Sample-return missions are technologically very challenging. Much must be accomplished in the years between now and the putative earliest date (2011) when the first sample-return mission might be launched. COMPLEX urges that NASA redouble its efforts to develop the essential technologies and infrastructure necessary to make the first sample return a reality in that time. The sample-return strategy is ambitious and exciting, but as currently defined, it depends on numerous technologies and strategies that have not been attempted before. These include precision landing and surface operations, a robust Mars sample collection and containment capability, a Mars ascent vehicle, a strategy for reliable sample recovery and Earth return, and an Earth-based quarantine facility with plans for sample handling and sample distribution to the sample analysis community.

An important question concerns the timing of sample return. There are two different points of view about when the first sample-return mission should be flown. From one perspective, because the technological and cost requirements are so great for sample-return missions, it is essential for the first sample returned to contain vital information relative to the biological potential of Mars. The other perspective is that a state of diminishing returns has been reached (after the missions through 2005) in acquiring data to identify promising sites; enough is known now to select fruitful sites, and the best strategy is to move to sample return as quickly as possible to guide future Mars exploration. COMPLEX elaborates below on these disparate viewpoints.

The first viewpoint argues that it is likely that the costs of sample return will be high, both in spacecraft resources and in the Earth-based infrastructure to receive and house the samples, and therefore that the number of sample-return missions flown will be small. Sample return should be deferred, therefore, until everything has been done that can be done with remote sensing and through numerous in situ measurements of key indicators such as reduced carbon, to ensure that the samples with the most compelling potential to answer the question, Did life ever arise on Mars?, are obtained. Underlying these arguments, to some extent, is the fear that without the reassurance of exhaustive remote-sensing surveys, the first samples returned may turn out to be indistinguishable from SNC meteorites, and that in such a case, further support of sample return would be jeopardized.

Those with the opposing point of view hold that enough will be known from remote sensing and in situ measurements by 2011 to mount a fruitful mission, and that sample return should be expedited. By the end of the 2005 missions, most of the critical measurements that are needed to guide surface sampling will have been made from orbit. However, the true meaning of the remotely acquired data will not be fully understood because of the lack of ground-truth. Landed science missions will provide some ground-truth, but they are no substitute for the laboratory examination of surface materials. Experience on Earth and on the Moon has shown that significant advances in exploiting remotely sensed data require integration with samples and a knowledge of surface properties. Early sample return will be essential for optimizing future efforts to find the most compelling biological sites. Experience must be gained in the technically complex and risky activity of collecting and returning martian samples, in the process maximizing the value of the remotely acquired data sets for future exploration. Those in this camp argue that it is by the second or third sample-return mission, with attendant periods during which data are evaluated, that the most compelling sites are likely to be revealed and sampled.

COMPLEX emphasizes that answering the question, Did life ever arise on Mars?, must be approached from a broad understanding of the planet and its history. Investigators must be as prepared for an answer of no as well as for yes. It is the committee’s view that the goal of the “wait for a perfect sample” viewpoint is too narrow in scope; that approach risks failure if an uninformative sample is in fact returned, and it risks interminable delays if the remotely acquired orbital and in situ data are held by some to be equivocal.

COMPLEX notes that sample return “as soon as possible” will not occur all that soon (=2011), and in the interim there is time to make additional remote-sensing measurements in support of the first sample return. The committee argues (see Chapter 11) that, with or without additional remote-sensing studies, there is no danger that the surface samples returned by the first mission will be identical to SNC meteorites, or that they will be uninteresting, whether or not they contain evidence bearing directly on the question of martian life.