Hanon IV was the inhabited planet in the Hanon system. This world was located near Kazon-Nistrim space in the Delta Quadrant. It appeared to be a M-class planet in the Pliocene stage of evolution, comparable to Earth several million years earlier.
In late 2372, the crew of the USS Voyager were marooned there by First Maje Jal Culluh. Left without any technology, they were forced to live there for days to weeks, with little food and water. While there, they made first contact with the natural humanoid inhabitants. After a volcanic eruption and Commander Chakotay saved one of their kind, their relations improved, initially being one of violence. They were rescued a short time later after Voyager had been retaken, but two crewmembers were killed on the planet. (VOY: "Basics, Part I", "Basics, Part II")
In the late 24th century, Hanon IV suffered a period of severe seismic and volcanic activity. Earthquakes were not rare, and volcanic eruptions were periodic. There were various caverns, some looking almost constructed.
The planet's temperature varied greatly from day to night. During the day, it was often intensely hot, while at night very cold temperatures were common. In the area surveyed, water was not initially found.
Plants with nutritional value were hard to find, but the proto-humanoid inhabitants found some plants, and herbs that could be used for medicinal purposes. Shrubbery existed, and wooden branches could be found lying around. The planet was also home to a species of edible cucumber-like vegetable growing plentifully on vines.
Apart from the humanoid natives, Hanon IV was home to several other known species of animals. These included insects, and small, edible worm-like grubs, that lived under rocks. Large white eggs were also observed.