WASHINGTON - If liquid water is present on Mars, as suggested by a new study, then all elements are in place for the possible presence of life on the Red Planet, experts said Thursday.
A new study, using high resolution photographs from the Mars Global Surveyor spacecraft, has spotted gullies and trenches and fanlike deltas that could have been carved by fast-moving water flowing down cliffs and the steep walls of craters.
Experts said that the possibility of liquid water on Mars is a controversial theory, but that if it is true then it greatly increases the likelihood for life on Mars.
That liquid water once existed on Mars is generally accepted by scientists, but Michael Malin said his new study suggests strongly that water flowed on the Red Planet very recently and, perhaps, even now. He bases this on photos showing gullies and rills the look very much like similar water-carved features on Earth.
''The features appear to be so young that they might be forming today,'' Malin said at a news conference on Thursday. ''We think we are seeing evidence of a ground water supply, similar to an aquifer.''
''Finding possible evidence for liquid water has profound implications ... for the possibility of life on Mars,'' said Ed Weiler, chief scientist for NASA, the agency that built and launched the Surveyor spacecraft.
''If you think about the requirements on Mars to support life ... the key comes down to liquid water,'' said Bruce Jakosky, a professor at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder.
''On Earth,'' said Jakosky, ''wherever you find liquid water below the boiling temperature, then you find life.
''This doesn't tell us that life does exist on Mars, but it is the smoking gun that tells us Mars has all of the elements for life,'' he said.
Malin and Ken Edgett, both with Malin Space Science Systems of San Diego, notified NASA a month ago that they had spotted in Surveyor photos evidence that water has flowed very recently on the surface of Mars. They are co-authors of study to be published next week in the journal Science and the principal scientists analyzing photos from the Surveyor.
NASA held a news conference Thursday to announce the findings. Science, a leading peer-reviewed journal, advanced by a week the embargo on the study and will publish it next week.
Malin said that he and Edgett found evidence for the flow of liquid water in 200 of 65,000 photos taken by the Surveyor's high resolution camera.
They concluded the water action was recent because surfaces around the carved gullies are smooth. Older surfaces on Mars are pocked with craters and covered with a dark dust, they said.
''That tells you something is happening right now, or within a year or two,'' said Edgett. ''These are very, very young.''
Both Edgett and Malin said they were very reluctant at first to believe that water has flowed recently on Mars, but that the evidence eventually prompted them to pose the theory.
Michael Carr, a geologist and Mars expert with the U.S. Geological Survey in Menlo Park, Calif., said the Surveyor images ''are quite compelling'' and the interpretation that recent water flows carved the face of Mars ''is very, very plausible.''
However, Carr said Mars is very cold - minus 97 to minus 148 degrees F - and it is hard to explain how water could flow without freezing.
''It is important to be cautious about the interpretation (by Edgett and Malin),'' said Carr.
Edgett said that most of the places that appear to be the source of flowing water on Mars are on slopes with exposed rock layers. He said it is possible that liquid water is trapped below the rock layer and is then freed by a surface shift.
He said one possible explanation is that water would freeze and form an ice dam as it flows from an underground source. The ice dam would retard the flow until there is enough force to break through the dam. The water would then cascade rapidly down the slope, rather like a flash flood. It would quickly freeze as its motion slows, providing, perhaps, an explanation for the light-colored, frosty-like appearance of some patches of ground near the water courses.
Previous studies have detected land features on Mars carved by water, but it is thought that this happened billions of years ago. It is thought that Mars once had oceans and rivers, and a warm, thick atmosphere. Over time, Mars lost its atmosphere and became very cold. The atmospheric pressure now is so low that liquid water converts directly into a vapor, and it is thought that much of Mars' water has escaped into space in that form, leaving behind ice caps at the poles.
Weiler said that if the presence of subsurface liquid water can be proven on Mars, it will quicken the possibility of sending humans to Mars.
''These data are compelling,'' he said. ''If we ever had the desire to send humans to Mars, that desire should be even stronger now.''
But before such a mission could be mounted, Weiler said NASA needs to conduct decades of robot studies of the Red Planet. Currently, the agency plans to send new missions to Mars every 26 months. Much of the effort will be directed toward reconnaissance, finding interesting and likely places to land robots and, perhaps eventually, human beings, he said.
Experts also have said that readily available water would make it easier to colonize the Red Planet. Water can be broken into its chemical parts, hydrogen and oxygen, which can be used as rocket fuel. Oxygen split from water also could used as a breathable atmosphere inside a Martian base.
On the Net: Mars Global Surveyor site: http://www.marsnews.com