also offer great flexibility; in any scientific investigation it is advantageous to be able to alter the analytical strategy as new information emerges. This is particularly critical in astrobiological investigations, where the characteristics of extraterrestrial organisms or prebiotic chemistry cannot be confidently predicted. Some analytical flexibility has been demonstrated in Mars Exploration Rover (MER) missions, in which adaptations of instrument protocols have been employed to analyze unexpected rock compositions, but changes in sample-handling capabilities and instrumentation are clearly impossible for investigations involving remote analysis by spacecraft.

BOX 5.1

Pros and Cons of Sample Return and In Situ Analysis

Mars sample return and in situ analyses both have advantages and disadvantages, as summarized below. The two are actually quite complementary.

Mars Sample Return

Pros. The factors favoring sample return include the following:

  • Ability to respond to discoveries or unexpected observations with new protocols and measurements;

  • Ability to repeat experiments by multiple laboratories and confirm key results;

  • Unlimited range of analytical techniques that can be applied;

  • No additional requirement for development of analytical instrumentation;

  • Much broader range of possible investigations;

  • Participation of entire analytical community;

  • Curation of samples for future investigations;

  • Potential to propagate organisms if they are discovered;

  • Strong complementarity with in situ analyses;

  • Greater ease of identifying and addressing analytical artifacts; and

  • Ability with limited mobility (i.e., by a static lander) to obtain a sample may be less costly.

Cons. The factors arguing against sample return include the following:

  • Expense, given that many technologies are not yet developed and the necessary costs are uncertain;

  • Requirement for infrastructure for containment and curation of samples on Earth;

  • Examination of samples outside their natural environment;

  • Planetary protection issues, such as those associated with, for example, forward contamination and biohazard certification;

  • Potentially small sample sizes and numbers, obviating investigation of many different samples;

  • Inherent complexity, and possible higher risk, of sample-return missions; and

  • Potentially complex sample packaging for Earth return.

Finally, sample return is particularly important for astrobiology investigations on Mars, since it is certain that any significant finding with potentially far-reaching implications will require corroboration by multiple replications of the same analyses (ideally in different laboratories and by different investigators) and by different types of analyses. Moreover, investigations with an astrobiological focus are likely to be a significant component of any future human exploration of Mars. In addition to being of the highest scientific priority in its own right, sample return by a robotic spacecraft has been identified in several NRC reports as being an important if not essential

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement