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Size Limits of Very Small Microorganisms: Proceedings of a Workshop (1999)

Chapter:Appendix B: Request from NASA

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Suggested Citation:"Appendix B: Request from NASA." National Research Council. 1999. Size Limits of Very Small Microorganisms: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/9638.

Appendix B
Request from NASA

National Aeronautics and Space Administration

Washington, DC 20548-0001

Reply to Attn of: SR

MAR 13 1998

Dr. Claude Canizares

Space Studies Board

National Academy of Sciences

2101 Constitution Avenue, N.W. Washington, DC 20418

Dear Dr. Canizares:

The investigation of the ancient Martian meteorite ALH84001 for evidence of life has revealed and highlighted a large degree of uncertainty in the possible existence of extremely small microorganisms here on Earth. The question of minimal microbial size is debated within the scientific community and there is no widely accepted theoretical minimum size for microorganisms. The Space Studies Board (SSB) has been a primary group advising NASA and seeks the Space Studies Board's advice concerning the size limits to life.

NASA has an interest in determining the current state of knowledge of the size limits to life on Earth, for microorganisms past and present, and in the theoretical limits. To understand the origin, evolution and distribution of life in the universe, a fundamental understanding of the size limits to life is needed. Scientists need to know what to look for and how to interpret the results. Considering the infancy of this research area and the continual advance in laboratory techniques, NASA also seeks recommendations concerning fertile research directions to explore the size limits to life.

In addition to considering the size below which life is not possible, there are related issues that should be addressed. What is the relationship between minimal size and the environment? Are very small microorganisms primitive or is their size a derived characteristic? What are the implications to the search for life on other planets?

Your help in addressing the questions about the size limits to life is greatly appreciated. Dr. Michael Meyer will be working with you and the SSB staff to finalize a Statement of Task for this study effort. Please contact him (202-358-0307) if you need further information about this request.


Wesley T. Huntress, Jr.

Associate Administrator for Space Science

Suggested Citation:"Appendix B: Request from NASA." National Research Council. 1999. Size Limits of Very Small Microorganisms: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/9638.
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How small can a free-living organism be? On the surface, this question is straightforward-in principle, the smallest cells can be identified and measured. But understanding what factors determine this lower limit, and addressing the host of other questions that follow on from this knowledge, require a fundamental understanding of the chemistry and ecology of cellular life. The recent report of evidence for life in a martian meteorite and the prospect of searching for biological signatures in intelligently chosen samples from Mars and elsewhere bring a new immediacy to such questions. How do we recognize the morphological or chemical remnants of life in rocks deposited 4 billion years ago on another planet? Are the empirical limits on cell size identified by observation on Earth applicable to life wherever it may occur, or is minimum size a function of the particular chemistry of an individual planetary surface?

These questions formed the focus of a workshop on the size limits of very small organisms, organized by the Steering .Group for the Workshop on Size Limits of Very Small Microorganisms and held on October 22 and 23, 1998. Eighteen invited panelists, representing fields ranging from cell biology and molecular genetics to paleontology and mineralogy, joined with an almost equal number of other participants in a wide-ranging exploration of minimum cell size and the challenge of interpreting micro- and nano-scale features of sedimentary rocks found on Earth or elsewhere in the solar system. This document contains the proceedings of that workshop. It includes position papers presented by the individual panelists, arranged by panel, along with a summary, for each of the four sessions, of extensive roundtable discussions that involved the panelists as well as other workshop participants.

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