A decade of studying the data sent back by the American Viking mission to Mars has yielded no recognized sign of life. But Viking's ample evidence of long-vanished lakes and streams makes many planetary scientists wonder what might once have lived there. Studies of frozen-over Antarctic lakes, which teem with microbes and may be similar to ancient ice-capped lakes on Mars, whet their interest. More than ever, planetary scientists see Mars as their prime subject for on-site research -- especially for joint US-USSR projects.
Life in a lake under a dozen feet of ice isn't as fanciful as it may seem. National Aeronautics and Space Administration (NASA) Antarctic researchers have found an abundance of microorganisms in such isolated waters. The lakes are in so-called ``dry valleys'' where there's less precipitation than in the Gobi desert and air temperatures average -20 degrees C (4 degrees F).
Lakes that formed in these valleys 100,000 to 200,000 years ago now lie beneath 10 to 15 feet of ice. This keeps their water well above freezing throughout the year. Temperatures in Lake Vanda, the warmest of seven Antarctic lakes studied, run as high as 25 degrees C (77 degrees F).
In a recent announcement, NASA explained that astrophysicist Christopher McKay and biologist Robert Wharton of the Ames Research Center have found that changes in the ice cap itself help heat the lakes. The ice layer loses about three feet a year through sublimation -- a process in which solid ice turns directly into water vapor without first melting. It is replaced by new ice that forms on the bottom of the ice layer. As this new ice freezes, it releases heat directly into the underlying water.
The ice cap also traps solar heat in the lakes. But this contributes only about half as much heat as does the sublimation-freezing mechanism. Glacial meltwater brings in a little extra heat when it feeds the lakes in summer.
The fact that algae, bacteria, fungi, and protozoa thrive in these lakes does not mean comparable life forms live on Mars today. In fact, most scientists who have studied the Viking and other Mars-probe data doubt that the planet supports any life at all. But it might have had at least some kinds of microbes in the first 500 million or so years of its 4.5 billion-year existence.
Steven Squyres, a former Ames scientist now at Cornell University, considers the Antarctic lakes ``the closest analog on Earth to the Martian paleolakes.'' If microbes thrived in such Martian lakes billions of years ago, their fossils may pepper the layered sediments those lakes left behind -- sediments that show up clearly in Viking photographs.
The prospect of finding fossils intrigues Mars scientists almost as much as would the prospect of finding actual living organisms. It strongly reinforces their case for making Mars a top-priority scientific target and thus the premier solar system object for international planetary research.
NASA currently plans to put a survey satellite into orbit around Mars five years from now. A pair of Soviet probes should also study the planet and sample the Martian moon Phobos in the same time frame. But many scientists interested in Mars would like to make that planet the focus of joint Soviet/American research. Several missions, which would include placing a roving robot explorer on the planet and bringing back Mars samples to Earth, would precede a joint (American-led) manned expedition in the 21st century.
When Viking project veterans held a tenth reunion meeting in Washington this past July, Cornell University astronomer Carl Sagan pointed out that such research offers just the kind of ambitious but do-able goals that the American space program now needs to regain its scientific momentum. He explained that long-term dreams, such as colonizing Mars, provide no practical incentive, while short-term goals won't exercise American space capability vigorously enough. What's needed are goals that can be met but are currently just out of reach. Exploratory trips to Mars, preceded by sophisticated unmanned probes, would be just right, Sagan said.
This is the kind of advice the Reagan administration is hearing from many space scientists as it prepares for a summit meeting with the Soviets. The report of the National Commission on Space also emphasized Mars. Joint exploration of the planet would be a good focus for US-USSR cooperation. Both nations have much to contribute to such a program. It could be carried out in a manner that would not give the Soviets access to advanced United States technology, since each country could retain control of its own hardware. And, at this stage at least, it has no military implications. It's a good candidate for a summit agreement on space cooperation.
Robert C. Cowen is the Monitor's natural science editor.