The recent claims by three teams of the existence of methane (CH4) in Mars implied the 
possibility of life beyond Earth. This concept was strengthened with the recent discovery of 
“extremophiles”, terrestrial microorganisms capable of existing under conditions that most 
living things cannot tolerate. However, a more robust determination of habitability and the 
presence of life will require gathering a synergistic combination of information from 
several fields and spanning many wavelengths. Conducting searches for biomarkers at infrared 
wavelengths is particularly convenient owing specifically to rovibrational C-H stretching 
modes in hydrocarbons, which fall in the range ~ 3.2 – 3.6 µm.  More generally, in the 2-5 
µm spectral region, many molecules of possible biological and geothermal origin have strong 
signatures, for example H2O, HDO, CO2, CH4, C2H6, H2CO, CH3OH, C2H2, C2H4, SO2, OCS, N2O, 
NH3, HCN and CH3Cl. 

We have investigated, both theoretically and by means of high-resolution spectroscopic 
observations, this rich spectral region in comets, planets, and protoplanetary disks. 
Increasingly sensitive studies of cometary and planetary atmospheres have become possible 
thanks to recent (and ongoing) technological developments in infrared instrumentation.  
Specifically, the cross-dispersed infrared echelle spectrometer at Keck II (NIRSPEC) has 
proven to be a particularly excellent tool because of its high resolving power and broad 
spectral coverage. In this talk, we will present synthetic spectra and observations of comet 
73P/Schwassmann-Wachmann 3 (in May 2006) and Mars (in January 2006), using NIRSPEC.

Taking both bodies to be proxies for different stages of our Solar System evolution (comet: 
pristine, Mars: evolved), we will compare their observed chemical signatures and will 
discuss how they relate to the different stages of solar system evolution (and, by 
extension, of potential extra-solar planetary system formation and evolution).