The committee recognizes that life may never have started on Mars or gained a foothold there. However, the search will lead to a broad understanding of the planet as a whole. It requires investigation of the geological and geophysical evolution of Mars, the history of volatiles and climate, the nature of the surface and the subsurface, the history and geographical distribution of liquid water, and the availability of other resources that are necessary to support life, as well as of the processes that controlled each of these. The search also requires a detailed understanding of the nature of terran life and how it functions in different environments.

The Priority of the Search for Life on Mars

Although it is not the only possible emphasis for the Mars program, astrobiology provides a scientifically engaging and broad approach that brings together multiple disciplines to address an important set of scientific questions that also are of tremendous interest to the public. And, more than any other scientific focus, it integrates the disciplines together into a coherent approach to understanding Mars as a planet.

Finding. The search for evidence of past or present life, as well as determination of the planetary context that creates habitable environments, is a compelling primary focus for NASA’s Mars Exploration Program.

A Broad Approach to the Search for Life on Mars

Addressing astrobiology science goals requires a broad approach to understanding Mars. It involves not just searching for present and past life, but also understanding the geological and environmental context that determines planetary habitability. It will entail determination of the geological and geochemical evolution of the planet, its internal structure, and the nature of its interaction with the space environment. Such an approach will provide the information necessary to be able to apply the results to assessing the potential for life throughout the galaxy. In addition, because of the interconnected nature of the martian geological, geochemical, geophysical, and climatological systems, a broad approach will likely enable astrobiologists to determine which characteristics result from nonbiological processes and which result from biological processes and so could be used as biosignatures. While most aspects of Mars exploration have connections to astrobiology, the emphasis should be on those areas that are most directly related to habitabilitythe potential for life and the presence of its building blocks, and the possible occurrence of life.

NASA’s 1995 report An Exobiological Strategy for Mars Exploration took the approach of starting from the global perspective and focusing increasingly on the local perspective. This approach involved a series of steps:

  1. Global reconnaissance that focused on the history of water and the identification of sites for detailed in situ analysis;

  2. In situ analysis at sites that hold promise for understanding the history of water;

  3. Deployment of experiments that address astrobiology science questions, including the nature of martian organic molecules and the presence of features indicative of present-day or prior life;

  4. Return of martian samples to Earth for detailed study; and

  5. Human missions that would provide the detailed geological context for astrobiology measurements and the detection of modern-day “oases” for life.

This reasoned and measured approach provides the best opportunity for determining the geological and geochemical context in which the most useful and appropriate astrobiological measurements can be determined, implemented, and then properly interpreted and understood. It combines a broad, interdisciplinary approach to understanding Mars as a whole with the detailed, focused investigations that allow researchers to understand the astrobiology of Mars.

Finding. The search for life and understanding the broad planetary context for martian habitability will require a broad, multidisciplinary approach to Mars exploration.

Finding. At the same time, the astrobiological science goals can best be addressed by an implementa-



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