The Smoke Ring by Larry Niven (1990, Paperback, Reprint)

There is a related book called the Intregal Trees. In the distant future a spacecraft from Earth discovers a strange star system. The is a ring of breatheable atmosphere in a ring between to planets. The is dense enough that their is a whole ecosystems exits. The crew contains "corpsicle" person that were frozen in our time and "revived" by putting all the memories in a body from that time. This stories about people exploring and colonizing that world. It is definately worth a read.