THE first human footfall on Mars still lies in the indefinite future. But robotic study of that intriguing planet is entering a phase that could be the next best thing to being there.
Encouraged by this prospect, planetary explorers are dreaming ambitious dreams they can reasonably expect to fulfill over the next couple of decades.
They hope to gain an intimate on-site knowledge of the Red Planet by studying it from the outside in. That's why they view the arrival next week (Aug. 24) of the National Aeronautics and Space Administration (NASA) Mars Observer spacecraft as just the beginning of a new saga of planetary exploration.
Mars Observer is to produce a geological map of the entire planet, including the mineral composition of its surface. It is to follow Martian climate through at least one full Martian year (687 Earth days) of seasonal cycles. That's the outside view. It should yield a wealth of new scientific knowledge.
But the big payoff will come when advanced robotic explorers reach the surface to verify what Mars Observer sees from orbit and gather the kind of intimate detail that "down-in-the-dirt" geologists probe for on Earth. That's what the planners' dreams are about.
They already have at least one - and probably two - such follow-up missions in hand. Russia's Mars '94 mission, now due to head for the Red Planet in November 1994, is to deposit two instrumented landers and two ground-penetrating probes. Like Mars Observer, this is a mission with wide international participation on its scientific team. Meanwhile, NASA's fiscal 1994 budget, now awaiting Senate approval, includes funds for a "Pathfinder" mission with a simple landing craft that would deploy a small robot rover.
Farther down the line, Russia hopes to launch another international mission in 1996 that would also deploy a robot rover plus a French instrumented balloon. But Mars '96 is not yet fully funded.
It's beyond these approved - or nearly approved - missions that the dreaming of planners such as Roger Bourke starts. Dr. Bourke is manager for Mars advanced missions at the California Institute of Technology's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. JPL manages these programs for NASA.
To begin with, Dr. Bourke and his colleagues see the Pathfinder mission as a "proof of concept" for what they call the Mars Environmental Survey (MESUR) program. This would land a network of ground stations for long-term surface observations, including seismic monitoring. A fleet of relatively inexpensive spacecraft would carry these stations directly to the Martian surface.
Looking further ahead, Bourke suggests it may also be possible to use MESUR to return a Martian surface sample to Earth. A unit tucked into a MESUR package might be able to grab a sample and carry it to an orbiting mother ship that would bring the material home.
Bourke notes that rocks have "a memory of what went on early" in the planet's geological history. The kind of extensive analysis that could be done in earthly laboratories could reveal that history, including any evidence that Mars once had surface water.
Yet Bourke explains that sample return is, at best, "ambitious and difficult" and, at worst, "may not be affordable." One alternative might be a fleet of balloons that would carry instruments to analyze the surface at relatively close range over wide areas.
The French balloon on the Mars '96 mission would begin this kind of exploration.
But balloons go where the wind takes them. Bourke suggests that remote-controlled survey aircraft being developed to fly in Earth's upper atmosphere probably could also operate on Mars.
Right now, these are speculative ideas. Yet, as Bourke notes, "it's interesting to see the technologies of balloons, airplanes, and microelectronics opening new ways for exploration." That kind of "dreaming" could become practical reality over the next 20 years.