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Overview on the study of astrophysical ices under ionizing radiation

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Involved people : Philippe Boduch, Alicja Domaracka , Hermann Rothard, Basile Augé, Gabriel Muniz-Vignoli, Aditya Agnihotri

Contracts : ANR IGLIAS (2013-2017), CAPES- COFECUB, BIORAD

Artist’s view of JUICE, the JUpiter ICy moons Explorer mission, in the Jovian system. credits : ESA/AOES.

A fruitfull collaboration between physicists of different community (ion-matter interaction and astrophysics) including two French laboratories (CIMAP and IAS) and two brazilian universities concerns the effects induced by heavy ion irradiation on astrophysical ices. Heavy ions (C, O, S, Fe, Ni) are present in the solar wind, in cosmic rays and in the magnetosphere of giant planets. Ices exist on many objects in space (icy mantles of dust grains in dense cloud, satellites of giant planets, comets, etc). The ices are formed mainly by simple molecules (like H2O, CO, CO2, NH3 ... ). In the laboratory, the icy samples are deposited and irradiated with swift heavy ions at low temperature (typically 15K-150K). In situ Fourier Transform Infrared absorption spectroscopy FTIR in the range 500-5000 cm-1 allows to observe the disappearance of molecules (fragmentation or sputtering), and the appearance of new molecular species as a function of the projectile fluence.

This latter topic, in the case of mixture gas ice sample is related to the question of the complex organic molecule production and the initial conditions for the emergence of life. We also obtained results on water ice structural modifications (amorphization and compaction). In particular we have demonstrated that cosmic rays are efficient enough to remove porosity from water ice.

Concerning Jovian moons, our work on water ice irradiation with sulphur ions proved that sulfur implantation strongly supports an exogenic origin of sulphuric acid on Europa. Finally, we started studying the irradiation of carbonaceous substrates covered with an icy mantle in order to characterise the production of new molecules at the interface.

For further details :

IR spectra of water ice before and after implantation of carbon (left panel) and sulfur (right panel) ions.
refs :
X. Y. Lv and al, Astrono. & Astrophys. 546 (2012) A81
J. J. Ding and al, Icarus 226 (2013) 860–864
X.Y. Lv and al, MNRAS 438 (2014) 922-929