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