Peter Ward's latest offering, "Life as We Do Not Know It: The NASA Search for (and Synthesis of) Alien Life" aims to unravel science's...

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Peter Ward’s latest offering, “Life as We Do Not Know It: The NASA Search for (and Synthesis of) Alien Life” (Viking, 288 pp., $25.95), aims to unravel science’s most profound questions: What is life, and where does it exist?

Despite its weighty subject matter and some original scientific proposals, this challenging volume is eminently readable. Ward is the author or co-author of several previous books, including (with Donald Brownlee) “Rare Earth” and “The Life and Death of Planet Earth, ” and his comfortable style delivers ample doses of personal warmth and humor along with a wealth of information and dazzling speculation.

As a leader in the growing field of astrobiology, which investigates processes on other worlds that could lead to or result from Earthlike life, Ward, a professor at the University of Washington, draws on the work of colleagues in the 15 research institutions that operate worldwide under the umbrella of the NASA Astrobiology Institute.

The book is a fascinating guided tour that begins in the varied environments and laboratories of our own planet (including some where researchers are creating synthetic life) and then proceeds to the most likely and a few unlikely bodies of the solar system where evidence of past or present life may be found.

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Peter Ward will read from “Life as We Do Not Know It,” 7 p.m. Tuesday, University Book Store, 4326 University Way N.E.; free (206-634-3400 or

Over the past 30 years, scientists have discovered microbes that flourish in Earth’s hottest, coldest and harshest conditions. These “extremophiles” prove that life arises and thrives in a much broader range of environments than people once thought possible — not unlike those on Mars or elsewhere in the solar system.

Conditions on Earth favor DNA and carbon-based life, but astrobiologists know that there are non-Earthlike variations of the DNA scheme. They also envision life founded on different chemistries, such as silicon-based molecules called silanes, which might flourish in unearthly realms.

Approximately half of the book is devoted to examining how and where such life might arise today or have arisen earlier in the history of the solar system.

Ward leaves no solar-system world unvisited, though he quickly dismisses most of them. He allots a number of pages to the possibility of life floating high in the sulfuric-acid-laced clouds of Venus. But as expected, Mars gets the most attention outside of Earth.

The Red Planet may have once had a climate suitable for the evolution of simple multi-cellular carbon-based life. Today, bacterial life beneath its surface is conceivable, and ancient Martian bacterial life would certainly have left its signature in the rocks.

Scientists’ favorite place to look for current life beyond Earth is beneath the ice covering a global ocean on Jupiter’s moon Europa. Ward argues that a better bet would be Saturn’s largest satellite, Titan, with its thick atmosphere and hydrocarbon lakes.

In perhaps the book’s most vivid section, he describes an astronaut’s imagined view of one of Titan’s craters: “a phantasmagoric wonderland of hydrocarbon fluid, ice, sludge, and rock, all arrayed in frozen glory … Steaming geysers of methane venting from the warmer interior instantly freeze and then fall as black organic snow … ” That rich and dynamic environment might be just what life needs.

Astrobiologists like Ward imagine carbon-based Titan life with either ammonia or water as its vital solvent. The moon’s extreme conditions might even favor silicon-based life. He proposes sending a biochemist there to find out.

Though such a trip is certainly not on NASA’s immediate agenda, Ward’s suggestion makes sense for the long term. Before that, astronauts will return to the Earth’s moon and then head for Mars. Both missions will seek signs of life’s beginnings. Geologists on the moon will collect ancient pieces of Earth and other planets, transported there by asteroid bombardment during the earliest epoch of the solar system’s history.

Ward’s choice for the first scientist on Mars would be a paleontologist who could dig up a few fossils. By the time readers finish this captivating book, they will have no doubt that he wishes he were young enough to sign up for the job.

Several of physicist Fred Bortz’s previous and upcoming books for young readers ( discuss past discoveries and the future of astrobiology.