Living organisms represent a subset of the organic molecules that exist in the solar system and beyond. Analyses of meteorites, the atmospheres of the giant planets and Titan, and the surfaces of outer solar system bodies reveal a range of abiotic chemical processing of organic molecules. Detection of simple organic molecules (e.g., methane) has been accomplished for the atmospheres of very cool brown dwarf stars, an important precursor to a protocol for the eventual remote spectroscopic assessment of the habitability of extrasolar planets.
Although the vast bulk of the analysis performed to date on extraterrestrial samples demonstrates the non-living origin of these organics, the small enantiomeric excess in the Murchison meteorite remains a contentious puzzle. Whether it suggests the action of abiotic processes to introduce asymmetry into an abiotic stereochemical system, or some sort of postimpact terrestrial process acting on the meteoritic organics, is unresolved. In the case of Mars, the failure of the Viking landers to detect organic molecules was key to the conclusion that the Viking life detection experiments were seeing abiotic processes in a highly oxidizing soil, rather than metabolism. Terrestrial laboratories are capable of detecting and characterizing very small amounts of organic molecules in samples, as well as reliably determining whether the molecules are indigenous to the sample or a terrestrial contaminant. This was of particular value in analyzing the SNC meteorite ALH84001, in which it was found that most of the organic material is a terrestrial contaminant and the remainder resembles primitive meteoritic or interstellar material.
The development of more sensitive techniques to detect organic molecules and characterize the extent to which organic chemical systems may be evolving toward life in a planetary environment is an important priority. Many organic-rich environments in the solar system will be accessible to in situ analysis in the coming couple of decades but are prohibitively difficult targets for sample return (e.g., the surface of Titan). It is therefore desirable to miniaturize the instruments necessary for sensitively detecting and characterizing organic phases so that they can be accommodated on spacecraft dispatched to a variety of solar system targets.
The committee concludes that it is crucial to continue the development of techniques to detect and analyze in situ organic chemical systems of either biotic or abiotic origin, with the goal of increasing the techniques' sensitivity and diagnostic capability.
1. Space Studies Board, National Research Council, Preventing the Forward Contamination of Europa, National Academy Press, Washington, D.C., 2000.
2. See, for example, Space Studies Board, National Research Council, The Quarantine and Certification of Martian Samples, National Academy Press, Washington, D.C., 2002.
3. Space Studies Board, National Research Council, Assessment of Mars Science and Mission Priorities [prepublication text], National Academy Press, Washington, D.C., 2001.
4. M.H. Carr in Water on Mars, Oxford University Press, New York, 1996, pp. 180-183.