Not too big, not too little.
Goldilocks is a temperate world named by the terran refugee Jake. Due to its location away from the colonized planets of the sector, it was sought as a haven by protoss acolytes to experiment on zerg bioforms. It is a planet of extremes when in terms of its biology and geology, but very hospitable for life.
Goldilocks was named due to it being "just right" in terms of its situation as a planet: nearby a yellow star, three small moons, just large enough to generate tidal forces and keep the planet steady on its axis, 90.09% standard gravity, 73% water covered, 31% oxygen in the atmosphere, and a mean temperature of 24 degrees Celsius. Due to its lower gravity, geologic formations on the planet were more extreme, as mountains and dunes would be much higher and have almost sheer cliff faces. The planet is also known for superstorms, which would come and pass quickly.
The wildlife on the planet is larger due to the higher oxygen content, with the ideal size for an organism being around the size of a football. Jake speculated during his stay there that the more extreme outliers could be around the size of a football field. Plantlife grows very quickly on Goldilocks, with creeper vines being able to cover a structure in a matter of a few weeks.
Goldilocks, due to its location near the borders of the sector, was largely unexplored by the three major races and was left unaffected by the conflicts between them. After the Great War, a group of protoss acolytes moved to a volcano on the world after a dark templar named Lassatar found a xel'naga artifact called the psionic lens. Their goal was to use this artifact to impart individuality on the zerg specimens they brought, evolving them into something that could not threaten the protoss. This backfired, and the zerg overran and killed the acolytes. Lassatar came to the planet on the trail of the lens to discover their fate.
Meanwhile, a Terran Dominion deserter named Jake came to the planet in search of a haven away from the war. He landed on the same volcano, and set up a base camp. After having to take refuge in one of the volcanic caves after a superstorm, Jake found the remains of the protoss acolytes, and ran into Lassatar. However, he later also ran into the zerg, and fought his way out of the cave. Lassatar used the psychic lens to influence Jake into using his colony supplies to destroy the volcano, killing the mutated zerg inside. The volcano erupted, and the zerg were all slain. Both Lassatar and Jake left the world.