The hunt for life out in the universe is on.
Spurred by evidence of primitive life discovered last month in a Martian asteroid, scientists from America's major space research centers gathered here this week to plot the next steps in the search for extraterrestrial life.
The discussion at the three-day meeting ranged from the search for planets around other stars to examining the complex chemistry that created organic life on this planet several billion years ago. The conference marked the launch of a new field of research - astrobiology - which unites a wide range of scientists, including astronomers, physicists, chemists, and biologists in an unusual interdisciplinary study of the origin and evolution of life in the universe.
The workshop was designed to examine five key questions:
* How does life originate?
* Where and how are other habitable worlds formed?
* How have Earth and its biosphere influenced each other over time?
* Can terrestrial life be sustained beyond our planet?
* How can we put humans on Mars?
The excitement behind this effort comes from more than the signs of a Martian microbe. In the last year, astronomers have detected eight planets in orbit around stars distant from our own solar system - discovery of a ninth planet was also revealed here. And evolutionary geneticists have determined the genetic structure of a third, primitive form of life - known as the Archaea - which exists even now under very extreme conditions on Earth.
The researchers believe this provides growing evidence of the possibility of a life evolving on other planets, under circumstances more hostile than previously thought possible. Life could exist in several different places within our own solar system, including Titan, a moon of Saturn, and Europa, a moon of Jupiter covered with a sheet of ice underneath which is believed to be water, argues astronomer Carl Pilcher, from NASA's Office of Space Research.
But at the center of attention is the Red Planet itself, long believed the best hope for finding evidence of life outside our own Earth.
"The question of whether Mars had independent life, either in the past or in the present, is one of the most important questions in science," says David Morrison, director of space at NASA-Ames Research Center, the host of the conference and the center of planning for this search.
The failure of the Viking landers in 1977 to discover signs of life on Mars discouraged many scientists. But the Martian meteorite has reinvigorated this venture. The single sample, discovered in Antarctica, contains tantalizing evidence of fossilized bacteria about 3.5 billion years old, along with organic chemical and carbonates that accompanied the emergence of life on Earth. The findings, though still not conclusive, suggest that there might have been sustained creation of life forms about the same time scientists have dated it happening on Earth.
Still the Mars rock "is not going to give us an answer the scientific community can converge on," says Christopher McKay, an Ames scientist who has been involved in this research since 1980. Discovery of a second meteorite is unlikely, he says. "We may actually have to break down and go to Mars to get our second rock."
NASA is planning to send a dozen spacecraft to Mars, starting with two this year (and collaboration on a third, Russian spacecraft), including sophisticated surface robots that can collect samples and return them to Earth.
Scientists generally agree that the key to life is liquid water, which based on the geological evidence of dried rivers and lakes, existed at one time on Mars's surface. "The period when life formed on Earth is the same period when water is on Mars," Dr. McKay told the meeting. "This drives the notion that Mars might have had life."
Mars's thin atmosphere and extreme cold now allows only for ice and frost, but McKay and others believe it is possible there may be water under the surface, and with it, some forms of life. At the least, the evidence of life in ancient Mars will help scientists understand the evolution of life on Earth.
ULTIMATELY a manned flight to Mars offers the best chance to investigate this great mystery. Astronaut Scott Parazynski discussed some of the challenges involved, among them long durations of microgravity, the risk of solar radiation, and the psychological stresses. Advanced propulsion technologies could cut a flight of hundreds of days to 90 days each way, he says. "Travel to Mars is almost within the grasp of current technology," says Dr. Parazynski, a veteran with 262 hours in space.
Beyond Mars, there is the search for life in other solar systems. James Kasting from Pennsylvania State University maintained that planets capable of sustaining life must lie within a "habitable zone." The zone, determined by a star's brightness and the planet's distance from it, is defined as the range that permits the existence of liquid water.
Some nine planets have been discovered recently by a team of scientists based at San Francisco State University, but all of them lie outside this zone. Geoffrey Marcy, a leader of this team, described expanded efforts to discover new planets based on ground-based observations. But he urged backing for sending instruments such as spectrometers, which scientists use to break down starlight to determine its chemical composition and even its relative motion, into space. Other proposals for detecting new planets and analyzing their atmospheres for possible evidence of life were aired, including Ames astronomer David Koch, who has designed a low-cost satellite system to monitor 140,000 stars to try to detect Earth-sized planets.
All these plans require new funding at a time when NASA faces a steadily declining budget. But NASA scientists are hopeful that the excitement surrounding the Mars rock discovery will open the door to new backing. Hearings on the Mars work are scheduled to be held this week in Congress.