As for habitability, Planet No. 3 is more suitable for habitation.
Because its distance from the sun is most suitable, and the climate is particularly good, which is very similar to Earth's situation.
However, it is only half the size of Planet No. 1, slightly larger than Planet No. 2.
Moreover, there are no Star Gates present on it.
It's unknown whether there weren't any in the first place, or if they were destroyed by the civilization above. The Spirit Race searched for a long time but found no unique signal of the Star Gate.
Due to this, the Spirit Race did not discover its existence earlier.
Furthermore, its orbit is different from that of Planet No. 1 and Planet No. 2, making it not so easy for them to see each other.
It takes several hundred years to see one another.
Thus, the Spirit Race discovered Planet No. 3 through an exploration spaceship.
Unfortunately, after they sent some spacecraft in, the signals were quickly lost.
