On the Cover: Life, as we know it, is a chemical process. The elements that make up living things were created deep within giant stars. In the stars' death throes, these elements are released to space, where they can combine into the dark molecular clouds strung among the stars (seen here as dark streaks in the Trifid Nebula). On Earth, we find wonderfully diverse manifestations of living chemistry (clockwise from top left): densely crowded coral reefs; rich, extravagant rain forests; and intelligent, language-using dolphins. We also find a species that has questioned how life began and is now using its technology to search for answers among the planets and stars. Clockwise from top leff, Carl Roessler, Brian Parker and Ed Robinson: Tom Slack and Associates; JPL/NASA; background, National Optical Astronomy Observatories
3 Life in the Universe: Donald DeVincenzi introduces our special issues looking at the most fundamental questions about life.
6 Chemstry Between the Stars: William Irvineexplains how biogenic elements—formed deep within stars—traveled across space to make up life on our planet.
10 The Origin of Life: James Ferrisdiscusses the chemical processes of life.
12 Mars, Then and Now: Norman Horowitztakes us on a historical tour of our view of the Red Planet.
14 Biology and the Exploration of Mars: Harold Klein reports on our current state of knowledge about Mars, and the possibility of past or present life there.
16 Time Travel and Chemical Evolution: A Look at the Outer Solar System: Tobias Owen tours the chemical environments of Jupiter and beyond, and their potential for life.
20 Finding and Studying Other Planetary Systems: David Black looks at the prospects for detecting extrasolar planets—and with them, extraterrestrial life.
23 The Windows of SETI—Frequency and Time Travel in the Search for Extraterrestrial Intelligence: Bernard Oliver thinks that if we do not begin our search soon, we'll lose the opportunity to do so from Earth.
26 Terraforming: Making an Earth of Mars: Christopher McKay goes over some of the possibilities for creating an Earthlike environment on our nearby neighbor.