Pro Eur XI-X c28-20 houses four T-Tauri stars, and compared to many other such systems, this system has an unusually valuable assortment of planets. Around the secondary stars, there's one Earth-like World and four Water Worlds, one of which is a candidate for terraforming. In addition, there's another terraforming candidate, a High Metal Content planet.

This is made possible by having the three secondary stars (B, C, D) orbiting each other quite closely, and the string of valuable planets co-orbits these three. As such, the three T-Tauri stars combined are enough to keep the Water Worlds heated - although in the cases of the outermost two (BCD 5 and 6), the greenhouse effect of having a (mostly) carbon dioxide atmosphere contributes a lot to this.