In a similar vein, this report of the Space Studies Board's Task Group on Sample Return from Small Solar System Bodies considers whether samples returned to Earth from small solar system bodies might harbor living entities that could harm terrestrial organisms or disrupt ecosystems.

SCOPE AND APPROACH OF THIS STUDY

Because only self-replicating entities could pose a significant danger to terrestrial organisms and ecosystems,1 the task group focused on the following topics:

  1. The possibility that, at some time in the past, life originated on a body from which a sample might be taken, or that life was transported there from elsewhere in the solar system;

  2. The possibility that life still exists on the body either in active or in reactivatable form; and

  3. The potential hazard to terrestrial ecosystems from extraterrestrial life if it exists in a returned sample.

Assessing the potential for biological contamination of Earth by organisms present in samples returned from small solar system bodies requires identifying the range of conditions under which life can originate, as well as the environmental extremes that can be tolerated by metabolically active and inactive life forms. Life originates at the transition from a world of minerals and abiotically synthesized organic compounds to one of organic-based self-replicating systems capable of evolving by natural selection. This report recognizes forms of life that are composed of organic compounds and are dependent on organic chemistry; the task group had no relevant information for considering any other forms.

There is no direct evidence indicating that a living entity evolved or exists on small solar system bodies. Therefore, this report examines indirect evidence based on data from Earth, meteorites, other planets, the Sun, and the Moon and on astronomical observations of distant objects in an effort to assess whether NASA needs to treat samples returned from small solar system differently from samples returned from Mars. The quality of the available data varies for each type of small solar system body examined in this report. For example, far more data are available on the structure, composition, and history of the Moon than for any other body. The task group began by reviewing what is known about the origin of life on Earth, the conditions for the preservation of metabolically active organisms in a terrestrial environment, and the somewhat different conditions needed to preserve living organisms in an inactive form. It then attempted to generalize from terrestrial experience and to outline general requirements for the origin and survival of life that would apply on any solar body.

Based on this analysis, the task group identified six parameters (Box 1.1) as relevant to the assessment and arranged these parameters in a rough order of importance, while recognizing that the order might change somewhat depending on the solar system body being assessed.

A key concern of the task group was the identification of returned samples that do not require containment,2 because containment has important financial and scientific implications for mission planning. Based on the six parameters identified as relevant, the task group formulated a series of questions as a basis for identification of whether or not samples require containment. These questions were used to assess the potential for a biological entity to be present in or on samples returned from planetary satellites, asteroids, comets, and cosmic dust. Based on the answers to these questions, the task group derived findings that it then analyzed with respect to their implications for sample containment and handling. The task group considered only two possible containment and handling requirements: either (1) strict containment and handling as outlined in the Mars report (NRC, 1997) or (2) no special containment beyond what is needed for scientific purposes. (Sample handling requirements to support scientific investigations are currently under study by NASA.) The task group ruled out intermediate or compromise procedures involving partial containment. In certain cases (e.g., P- and D-type asteroids) the limitations of the available data led the task group to be less certain, and therefore more conservative, in its assessment of the need for containment.

1  

 See NRC (1997) for a discussion on the potential for pathogenesis (toxic effects of microorganisms and infectious agents).

2  

 The terms "contained" and "containment" are used in this report to indicate physical and biological isolation and handling of returned samples as specified for samples returned from Mars (see NRC, 1997).



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