A planet battered by ion storms where an Illyrian colony vanished, and where an Enterprise landing party picks up a strange contagion in the Strange New Worlds episode Ghosts of Illyria.
Hetemit IX is the site of a deserted Illyrian settlement investigated by the Enterprise in Ghosts of Illyria, set in 2259. Illyrians modify their own genes, which is why the Federation keeps them at arm's length.
A fierce ion storm cuts the survey short. Most of the party beam up, carrying with them an infection that spreads through light and drives its victims to seek brighter and brighter sources. Pike and Spock are stranded below and take cover in the colony's library, where glowing figures appear in the storm.
Spock learns from the records that the colonists had tried to undo their modifications in the hope of joining the Federation, which left them open to the disease. The beings in the storm are what they became, and they shield the two officers. On the ship, the crisis forces Una Chin-Riley to reveal that she is Illyrian.