Even before the recent announcement of the possible detection of ancient life in a martian meteorite, Mars was an object of high scientific priority and immense public interest. Indeed, anyone doubting that Mars holds a special place in the human imagination need only look to the recent phoenixlike rebirth of NASAs plans for the exploration of the Red Planet. NASAs hopes and dreams of exploring Mars, on hold since Viking in the late 1970s, were embodied in Mars Observer, which just hours before entering orbit around Mars in August 1993 ceased all communications with Earth. For scientists, years of effort were scuttled with the very public failure of this sophisticated and expensive probe. For policymakers, it was yet another addition to the ever-growing litany of NASA woes.
Today, with the imminent launch of Mars Pathfinder and Mars Global Surveyor missions, Mars exploration is about to be renewed. Moreover, Congress has already approved Mars Surveyor, a program to dispatch a pair of Mars-bound spacecraft every 26 months until 2005.
What changes hallowed this rebirth? The basic answer is that NASA's Mars program in 1996 is smaller, faster, and cheaper than its counterpart of a few years ago. While Mars Observer cost more than $600 million and took almost a decade to design and build, the new-style Mars missions are capped at about $100 million apiece and must be designed and launched in just a few years.
While the smaller, cheaper, faster mantra is widely invoked as a new way to explore space, is it anything more than a slogan? Can a series of small missions spread out over a decade produce sufficient scientific return to justify the still-significant cost? This question was the subject of a recent report published by the National Research Councils Committee on Planetary and Lunar Exploration (COMPLEX).*
Before answering this question, we must be clear about why we are studying Mars. It makes no sense to spend $100 million or more on stunts. Missions must lead to a substantial improvement in our understanding of the planet most like Earth and the obvious target for human exploration beyond the Moon.
The three most important scientific topics to be addressed by future missions to Mars are: Why has Mars's climate evolved so differently from Earths and why, in particular, is Mars so much drier and colder than in the past? How have geological processes created a martian landscape so similar to Earth's in some aspects and yet so different in others? Does evidence prebiological organic compounds or even extinct life remain on Mars?
Mars Global Surveyor, scheduled for launch in November, will use spare copies of many of Mars Observers instruments to monitor the martian atmosphere, map the composition and topography of its surface, and study the planets magnetic field. Mars Pathfinder, scheduled for launch in December, will land a science package, including a small roving vehicle, on Mars next July. Subsequent missions in 1998 and 2001 will carry the remainder of Mars Observers instruments and will conduct more complex observations, both on the edge of Marss southern polar cap and from orbit.
The first few Mars Surveyor missions will measure the global characteristics of the wind-blown soil and well-mixed atmosphere. Access to martian rocks will be limited to the immediate vicinity of landing sites, yet evidence for past climate changes and ancient life, if any, is most likely to be embedded within rocks, probably in at most a few locales. Thus Mars Surveyors inability to study a diverse sample of rocks and terrains is a major shortcoming.
An equally great worry is that Mars Surveyor includes no provision for designing and constructing innovative instruments. Can this program be smaller, faster, and cheaper if it must rely on bulky instruments using 1970s technology?
A longer-term concern is that as the program progresses it may become increasingly difficult to make major discoveries with the small landers currently envisaged. Larger landers--those capable of transporting sophisticated, long-range rovers to the surface--will be required for future missions. This is especially true for the Holy Grail of Mars exploration, a mission to return multiple samples of martian soil and rock to Earth for analysis. Although NASA has penciled in the launch of such a mission for 2005, its feasibility is uncertain.
Despite some shortcomings, Mars Surveyor holds great promise for enhancing our understanding of Mars' atmosphere and climate, its geological characteristics, and, to a somewhat lesser extent, its present and past potential for harboring life. This aggressive and exciting program deserves the full support of scientists and public alike.
*Copies of this report, Review of NASAs Planned Mars Program, are available upon request from the Space Studies Board (phone: 202-334-3477).
(Burns, of Cornell University, and Greeley, of Arizona State University, are respectively the past and present chairs of COMPLEX. Smith, of the NRC, directs the Committees activities.)