The Importance of Scientifically Selected Sample Suites to Achieving Mars Returned Sample Science Objectives

In order to realize the full scientific potential of the first samples that could be returned from Mars, it will be necessary to go far beyond that which can be learned from individual, geologically unrelated samples. It is absolutely vital that sample "suites" (defined here as a set of samples that are connected by a biogeophysical process) be strategically designed, selected, cached and returned using the best available context data and full understanding of the objectives that we hope to achieve. A premise of sample suites is that the differences between samples may be more important than the absolute value of any of them.

Most of the science objectives for Mars Sample Return (MSR), as they are currently envisioned, cannot be adequately addressed by a single sample or data point. The geological settings of greatest interest to a potential MSR campaign to answer the most important astrobiological and geological questions are heterogeneous, but in ways that vary systematically. Many of the processes that formed such settings can only be understood by examining variability among geologically and petrologically related samples (e.g., unraveling spatial, compositional and temporal gradients). For example, in sedimentary settings interpretations of depositional settings and paleoclimate/climate change rely on evaluating both spatial and temporal (stratigraphic and sedimentological) relationships. In hydrothermal settings constraining fluid pathways and temperature history (thus identifying the most habitable niches) requires the mapping of mineralogical and geochemical gradients, often over significant distances. And in volcanic settings, it is often necessary to define liquid lines of descent (associated with fractional crystallization) with multiple petrogenetically related samples to evaluate magmatic processes and source characteristics. An individual sample taken from such complex geological settings, would only sample single points in multi-dimensional (spatial, temporal, composition, temperature, etc.) complex systems, and thus would be inadequate for evaluating many of the most important processes. Understanding the variation between samples collected as part of a well-designed and complete sample suite is the best way to develop a more complete understanding of Mars as a system.