I discovered this extremely rare configuration during the Distant Worlds 3 expedition. An Earth-like planet orbiting as a moon of a Class IV gas giant already unusual on its own. The real surprise is that the Earth-like world has a moon of its own, and that moon is landable. This moon orbits so close to the Earth-like that it appears to be record-worthy: the distance is around 12 Mm (depending on where you land), which is barely 0.04 ls. As an exploration‑focused player with over 3,500 hours in the game, this was a true bucket‑list discovery for me even now I can hardly believe I found it.

The point of interest in this system is the Earth-like world (8 a) orbiting a gas giant, and its own nested moon. Such planets that are satellites of a gas giant are already very rare, and when they have their own nested moon, it's even more rare.

Thankfully, these moons are often landable, and this one is no exception. It doesn't hold an atmosphere. Since nested moons orbit their parent moons at relatively small distances - this one is around 12 Mm away from the Earth-like, or less than 0.04 ls - the parents appear to be enormous, covering a large part of the sky.

While the moon doesn't have an atmosphere, nor life on its surface, it does have volcanic activity. After all, both the Earth-like world and the gas giant exert serious tidal forces on it.

Its parent moon is an Earth-like world that's quite cold, but still habitable. Even then, it only holds an average surface temperature of 265 K thanks to the presence of water vapour in its atmosphere. While 0.23% doesn't sound like a lot, without its contribution via the greenhouse effect, the world would have fallen below 260 K and would no longer be considered habitable.

This system was discovered during the Distant Worlds 3 expedition, in 3312.