In the mid-1990s the U.S. embarked on a new strategy for exploring the Red Planet. In response to the 1993 failure of the Mars Observer mission—a billion-dollar, decade-in-the-making probe that mysteriously lost contact with ground controllers just before it was scheduled to go into orbit around the planet—NASA administrator Daniel Goldin decided to shift to smaller, less expensive spacecraft and create a sustained exploration campaign by sending one or two probes to Mars at every launch opportunity. (These opportunities come every two years or so, when Earth and Mars are properly aligned.) The new strategy spread out the inherent risk of interplanetary travel and ensured that the engineering experience and scientific data acquired by one mission could be rapidly used by the next. The approach has proved a brilliant success, putting three NASA spacecraft into orbit around Mars and three rovers on the planet’s surface (Pathfinder, Spirit and Opportunity). The Phoenix Mars Lander, which left Earth in August, is expected to reach the Red Planet next May, and NASA plans to launch the Mars Science Lab in 2009.
Subsequent missions are in jeopardy, however. Alan Stern, associate administrator for NASA’s Science Mission Directorate, warned in July that at least one of the future Mars probes may have to be scrapped to free up funding for a much costlier mission, tentatively scheduled for the 2018–2020 period, that would collect samples of Martian rock and bring them to Earth. Moreover, highly placed scientists and program leaders report that the new plan may actually require the sacrifice of all other Mars spacecraft after 2009.
Putting aside the question of whether the redirected funds would actually be devoted to the Mars Sample Return (MSR) mission, such a reorganization would be a very bad idea. A one-shot mission to bring Martian rocks to Earth for laboratory analysis is not really a good way to address the central question of Mars science. The Red Planet is a critical test bed for the hypothesis that life is likely to arise wherever the appropriate physical conditions—notably, the presence of liquid water—prevail on a planet for a sufficiently long time. Scientists now know that Mars probably had standing bodies of water on its surface between three billion and four billion years ago, when there was already plentiful microbial life on Earth. Because asteroid and comet impacts facilitate the transfer of rocks between Mars and Earth, the discovery of microfossils on the Martian surface would not in itself prove that life arose independently on Mars. To settle the question, researchers would need to find living organisms on the planet and examine their biochemistry. These organisms, if they exist, are most likely to be found in groundwater. Thus, the most important goal of the exploration program is to identify sites on Mars where groundwater is within practical drilling distance of the surface. This task can best be done not with an MSR mission but with a comprehensive scouting program involving orbiters, rovers, drillers and robotic aircraft with ground-penetrating radar.
Furthermore, even if one concedes considerable importance to the MSR mission, it is doubtful whether the reorganization plan is the right way to get there. If NASA halts its Mars exploration for a decade, all the best people will leave the team and be replaced by those who enjoy drawing charts and schedules. Instead of wrecking the current Mars program and hoping for the best, the space agency should build on it. New orbital spacecraft and aircraft should extend the reconnaissance of the Red Planet and identify sites containing potential fossils and near-surface groundwater. With such discoveries building well-justified public interest, NASA will be able to ask for extra funding to add an MSR mission to the queue. While the space agency is preparing the mission, it can send rovers and drillers to the most promising sites and cache samples that could reveal the truth about life on Mars. In addition to providing major scientific discoveries, such a mission might well give NASA the boost it needs to send human explorers to the Red Planet.