IGPP Seminar Series

Detecting evidence of life in organic material on other worlds

by Chris McKay
Nasa Ames


For Mars (subsurface), Europa (surface ice) and Enceladus (plume) it is plausible that we will soon find organic material that may be remnants of past life. The challenge we will then face is the characterization of the organics that appear to be present. We know that there are organics in the outer solar system but they may all be non-biological in origin. Organic characterization, not life search (as done by Viking) is the relevant astrobiology science at this point for Mars, Europa and Enceladus. The organic characterization should be adequate to determine if the organics present plausibly result from biological processes rather than being part of the abiotic organics that are ubiquitous in the Solar System. The question can been addressed theoretically. I argue that natural selection has resulted in life on Earth specializing in the use of certain organic molecules in the construction of biomass - what I call the LEGO principle. The LEGO kit for life on Earth is the 20 L amino acids, the pyrimidines (U,T,C) and purines (A,G), the D sugars, a few lipids etc. The LEGO principle is likely to be common to any life form that has developed by natural selection. Hence one way to determine if a collection of organic material is of biological origin, is to look for a selective pattern of organic molecules similar to, but not necessarily identical with, the selective pattern of biochemistry in life on Earth. Implementing this search in practical terms in near term missions will require a sophisticated ability to separate and characterize organic molecules. Currently the instrument best suited for this task is a GCMS with solvent extraction. However, new methods of fluorescence and Raman spectroscopy could provide similar information and may have a role in future mission applications and remote applications.
Tuesday, 28 November 2006
3845 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM