In 2267, Appel served as an engineer at the underground pergium mining colony on Janus VI. Appel was one of the first to encounter the Horta, a "monster" that could burrow through solid rock, and was destroying machinery and killing the miners. Upon his encounter, Appel used a hand phaser and injured the creature.

When it was learned that the Horta was an intelligent lifeform, and a mother protecting her eggs, Appel and the other miners reached a peaceful alliance with the creature.