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What will happen to the Huygens probe when it plunges through Titan’s atmosphere? Will we have a PHHT or a BOOM? My late father, a chemist, always admonished me to beware of acetylene, propane, and ethane, as they were highly volatile.

Caroline L.C. Goldsmith
Hackettstown, N.J.

” There is no molecular oxygen on Titan,” responds Jonathan I. Lunine of the University of Arizona in Tucson, “and therefore ethane and propane will not ignite or explode. . . . Acetylene is a bit different—it spontaneously forms a polymer, releasing heat, but explosive polymerization requires oxygen .”—R. Cowen