Lunan's book is a superb monument to the state of human knowledge of the Solar System at the end of the 1970s, after the Pioneer probes had returned their data but just before the Voyager encounters with the gas giants. The Moon is described in the light of the Apollo missions' discoveries, Mars after the Vikings, Venus after the Soviet Veneras and American Mariners, and the more distant worlds with the sparse information available (Jupiter and Saturn with Pioneer returns, the outermost three planets in the light of sparse telescopic data, the spaces beyond with theoretical insights). It's interesting to read, in Lunan's engaging prose style, about the issues preoccupying planetary scientists at the time. The possibilities for Jovian life and for massive gas-giant planets beyond Pluto are raised, for instance, while the existence of the Kuiper belt and Venus' peculiar planetological environment are not. Ganymede, curiously, is oput forward as the Galilean moon with the greatest likelihood of an underice planetary ocean, not Europa. Too, it's depressing to realize that, in the absence of any dedicated planetary exploration missions, we know barely more about Mercury and Pluto than we did at the time of Lunan's writing.
What makes New Worlds for Old particularly interesting are the chapters contributed by guest authors. A.E. Roy describes strategies for interplanetary navigation; John Macvey speculates about the potential for life elsewhere in the Solar System; A.F. Nimmo imagines the impending massive colonization of the Moon; A.T. Lawton speculates about what lies in interstellar space. With the exception of Macvey, these authors are concerned with describing the impending colonization of space: Nimmo confidently expects that of the 12 billion humans alive in 2050, 30% would live on the Moon, on Mars, and in O'Neill cylinders. Lawton's essay is of particular note, imagining advanced human civilizations capable of creating stars out of interstellar dust using reverse Bussard ramjet engines. (The failure of this otherwise forward-looking essay to imagine brown dwarves is another interesting lacuna.) Lunan's guest authors are uniformly confident that humanity's future lies offworld, that the great schemes put forward in the 1960s and 1970s in the full flush of the space race will be fulfilled. It would have been nice if these schemes could ever have been fulfilled, but we're left with these essays, memorials to lost dreams.
New Worlds for Old does show its age, but it isn't structurally unsound. As a basic introduction to the Solar System, it still works nicely enough. As a sampling of the unrealistic plans for space colonization mooted decades too early, it's priceless.