Planet of the Gods by Harry Leon Wilson, Science Fiction, Adventure, Fantasy (Paperback)

"What do you make of it?" Commander Jed Hargraves asked huskily.

Ron Val, busy at the telescope, was too excited to look up from the eye-piece. "There are at least two planets circling Vega " he said quickly. "There may be other planets farther out, but I can see two plainly. And Jed, the nearest planet, the one we are approaching, has an atmosphere. The telescope reveals a blur that could only be caused by an atmosphere. And--Jed, this may seem so impossible you won't believe it--but I can see several large spots on the surface that are almost certainly lakes. They are not big enough to be called oceans or seas. But I am almost positive they are lakes "

According to the preconceptions of astronomers, formed before they had a chance to go see for themselves, solar systems were supposed to be rare birds. Not every sun had a chance to give birth to planets. Not one sun in a thousand, maybe not one in a million; maybe, with the exception of Sol, not another one in the whole universe.

And here the first sun approached by the Third Interstellar Expedition was circled by planets

The sight was enough to drive an astronomer insane.