Search for other life intensifies

Venus and three of Jupiter's moons are receiving a lot of attention.
KNIGHT RIDDER NEWSPAPERS
MOUNTAIN VIEW, Calif. -- Encouraged by evidence that liquid water once flowed on the surface of Mars, scientists are stepping up their search for past or present life beyond the confines of Earth.
They're finding water and molecules of hydrogen, oxygen and carbon -- the building blocks of living organisms -- scattered throughout the universe on planets, moons, asteroids, comets and even in the space between the stars.
"The field is energized by excitement and controversy," said Bruce Runnegar, director of the NASA Astrobiology Institute, a collaboration of a dozen universities and research centers studying the origin, evolution, distribution and future of life.
The astronomers, biologists, chemists, geologists and other scientists who make up the astrobiology community think it's highly unlikely they'll find intelligent beings, such as E.T., living on other worlds. If life is found, they say, it most likely will be microscopic, such as the single-celled creatures that ruled Earth for its first 2 billion years.
Exploration
While most of the attention is focused on Mars, NASA is planning an unmanned mission to explore three of Jupiter's ice-covered moons -- Europa, Callisto and Ganymede -- in the next decade. Researchers think microbes might dwell in subsurface oceans in the shadow of mighty Jupiter.
"Life may be quite possible on Europa, but we're not going to know unless we go there," Jere Lipps, a biologist at the University of California, Berkeley, told an astrobiology conference at NASA's Ames Research Center here.
"Life on icy worlds occurs in the solar system and probably throughout the universe," said Lipps, who has dived below the Antarctic ice shelf to photograph a thriving ecosystem. On Earth, he noted, "ice is infested with all kinds of organisms. Life has no problem with ice."
Life on Venus
At the other end of the temperature scale, tiny organisms might be comfortable in the steamy, sulfurous clouds of Venus, some scientists think. In an intriguing parallel, they note that living bacteria have been found floating miles up in Earth's atmosphere.
"Bacteria in cloud droplets at high altitudes on Earth are actively growing and reproducing," said Dirk Schulze-Makuch, a geologist at the University of Texas, El Paso. "Life could exist today in the clouds of Venus."
Europe and Japan are planning to send spaceships to Venus, Earth's closest planetary neighbor, to look for signs of life. The National Academy of Sciences has recommended an American mission as well.
"Venus is more similar to Earth than Mars is," said David Grinspoon, a space scientist at the Southwestern Research Institute in Boulder, Colo. "Many extra-solar planets will probably be like Venus. ... We should explore Venus right next door."
To aid in the hunt for extraterrestrial life, scientists are looking at the ways organisms cope with extreme environments on Earth. They've found microbes living happily in acid, in desert sands, in rocks below the sea floor, even in nuclear waste. One recently discovered species can cope with temperatures as high as 250 degrees, well above the boiling point of water.
These heat-loving creatures dwell in a "witches' kitchen ... a new continent of life," Harald Huber, a microbiologist at the University of Regensberg, Germany, told the conference.
Huber described a newly discovered family of microbes called Nanoarchaea, 100 times smaller than E. coli, the familiar stomach bug, and close to the lower size limit for a living cell.
"This is a good candidate for extraterrestrial life," he said. "E.T. might look like this little guy."