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GENETIC CODE: EVOLVED TO EVOLVE • CHOICE AND MISERY SPACESHIPS, INC. The Race to Build a Low-Cost Launch Industry APRIL 2004 WWW.SCIAM.COM Neglected Cells Hold Keys to Thought and Learning The First Nanochips Have Arrived Dusty Clues to Hidden Planets COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. $4.95 april 2004 SCIENTIFIC AMERICAN Volume 290 Number 4 features NEUROSCIENCE 54 The Other Half of the Brain BY R. DOUGLAS FIELDS Glial cells, long viewed as mere support players in the brain, may be nearly as critical to thinking and learning as neurons. PLANETARY SCIENCE 62 The Hidden Members of Planetary Systems BY DAVID R. ARDILA Planets sweep their orbits clean of the dust left in space by comets and colliding asteroids. Those telltale trails can help us spot planetary systems around other stars. PSYCHOLOGY 70 The Tyranny of Choice BY BARRY SCHWARTZ Common sense suggests that having abundant options frees people to find the best route to their own happiness. But in fact, studies show that too much choice often makes for misery. INFORMATION TECHNOLOGY 76 The First Nanochips BY G. DAN HUTCHESON As scientists and engineers continue to push back the limits of chipmaking technology, they have entered into the nanometer realm. 54 Glial cells regulate neurons in the brain BIOTECHNOLOGY 84 Evolution Encoded BY STEPHEN J. FREELAND AND LAURENCE D. HURST New discoveries about the genetic code’s robustness reveal nature’s sophisticated program for protecting life against catastrophic errors while accelerating evolution. SPACEFLIGHT 92 Blastoffs on a Budget BY JOAN C. HORVATH Private ventures seeking to make access to space easy and affordable see a big potential in small vehicl