Vision and Voyages for Planetary Science in the - Solar System ...

experiments, compounded by the uncertainty regarding the nature of possible martian life and issues of
terrestrial contamination, would be difficult and carries very high scientific risk.
Discoveries by MSL could provide additional justification for sample return, but are unlikely to alter
the basic architecture of sample return, in which the primary system variables—the sample site and the
samples that are collected—are not constrained in the proposed architecture. Similarly, the lack of major
new discoveries by MSL would not impact the importance of getting samples back to Earth, and may well
increase the importance of collecting and studying samples in terrestrial labs where a much broader suite
of measurements could be obtained.
Experience based on previous studies (e.g., of meteorites, the Moon, cometary dust, and the solar
wind) strongly supports the importance of sample analysis. Such a diversity of techniques, analysis over
time, improvements in sensitivity, and new approaches available in terrestrial labs are expected to
revolutionize our understanding of Mars in ways that simply cannot be done in situ or by remote
sensing. 81,82
Site Selection and Context
The information needed to select a sample return site that would address high-priority science
objectives has been, or can be, acquired with current assets.
Mars is a remarkably diverse planet with a wide range of aqueous environments preserved in its rock
record. As a result of two decades of orbital and in situ exploration of Mars, a large number of excellent
candidate sample return sites, where water played a major role in the surface evolution, have already been
identified. Significantly, the geologic setting of these sites—as identified through mineralogic and
stratigraphic mapping—indicate that there were major differences in water chemistry and temperature,
weathering processes, and sediment transport and deposition processes across Mars, providing a diversity
of environments from which to collect samples. The known sites also contain diverse sedimentary and
igneous terrains within the roving range of existing spacecraft.
The site will be selected on the basis of compelling evidence in the orbital data for aqueous processes
and a geologic context for the environment (e.g., fluvial, lacustrine, or hydrothermal). The sample
collection rover must have the necessary mobility and in situ capability to collect a diverse suite of
samples based on stratigraphy, mineralogy, composition, and texture. 83 Some biosignature detection,
such as a first-order identification of carbon compounds, should be included, but it does not need to be
highly sophisticated, because the samples will be studied in detail on Earth. 84
Sample Criteria
Selecting and preserving high quality samples is essential to the success of the sample return effort.
MEPAG identified 11 scientific objectives for Mars sample return (MSR) and specified the minimum
criteria for the sample to meet these objectives. 85 The collection of Mars samples will be most valuable if
they are collected as sample suites chosen to represent the diverse products of various planetary processes
(particularly aqueous processes), and addressing the scientific objectives for MSR will require multiple
sample suites. A full program of science investigations is expected to require samples of >8 g for
bedrock, loose rocks and finer-grained regolith and 2 g. to support biohazard testing, each for an optimal
size of 10 g. 86 Textural studies of some rock types might require one or more larger samples of ~20 g.
The number of samples needed to address the MSR scientific objectives effectively is 35 (28 rock, 4
regolith, 1 dust, 2 gas). In order to retain scientific value, returned samples must be fully isolated and
sealed from the martian atmosphere, each sample must be linked uniquely to its documented field context,
and rocks should be protected against fragmentation during transport. The encapsulation of at least some
samples must retain any released volatile components. 87
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