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A 400-YEAR-OLD HOAX? • $1-MILLION PROOF FOR THE SHAPE OF SPACE JULY 2004 WWW.SCIAM.COM Mad Cow Disease: Faster Tests, Future Therapies When Methane Ruled Climate Nanosensors Based on Magnetic Effect COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. contents july 2004 SCIENTIFIC AMERICAN Volume 291 Number 1 features ASTRONOMY 50 The Extraordinary Deaths of Ordinary Stars BY BRUCE BALICK AND ADAM FRANK In five billion years, our dying sun will unfurl into one of the firmament’s premier works of art: a planetary nebula. GENETIC ENGINEERING 62 Gene Doping BY H. LEE SWEENEY Gene therapy for restoring muscle lost to age or disease is poised to enter the clinic, but elite athletes are eyeing it to enhance performance. INFORMATION TECHNOLOGY 70 Magnetic Field Nanosensors BY STUART A. SOLIN 50 Cat’s Eye nebula The recently discovered effect called extraordinary magnetoresistance could enable future computer disk drives to have massive capacities and be blazingly fast. ATMOSPHERIC SCIENCE 78 When Methane Made Climate BY JAMES F. KASTING Today methane-producing microbes are confined to oxygen-free settings, such as the guts of cows, but in Earth’s distant past, they ruled the world. BIOTECHNOLOGY 86 Detecting Mad Cow Disease BY STANLEY B. PRUSINER New tests can rapidly identify the presence of dangerous prions—the agents responsible for the malady. Several compounds also offer hope for eventual treatment. MATHEMATICS 94 The Shapes of Space BY GRAHAM P. COLLINS A proof of the century-old Poincaré conjecture helps mathematicians understand three-dimensional space. CRYPTOGRAPHY 104 The Mystery of the Voynich Manuscript BY GORDON RUGG Cryptographic analysis of a fa