-powerful guardian spirit that protects the forest to spring up amongst the colonists, who have refused all requests to harvest or develop within the forest. It is yet to be determined what will happen when the developers finally get their hands on this prime real estate.