An engaging, sporadically informative scan of Mars with coordinates locked in on the 1971-72 voyage of Mariner 9, by an ebullient panel consisting of an optimistic Bradbury, a cautious Clarke and their opposite academic numbers, Carl Sagan (Cornell) and Bruce Murray (Cal Tech) plus New York Times Science Editor Walter Sullivan as interlocutor before a California audience. Initially, Bradbury offers sentiment, wit and amusing asides (he hoped for Martians ""waving signs which read BRADBURY WAS RIGHT"") plus poetic transport (""I sing the entire man -- going into space""); the others gently speculate and supply tributes to fanciful/scrupulous astronomic forerunners. The second section is a collection of 1972 afterthoughts on the material transmitted from Mariner, and all the participants reflect Clarke's contention that its findings are more exciting than their previous guesses. Murray suggests that Mars is in a period of transition, from moon-like to earth-like. Sagan discusses the effects of winds and atmospheric pressure and the possibility of sophisticated microorganisms. Sullivan looks toward new procedures and new planets and Bradbury adds the appropriate music-of-the-spheres coda: ""Follow me./ I know a tune./ Listen."" Fifty Mars photos will be an important feature.