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SEARCH FOR COMPLEX ORGANIC MATTER AND SOUNDING OF EUROPA' SURFACE AND NEAR-SURFACE ATMOSPHERE BY MEANS OF FAR IR & TERAHERTZ SPECTROSCOPY
A.V.Rodin1,2, G.N. Goltsman3, N.A.Evdokimova1, M.V.Gerasimov1, I.I.Vinogradov1, and A.A.Fedorova1
1Space

Research Institute Institute of Physics and Technology Teaching University

2Moscow 3Moscow


: THz spectroscopy is a quickly developing area related to detection of organic matter. This spectral range corresponds to vibration modes of large molecules and intermolecular bonds in solids and liquids.

background

THz spectra of a sucrose crystal for different angles between its b-axis and THz polarization. From R. Rungsawang, Y. Ueno, I. Tomita, and K. Ajito, Opt. Express, 2006, 14, 5765., Fig. 2.

THz spectra of polypeptide powder of glycine, (Gly)n (n = 1 ­ 4). As the chain length increases, distinct and new absorption features were produced. From M. R. Kutteruf, C. M. Brown, L. K. Iwaki, M. B. Campbell, T. M. Korter, and E. J. Heilweil, Chem. Phys. Lett., 2003, 375, 337


Sustaining demand on commercial security equipment focused on complex organic species, along with biotech industry, drives dramatic boost in terahertz area for last 5 years Cheap and reliable sources and detectors to be brought to the market within few years
proposer's team has 20+year heritage of space instrument building


A far-IR & THz channel is proposed for TDLAS instrument Goals: search for organic matter of biogenic origin, comprehensive analysys of abiogenic organics (tholin-like polymers, PAHs etc), measurement of water spin-isomers. Method: (i) gas phase spectroscopy (ii) ice sample transmission spectroscopy (iii) reflection spectroscopy on selective adsorption filter Sensitivity ­ ppm level in raw ice sample
Wavelengths: (i) 7-12 m (ii) 15-25 m (iii) 70-90 m - search for simple organic volatiles (gas phase transmission) - search for condensed organics in filter (solid-state reflection) - search for condensed organics in ice; trapper ions; ice inner structure (solid-state transmission) - spin-isomer analysis of evaporated water ice (gas phase transmission)


Far-IR & THz passive sounding from Europa orbiter: Goals: (i) Surface and subsurface thermal structure (ii) Ice and regolith microphysical structure (iii) Search for traces of PAH, tholin and other organic matter on the surface Method ­ homodyne detection with He-cooled 80 nm-size antenna Sensitivity ­relative absorption at 10-8 level


Spectral properties of Europa' regolith in THz range
· · · · Discrete Dipole Approximation for near-field interactions Non-coherent radiative transfer for far-field Mixture of water ice and organics Fractal aggregates with variable monomer size

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Porous ice

Monomer radius: Black ­ 1 m Red ­ 7.5 m Green ­ 60 m Blue ­ 475 m

Volume extinction

Relative absorption


Surface thermal emission
Ice, T = 100 K, T = 0.2 K/cm Monomer radius: Black ­ 1 m Red ­ 7.5 m Green ­ 60 m Blue ­ 475 m


Naphthalene: a simple PAH
Relative absorption Monomer radius: Black ­ 1 m Red ­ 7.5 m Green ­ 60 m Blue ­ 475 m


Conclusions
· Far-IR and terahertz spectroscopy is an encouraging method for exploring Europa · The only remote method that allows to discriminate between common extraterrestrial organic matter from potential life markers · Experimental techniques allow for both remote and in vitro analyses · Quickly developing and demanded area of technology ­ hope for cheap and reliable solutions