Your ship’s temperature is influenced by the surrounding environment. For instance, when you're near a star, it emits heat. The closer you get to the star, the more your ship’s temperature rises. On the other hand, moving farther away from the star causes your ship’s temperature to gradually drop.
Keep a close watch on the Heat Bar to prevent overheating. Should your ship overheat, you will be unable to operate your interstellar jump drive, meaning you will be unable to leave the system via the jump drive.