Pyro IV is the outermost moon ofPyro V, and astronomers theorize that it was once the fourth planet from the sun of the Pyro system. At some point before Humans discovered Pyro, a massive celestial body collided with Pyro IV, catastrophically warping its landscape, destroying its atmosphere, and knocking it into the orbit of nearby gas giant Pyro V. Although the tectonic activity that resulted from this impact has quieted and a new atmosphere has formed, Pyro IV is far from stable. It is on a long, slow collision course with Pyro V, and will one day either crash into it or break up into a ring.