Spectro-photometric signatures of abiotic and biotic complex organic matter
Final report on the project on 09.12.2015
1. Scientific contribution
a. Theme 1: Abiotic organics on Solar System surfaces
b. Theme 2: The search for surface biosignatures
c. Peer-reviewed publications
d. Oral presentations
e. Poster presentations
2. Outreach contribution
1. Scientific contribution
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.
a. Theme 1: Abiotic organics on Solar System surfaces
Sublimation of icy surfaces: First, we have extended the existing methods of production of
icy samples in the laboratory of Bern. New reproducible methods of production, mixing and
characterization have been developed. Armed with that, we have performed a campaign of
laboratory experiments aiming at studying the temporal evolution of sublimation lag deposits
formed from cometary ice mixture analogs exposed to low temperature and pressure conditions
similar to those found on a cometary or icy planetary surface. The first results, currently in press
in Icarus, shows the evolution of the structure/texture and of the visible and near-infrared (VISNIR) 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. In a second paper, currently under review in Icarus, we extend 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
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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 published in Astronomy & Astrophysics. They are also of
interest for other Rosetta instruments, GIADA or COSIMA for example.
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., in press in Icarus)
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.
b. Theme 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). A paper presenting the
results of these measurements is currently under review in Astrobiology.
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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. In order to perform this
measurement, we have developed a new setup in the laboratory of Bern, including a high
precision Stokes polarimeter. This setup can currently measure the polarization of surface
samples at 3 wavelengths in the visible range and from about 3 to 30° phase angles. Calibration
and first measurements of abiotic and biotic samples, including icy samples, are ongoing on this
setup. The measurement of a signal specific to biology will probably require a higher spectral
resolution, but the current setup is of high interest to support polarimetric astronomical
observations. The development of this facility, initiated by this project, is continuing within the
NCCR Planet S in collaboration with astronomers from ETH Zurich.
Reflectance d’un microorganisme pigmenté
1
Deinococcus radiodurans...
...pure
(hydrated)
(dehydrated)
 pigment toujours visible
 NIR dominé par l’eau
...with silicates
 absorptions électroniques
des minéraux masquent le
pigment
...in liquid water
...in water ice particles
 pigment visible
 NIR saturé par eau
 la réflectance élevée de
l’eau et son absence
d’absorption dans le visible
favorisent la détection des
pigments
 bandes NIR masquées par
l’eau
Poch et al. (under review in Astrobiology)
Figure 2: Reflectance spectra of Deinococcus radiodurans in various surface media.
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c. Publications 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, under review in Icarus
Poch, O., Pommerol, A., Jost, B., Frey, J., Roditi, I., Thomas, N., Remote sensing of potential
biosignatures from rocky, liquid or icy (exo)planetary surfaces, under review in Astrobiology
Poch, O., Pommerol, A., Jost, B., Carrasco, N., Szopa, C., Thomas, N., Sublimation of ice-tholins
mixtures: a morphological and spectro-photometric study, Icarus, in press
d. Publications including contributions from this CSH project:
Yoldi, Z., A. Pommerol, B. Jost, O. Poch, J. Gouman, and N. Thomas, VIS-NIR reflectance of water
ice/regolith analogue mixtures and implications for the detectability of ice mixed within planetary
regoliths, Geophysical Research Letters 42, 6205–6212.
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, Astronomy & Astrophysics 583, A17.
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, Astronomy &
Astrophysics 583, A25.
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 264, 109-131.
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.
e. Oral presentations relative to this CSH project
O. Poch, J. Frey, I. Roditi, A. Pommerol, B. Jost, N. Thomas, Détection à distance de biosignatures à la
surface de planètes habitables, Exobiologie Jeunes Chercheurs EJC’15, 16-18 novembre 2015, CNES,
Paris
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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
O. Poch, N. Thomas, I. Roditi, J. Frey, A. Pommerol, Spectro-photometric signatures of astrophysical
surfaces containing abiotic or biotic organic molecules, Space Research & Planetary Sciences Division
Seminar on Planetary Sciences, 15 October 2014, University of Bern
O. Poch, N. Thomas, I. Roditi, J. Frey, A. Pommerol, Spectro-photometric signatures of astrophysical
surfaces containing abiotic or biotic organic molecules, Kiepenheuer-Institut fuer Sonnenphysik (KIS)
Astrophysical Colloquium, 13 November 2014, Freiburg
f.
Posters presented at conferences, related to this CSH project
A. Pommerol, O. Poch, B. Jost, Z. Yoldi, N. Carrasco, C. Szopa, N. Thomas, Sublimation of Ices
Containing Organics and/or Minerals and Implications for Icy Bodies Surface Structure and Spectral
Properties, American Geophysical Union Fall Meeting, 15-19 December 2015, San Francisco, USA
O. Poch, A. Pommerol, B. Jost, J. Frey, I. Roditi, and N. Thomas, Remote sensing of potential
biosignatures from rocky, liquid or icy surfaces, Pathways Towards Habitable Planets II, 13-17 July
2015, Bern, Switzerland
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
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
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2. Outreach activity
We have developed a scientific activity for children entitled “Ausserirdische Zellen dank ihrer
Atmung entdecken” during the “Planetenjagd” on 5 September 2015. During this activity, the
children were invited to perform a biochemistry experiment demonstrating the production of carbon
dioxide gas by humans and by yeasts. This experiment shows that life forms produce gases and
demonstrate that to search for life elsewhere we can search for gases produced by life. The material,
posters and protocol necessary to perform this experiment has been prepared and can be used again
for future public events.
Figure 3: On Saturday, September 5th, roughly 400 visitors of all ages embarked on a search for habitable planets. During
the event at the «Center for Space and Habitability» CSH, both young and old engaged in a discussion about the origin of
life and talked about potential life beyond Earth. During the workshops, the participants tinkered paper models of the
Rosetta spacecraft and the CHEOPS space telescope, examined with balloons and lime water if yeast emits CO2 as we do,
and made their own mini-comets. (from Unibe Facebook page)
https://www.facebook.com/media/set/?set=a.869411759778845.1073741912.150609974992364&type=3
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