MARS, the classical symbol of war, has become a modern symbol of peaceful cooperation - and competition - between the United States and the Soviet Union. The space cooperation agreement signed April 14 by US Secretary of State George Shultz and Soviet Foreign Minister Eduard Shevardnadze cites 16 specific areas for initial cooperative projects. The first four - and hence the most prominent of these provisions - focus on Mars.
They provide planetary scientists of both countries a formal means through which to access each others' planned Mars missions. This includes next year's Soviet mission to study the Martian moon Phobos and the US Mars Observer mission to survey the planet from orbit, scheduled for 1992. The agreement also assures the Soviets of help from the US Deep Space Network for precision tracking of their Mars spacecraft - an important asset for a mission which plans to hover close to a tiny Martian moon.
Both the prospect of cooperation with the Soviet Mars program and the international competition it provides have moved Mars exploration high on the agenda of the National Aeronautics and Space Administration (NASA). Geoffrey A. Briggs, director of NASA's solar system exploration division, stressed the competitive element when he spoke at the 18th Lunar and Planetary Science Conference, which met in Houston last March. ``It's clear to me that we shouldn't plan on leaving the inner solar system - and Mars in particular - to our colleagues to explore,'' he said.
Soviet space officials are talking freely around the world about exploring Mars intensively with a view, ultimately, to sending human survey teams. They're inviting other nations to join them. Brazil and several European countries have accepted. Now the US is set to cooperate.
Next year's mission is bold enough to attract many scientists. Mars has two tiny moons - Phobos (Fear) and Deimos (Dread) - repectively measuring 11.2 miles by 13.7 miles and 7.5 miles by 8.1 miles in their shortest and longest diameters. They may be captured carbonaceous chontrites - asteroids containing organic matter. The Soviet probes will come close enough to Phobos to probe its surface with radar, blast off samples with laser beams, and drop instruments.
This is the only Soviet Mars mission fully authorized at this time. But a mission called Vesta, to be launched in 1992, is far enough along in planning to be mentioned in the US-USSR agreement. It would survey Mars itself, drop penetrating probes into the planet's surface, and release a balloon carrying instruments in its atmosphere.
At the Houston conference, Valery Barsukov, director of the USSR Academy of Sciences' Vernadsky Institute for Geochemistry and Analytic Chemistry, described planning for other Mars missions. There are design studies of a small robot rover that might also be dropped during the Vesta mission. It would run over the surface with instruments and cameras. A larger rover might then be sent on a follow-up mission in 1994. The Soviets also are interested in returning samples of Martian rocks, soil, and air to Earth. Such a mission could come as soon as 1996, although 1998 is a more likely date, according to Mr. Barsukov.
For the US, the Mars Observer is the only Mars game in town. The spacecraft would observe Mars from polar orbit for a full Martian year (687 Earth days). It would study the planet's climate and map its surface composition. Supporters of the project find it ironic that, on the very day the US and USSR signed their space cooperation agreement, NASA reaffirmed its intention to postpone the Mars Observer launch from 1990 to 1992. These supporters continue to lobby for the earlier launch date.
NASA, nevertheless, has begun to plan aggressively for an expanded Mars program. It has announced that eventual human exploration of Mars preceded by robotic missions, including sample-return, is one of four major space initiatives being considered. The others are enhanced general exploraton of the solar system, expanded study of earth, and a permanent scientific base on the moon.
The Johnson Space Center in Houston and the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., are heavily involved in the planning. They expect to issue study contracts to industry by early autumn. They're starting with a ``baseline'' mission for launch in 1998 in which a robot craft would return 11 pounds of rock, soil, and atmosphere to Earth by 2001. It would include a roving vehicle to gather samples and survey the Martian terrain. Both the National Academy of Sciences and NASA advisory committees have recommended this project.
The planners' ambitions take off from there. With presidential approval, they would like to design an accelerated program with the sample-return mission moving up to around 1996. Many projects similar to those contemplated by the Soviets would be included, such as subsurface probes and balloon-borne instruments. In fact, the prospect of cooperating with the Soviets, especially in a sample-return mission, is an added reason for speeding up the American program. NASA is including this proposal as part of a new initiatives package it hopes President Reagan will act on this year.
Without a presidential commitment to a more extensive and more expensive space program than the US has mounted in two decades, NASA's ambitious Mars planning will likely come to nothing. Even its present program exceeds the agency's financial grasp.
JPL director Lew Allen Jr. has noted that just to carry out this current program, including the space station, ``at a reasonable pace'' would require ``perhaps as much as a 50 percent'' increase in the NASA budget. ``But that,'' he told the Houston conference, ``seems somewhat unlikely, under the kind of budget pressures that existed in the past.'' The statement by NASA Administrator James Fletcher that shortage of funds may delay relaunch of the shuttle program underscores Dr. Allen's point.
Meanwhile, as Bruce C. Murray observes, ``The Soviet Union is on a roll and is doing some very good things in interplanetary space.'' A planetary scientist at the California Institute of Technology and a former director of JPL, Dr. Murray adds ruefully, ``What they're going to do on Mars are things we thought about doing, but didn't do, 10 years ago.''
Unlocking clues to the Red Planet
FIFTY percent farther from the Sun than is Earth, and about half the size of our planet, Mars tantalizes solar system explorers. The partial answers they now have to two major questions - does Mars have water and life - make them eager to learn more.
Does Mars have water? The answer is ``yes.'' Now the issue is how much water and where is it located. Does Mars have life? The tentative answer is ``probably not,'' although that's not certain. But if Mars has no life now, it may well have evolved at least primitive life forms in the distant past.
The Martian surface today is a forbidding environment. With only about 1/10th the mass of Earth, Mars has only 38 percent of Earth's surface gravity. The largely (95.3 percent) carbon dioxide (CO2) atmosphere has a surface pressure of about half a percent of sea-level air pressure on Earth. Winds in this thin air often stir up planet-engulfing dust storms from the waterless ground when Mars comes closest to the Sun. The global average temperature is a frigid minus 53 degrees C. (minus 63 degrees F.).
While a Martian day is only 40 minutes longer than a day on Earth, the Martian year is 1.88 Earth years long. The seasons of this long year are most noticeable in the waxing and waning of the polar caps. These are deposits of solid CO2 (dry ice). The CO2 atmosphere is in equillibrium with these caps. So the surface air pressure on Mars varies by 20 to 30 percent from season to season as the polar caps release CO2 and freeze it out of the atmosphere again.
There's no doubt Mars has water. Photographs show water ice beneath the north polar CO2 cap. Scientists suspect it exists under the south polar cap and probably elsewhere below ground.
Also, water-cut channels and what appear to be old lake-bottom sediments suggest massive amounts of water have existed on the surface. Floods may have surged at rates up to 10,000 times the average discharge rate of the Mississippi River, to judge from the channels.
Scientists specify a planet's water inventory in terms of the depth of the ocean it would form if spread uniformly over the planet. This amounts to 3 kilometers (1.86 miles) for Earth. For Mars, estimates range from as little as 6 meters (19.7 feet) to over 500 meters (546.5 yards). Reviewing these estimates recently in the magazine Nature, Mars specialist Michael H. Carr of the US Geological Survey concluded that, on balance, the higher estimates are more likely than the lower figures. This would mean that, while Mars has much less water than Earth, it still has produced considerable water. Much of this probably is still there as subsurface water and ice, making the distribution of Martian water a major target for both unmanned and, eventually, manned exploration.
Dr. Carr also noted that Mars may have had a thicker, CO2-rich atmosphere in its early years than it has today and may have had a relatively warm, wet climate. This could have been hospitable for the rise of organic life.
The Viking robot scientific stations, which landed in 1976, turned up no sign of life. Given Mars' desolate terrain, scientists are skeptical about ever finding living organisms. Yet the obvious signs of long-vanished lakes and water courses make many planetary biologists wonder what might once have lived there.
Studies of permanently frozen Antarctic lakes, where microbes thrive in water capped by 10 to 15 feet of ice, whet their interest. Similar ice-capped lakes might have allowed primitive organisms to evolve on Mars early in that planet's history. They conserve water and provide a warm environment even in frigid, bone-dry surroundings.
The Antarctic lakes exist in so-called dry valleys where there's less precipitation than in the Gobi desert and air temperatures average minus 20 degrees C. (minus 4 degrees F.). But water temperatures below the ice caps reach as high as 25 degrees C. (77 degrees F.).
Virginia Tech's George Simmons Jr., who has explored one of these lakes, says, ``When you go through this ice, it's like being in a time warp in which you ... look at the environment that existed before higher organisms evolved.'' He speculates that, if microbes did evolve on Mars, their fossils probably pepper the ancient lake sediments which show up clearly in photos of the Martian surface. This puts the sediments high on the list of materials a sample return mission would send back to Earth.