Rhine is the largest non-stellar body in the Rigel system. It is a gas giant with a blue coloration, composed mostly of hydrogen and ammonia. It is also the primary source of energy in the system, whether it be helium-3, hydrogen, or methane harvesting and refining. Rhine is a parent to just over a hundred moon and planets.

The planet's powerful magnetic field has protected Rigel Prime since capturing it, keeping it safe from Rigel Alpha's deadly ionizing radiation. As a result, the planet itself is popular in Rigellian fiction and literature, and is the focus of the Star Kingdom of Rigel's extensive Rhine Development Edict which strictly limits contamination and overharvesting. The measure is considered a formality due to Rhine's effectively unlimited resources.

Like the other gas giants in the Rigel system, it is named for a famous Terran river.