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THE SILENT EARTHQUAKE MENACE • A SCIENCE OF FAIR VOTING The Time Bomb of Global Warming (and How to Defuse It) MARCH 2004 WWW.SCIAM.COM $4.95 Robots on Two Worlds On MARS, twin rovers explore baffling landscapes On EARTH, robotic vehicles race across the Mojave Desert How Addiction Reshapes Brains Flu Vaccines’ Biotech Future (see page 16) COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. contents march 2004 SCIENTIFIC AMERICAN Volume 290 Number 3 features PLANETARY SCIENCE 52 The Spirit of Exploration BY GEORGE MUSSER NASA’s robot rover scouts unknown terrain on the Angry Red Planet. INFORMATION TECHNOLOGY 58 A New Race of Robots BY W. WAYT GIBBS This month a grueling off-road race through the Mojave Desert may crown the most capable robotic vehicles ever. But for the engineers behind the machines, the race started long ago. CLIMATOLOGY 68 Defusing the Global Warming Time Bomb BY JAMES HANSEN Troubling geologic evidence verifies that human activities are shifting the climate. But practical actions to clean up the atmosphere could slow the process. 52 Mars yields BIOTECHNOLOGY grudgingly to robot probes 78 The Addicted Brain BY ERIC J. NESTLER AND ROBERT C. MALENKA Better understanding of how drug abuse produces long-term changes in the brain’s reward circuitry opens up new possibilities for treating addictions. EARTH SCIENCE 86 The Threat of Silent Earthquakes BY PETER CERVELLI Not all earthquakes cause a noticeable rumbling. Recognizing the quiet types could be a tip-off to imminent devastating tsunamis and ground-shaking shocks. ELECTORAL SYSTEMS 92 The Fairest Vote of All BY PARTHA DASGUPTA AND ERIC MASKIN Surprisingly, in elections best designed to read voters’ wishes, the winner should not always be the candidate w