Spectro-photometric signatures of abiotic and biotic complex organic matter
This CSH project aims to characterize in the laboratory the spectro-photometric signatures of biotic
and abiotic complex organic matter. It can be split in two sub-projects: (1) Abiotic organics on Solar
System surfaces: Our goal is to help the interpretation of remote sensing data from comets, icy
satellites, etc. by investigating the spectro-photometric properties of mixtures containing ice,
minerals and complex organics. (2) The search for surface biosignatures: 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.
Status of the project on 29.04.2015:
(1) Abiotic organics on Solar System surfaces:
Sublimation of icy surfaces: Following the campaign of laboratory experiments described in
the previous report, we have prepared two papers presenting the results of these experiments
and their implications for comets and icy planetary surfaces. The first paper, currently under
review in Icarus, shows the evolution of the structure/texture and of the visible and near-infrared
(VIS-NIR) spectral reflectance of surfaces made of water ice mixed with analogues of complex
extraterrestrial organic matter, named tholins, under low temperature (<-70°C) and pressure (105
mbar) conditions. The second paper, which will be submitted in May, extends this study to ices
containing silicates and organic matter. The influences of the concentration and of the way the
ice and the impurities are mixed together, either as intra-mixtures (inclusions of non-volatiles
within water ice grains) or inter-mixtures (non-volatiles deposited as a coating around pure
water ice grains) have also been investigated. The results highlight the different properties of the
residues obtained after sublimation in term of porosity, outburst-like events and reflectance. We
found that the mixture type and the presence of organics are the key parameters controlling the
internal coherence, and consequently the main properties of the residues (see Figure 1). This
work has contributed to the interpretation of remote sensing data obtained by the OSIRIS
camera onboard Rosetta, in two papers submitted to Astronomy & Astrophysics.
Simulation of Titan surface: The Huygens probe has returned VIS-NIR reflectance spectra of
the surface of Titan during its descent and landing on this moon of Saturn in January 2005. Since
then, no definitive interpretation has been proposed to explain the reflectance spectrum and the
scattering properties of the surface. In order to contribute to the interpretation of these data, we
have measured the phase curves and the reflectance spectra of mixtures of water ice with Titan
tholins. The first results of this study indicate that a porous matrix of Titan tholins wetted by
liquid hydrocarbons might explain at least several characteristics of the surface spectra observed
by Huygens. This work was presented in a poster at the EGU General Assembly 2015.
Figure 1: High resolution images of the surfaces of samples of water ice mixed with tholins after sublimation. (a) intramixture of 0.1% tholins and water ice particles of 67±31 μm, (b) inter-mixture of 0.1% tholins and pure water ice particles of
67±31 μm, (c) inter-mixture of 0.1% tholins and pure water ice particles of 4.5±2.5 μm. These images were taken in situ,
while the samples were sublimating inside the SCITEAS chamber. (Poch et al., submitted to Icarus)
(2) The search for surface biosignatures:
In collaboration with the Institute of Bacteriology and the Institute of Cell Biology, we have
performed several experiments relative to the photometric properties of surface samples
containing pigmented bacteria. Deinococcus Radiodurans bacteria were mixed with liquid water,
coarse sand, fine silicate, and water ice, and in each case their spectro-photometric properties
were measured (spectral reflectance and bidirectional reflectance). We are also investigating the
effects of biofilms of other pigmented bacteria on the reflectance. A paper presenting the results
of these measurements is currently in preparation for Astrobiology.
Up to now our measurements show that bacteria do not affect the phase curves, and
absorption bands alone cannot provide an unambiguous biosignature detection. The optical
activity displayed by some of the molecules of life, which are homochiral, could help to precise
the diagnostic made by remote sensing techniques. The polarization of the light, and specifically
the circular polarization, could be a marker of homochirality. Since the last report, we have
received the polarimeter capable of measuring the circular polarization of visible light. We are
currently testing and calibrating the device and we will perform our first measurements in the
coming weeks.
Papers related to this CSH project:
Poch, O., Pommerol, A., Jost, B., Carrasco, N., Szopa, C., Thomas, N., Sublimation of water ice mixed
with silicates and tholins: evolution of surface texture and reflectance spectra, with implications for
comets, in preparation for Icarus.
Poch, O., Pommerol, A., Jost, B., Carrasco, N., Szopa, C., Thomas, N., Sublimation of ice-tholins
mixtures: a morphological and spectro-photometric study, Icarus, submitted, 1 February 2015.
Papers including contributions from this CSH project:
N. Thomas, A.-T. Auger, B. Davidsson, M.R. El-Maarry, S. Fornasier, L. Giacomini, A.G. Gracia Berna,
S.F. Hviid, W.-H. Ip, L. Jorda, H.U. Keller, J. Knollenberg, E. Kührt, I.L. Lai, Y. Liao, R. Marschall, M.
Massironi, S. Mottola M. Pajola, O. Poch, A. Pommerol, F. Preusker, F. Scholten, C.C. Su, J.S. Wu, J.-B.
Vincent, H. Sierks, C. Barbieri, P.L. Lamy, R. Rodrigo, H. Rickman, D. Koschny, M. F. A’Hearn, M.A.
Barucci, J-L. Bertaux, I. Bertini, G. Cremonese, V. Da Deppo, S. Debei, M. Fulle, O. Groussin, P.J.
Gutierrez, J.-R. Kramm, M. Küppers, L. M. Lara, M. Lazzarin, J. J. Lopez Moreno, F. Marzari, H.
Michalik, G. Naletto, C. Güttler, and S. Marchi. Transport of particles across the nucleus of comet
67P/Churyumov-Gerasimenko, submitted to Astronomy & Astrophysics.
A. Pommerol, N. Thomas, M. R. Elmaarry, M. Pajola, O. Groussin, A. -T. Auger, N. Oklay, S. Fornasier,
B. Davidsson, A. Gracia, B. Jost, R. Marschall, O. Poch, M. A. Barucci, J. L. Bertaux, H. U. Keller, E.
Kuehrt, S. Mottola, G. Naletto, et al. OSIRIS observations of metre-size exposures of H2O ice at the
surface of 67P/Churyumov-Gerasimenko and comparison to laboratory experiments, submitted to
Astronomy & Astrophysics.
Jost, B., A. Pommerol, O. Poch, B. Gundlach, M. Leboeuf, M. Dadras, J. Blum, and N. Thomas,
Experimental characterization of the opposition surge in fine-grained water-ice and high albedo
analogs, Icarus, submitted, 10 August 2014.
Pommerol, A., Jost, B., Poch, O., Vuitel, B., Elmaarry, M. R., Thomas, N., (2015), The SCITEAS
experiment: laboratory studies of the sublimation of icy planetary analogues, Planetary and Space
Science 109-110, 106-122.
Posters presented at conferences, related to this CSH project:
O. Poch, B. Jost, A. Pommerol, N. Carrasco, C. Szopa, N. Thomas, Spectro-photometric properties of
mixtures of Titan tholins with water and hydrocarbon ices measured in the laboratory to support the
interpretation of Huygens DISR spectra, European Geosciences Union General Assembly 2015, 12-17
April 2015, Vienna, Austria
O. Poch, A. Pommerol, B. Jost, I. Roditi, J. Frey, N. Thomas, Laboratory insights into the detection of
surface biosignatures by remote-sensing techniques, Search for Life beyond the Solar System Exoplanets, Biosignatures & Instruments 2014, March 17-21, Tucson, Arizona, USA
O. Poch, Pommerol, A., Jost, B., Carrasco, N., Szopa, C., Roditi, I., Frey, J., Thomas, N., Spectrophotometric signatures of astrophysical surfaces containing abiotic or biotic organic molecules,
Colloquium of the French Society of Exobiology 2014, October 6-9, 2014, La Baule, France
A., Pommerol, N. Thomas, M.A. Barucci, J.L. Bertaux, B. Davidsson, M.R. El Maarry, F. LaForgia, S.
Fornasier, A. Gracia, O. Groussin, B. Jost, R. Marschall, G. Naletto, N. Oklay, M. Pajola, O. Poch, and
the OSIRIS Team, Metre-size bright spots at the surface of comet 67P/Churyumov-Gerasimenko:
Interpretation of OSIRIS data using laboratory experiments, European Geosciences Union General
Assembly 2015, 12-17 April 2015, Vienna, Austria
B. Jost, A. Pommerol, O. Poch, M. R. El-Maarry, N. Thomas, The LOSSy laboratory for spectrophotometric characterization of cometary and planetary analogues at University of Bern, European
Planetary Science Congress 2014, 7-12 September 2014, Cascais, Portugal
B. Jost, A. Pommerol, O.Poch, B. Gundlach, N. Thomas, Low phase angle photometry of ice in the
laboratory and implications for the surface of icy satellites, European Planetary Science Congress
2014, 7-12 September 2014, Cascais, Portugal
A. Pommerol, N. Thomas, B. Jost, O. Poch, Photometric study of cometary analogs in the LOSSy
laboratory at the University of Bern, Asteroids, Comets and Meteors conference 2014, 30 June - 4 July
2014, Helsinki, Finland