MARS PROBES TO RENEW SEARCH FOR SUSPECTED MICROBIAL LIFE.

Byline: William J. Broad The New York Times

They have no antennae or pointy little heads or the kind of death rays that H.G. Wells pictured in his "War of the Worlds." Even so, Martians may very well be real and living comfortably in secluded parts of the red planet, scientists are beginning to suspect.

These hidden residents of Mars are envisioned not as large and complex organisms but as tiny specks of life smaller than a pinprick that flourish deep underground in the wet and more temperate regions of the planet's hot interior.

By nature, such a microbial realm would have eluded the pair of robotic probes that landed on Mars two decades ago but found no signs of life on the dry surface. The denizens of the Martian deep, if they exist, may be hard to find and disappointing to some people because they probably resemble the scum around a shower stall more than the freaks of science fiction.

Even so, experts say, the discovery of extraterrestrial microbes would be a watershed in science. Finding life on another planet would shed light on the mystery of how it started on Earth, especially if, as some analysts believe, Martian life evolved earlier. The discovery also would help figure the odds of life arising elsewhere in the universe.

A renewed hunt for life on Mars, especially microbes, is to begin later this year. Driving the exploration are recent findings that early Mars was hotter and wetter than previously believed and that microbes love such environments.

Since the Mars landings two decades ago, microbes on Earth have been found thriving in places, like seabed volcanoes, that are extraordinarily hot, dark, deep and deadly to all other forms of life. Moreover, genetic studies have shown that microbes living in these extreme environments are most closely related to the first forms of terrestrial life, suggesting that evolution began in a hothouse, as Mars might have been some four billion years ago.

"We're in a different world," Michael H. Carr, a scientist with the U.S. Geological Survey who led some of the Mars-probe analyses two decades ago, said in an interview. "Our understanding of biology has advanced so much in the past 20 years. The probability that life could have started on Mars is greatly increased."

Jack D. Farmer, a Mars specialist at the National Aeronautics and Space Administration, echoed that judgment.

"We now know that liquid water was abundant at the beginning and probably still is, below the surface," he said in an interview. "So you have to ask, why not life? What are the chances? I give it 50-50. But that's religion. What we need are more observations."

Later this year, a pair of rockets carrying NASA payloads are to blast off for Mars to inaugurate a potent new round of international exploration. In the next decade or so, America, Europe, Russia and Japan are planning to send as many as 20 missions to Mars, if enough financing materializes. The main goals of the exploratory push are to find water and life.

Even the discovery of fossil microbes or the biochemical forerunners of life would be an extraordinarily precious find, scientists say. On Earth, wind, rain, erosion and geological tumult over billions of years have erased most clues to what things were like in the beginning. Mars is different.

"Much of its surface is ancient and might have a record of what went on in its earliest history," said Michael A. Meyer, head of NASA's program to find extraterrestrial life. "Exploring it might give us a window into the first billion years of our solar system and the origin of life, on Earth as well as Mars."