This is the second planet in orbit around the star. It is a large gas giant, home to a few simple extreme r-strategists. Life has been here for longer than it's life-bearing moon Iris, and although mutation rates are high, life remains uncomplicated and unicellular.
The planet is composed of water, hydrogen and hydrogen compounds.
Cappu has a number of satellites, most no more than a few hundred kilometers in diameter, and around 5 that are over 1000km diameter, including Iris just over a third of Earth's size.