Star Trek: Voyager: Season 4, Episode 24

4 - 24: Demon

Stardate: Unknown - In search of the vital chemical deuterium essential to Voyager's energy supplies, they discover a hostile "Demon class" planet with reserves large enough to replenish the ship. Ensign Kim and Tom Paris take a shuttlecraft to the planet's surface in environmental suits. Soon they are found on the planet without suits, and the ship's atmosphere becomes poisonous to them.