Features

• The Red Planet's Watery Past

  New observations by rovers and orbiters indicate that liquid water not only existed on Mars, it once covered large parts of the planet's surface, perhaps for more than a billion years

  Jim Bell   | December 1, 2006  | 1

• Set Theory

  Patrick Merrell   | December 1, 2006  |

• Cancer Clues from Pet Dogs

  Studies of pet dogs with cancer can offer unique help in the fight against human malignancies while also improving care for man's best friend

  David J. Waters and Kathleen Wildasin   | December 1, 2006  | 1

• Scientific American 50

  The Editors   | December 1, 2006  |

• Lucy's Baby

  An extraordinary new human fossil renews debate over the evolution of upright walking

  Kate Wong   | December 1, 2006  |

• The Ultimate White Light

  "Supercontinuum" laser light has enabled the most precise frequency and time measurements ever and might drive optical data transmission rates to record speeds

  Robert R. Alfano   | December 1, 2006  |

• Weighty Matters

  The century-old artifact that defines the kilogram, the fundamental unit of mass, is to be replaced by a more accurate standard based on an invariant property of nature

  Ian Robinson   | December 1, 2006  |

• Seeking the Neural Code

  Learning how rats escape from cats also reveals how a storm of electrical pulses sweeping across the brain is translated into information

  Miguel A. L. Nicolelis and Sidarta Ribeiro   | December 1, 2006  | 2