Spectro-photometric signatures of abiotic and biotic complex organic matter
Carbon is the fourth most abundant atom in the universe, and carbonaceous molecules, also called
organic molecules, are widespread from the interstellar medium to the surfaces of planets. Some of
these molecules constitute the building blocks shared by all life forms on Earth, and are dubbed
“biotic” organic molecules. Understanding the origin, distribution and evolution of organic matter
could help to figure out the emergence of life on Earth, and to search for other forms of life
elsewhere.
Remote sensing of planetary surfaces at visible and infrared wavelengths is the first source of
information we can get to infer the presence of organic molecules and potential habitats. Thus,
remote sensing techniques can serve as precursor for the identification of abiotic or biotic organic
matter located on planetary surfaces. In our Solar System, several objects are globally or locally
covered by organics, from icy satellites to comets. For these, remote sensing of the surface is a
requirement to identify and characterize landing sites of interest, prior to in situ analyses. Concerning
the characterization of exoplanets, for which lander missions are improbable, only a thoughtful
analysis of the light reflected by exo-atmospheres and surfaces will be possible to infer the presence
of organics, and ultimately of life.
In this context, this project aims to characterize in the laboratory the spectro-photometric signatures
of biotic and abiotic complex organic matter. Our goal is to help the interpretation of remote sensing
data from comets, icy satellites, Mercury etc. by investigating the spectro-photometric properties of
mixtures containing ice, minerals and complex organics. We also want to assess the potential of
optical remote-sensing methods to detect living organisms at the surface of Solar System objects and
exoplanets. How could we discriminate between abiotic and biotic surface organics via remote
sensing techniques? What could be a reliable surface biosignature in the light reflected by an
exoplanetary surface?
This laboratory work is conducted using equipment that has been developed for several years at the
Physics Institute of University of Bern for surface photometry studies (Pommerol et al., 2011). The
reflectance spectra and bidirectional reflectance function of dusty ice samples or soils containing
bacteria can be characterized in various environmental conditions. The experiments involving simple
living organisms are conducted in collaboration with the Institute for Cell Biology and the Institute for
Veterinary-Bacteriology of the University of Bern. During the project, the existing laboratory
equipment will be modified to incorporate polarization measurements, and particularly circular
polarization, because it can be a marker of homochirality, which is supposed to be a universal
property of life. Finally, the analyses of both biotic and abiotic materials will help to assess if, or in
which peculiar conditions, remote sensing techniques can discriminate between false positive and
strong biomarkers.
Ultimately, the obtained laboratory data could serve as reference data to guide and interpret future
observations, paving the way for the detection of life on distant exoplanets.
Pommerol et al. (2011), Photometry and bulk physical properties of Solar System surface icy analogs:
the Planetary Ice Lab oratory at University of Bern, Planetary and Space Science 59, 1601