Diapositiva 1 - IDEALS

Diapositiva 1 - IDEALS

Stability of extraterrestrial glycine under energetic particle radiation estimated from 2 keV electron bombardment experiments. Beln Mat, Isabel Tanarro, Rafael Escribano, Miguel A. Moreno Vctor J. Herrero Instituto de Estructura de la Materia IEM-CSIC, Madrid INSTITUTO DE ESTRUCTURA [email protected] DE LA MATERIA ISMS - 70TH MEETING - JUNE 22-26, 2015 - CHAMPAIGN-URBANA, ILLINOIS glycine Detected in our Solar System Comets Meteorites The Deep Impact probe Image: NASA/JPLCaltech/UMD Murchinson meteorite: 20 aminoacids detected glycine the most abundant Not detected in the Interstellar Medium However other organic molecules of similar complexity have been found

NH2-CH2-COOH HCOOCH3 HOCH2CH2OH CH3CHO glycine In the laboratory Synthesized by UV irradiation of ice analogues containing H2O, NH3, CO2, CO, CnH2n+2 It can be formed in the conditions available in interstellar ice mantles Could glycine have been delivered to planets by meteorites and comets, and thus be the seed of life? Could glycine resist the radiation field in space? Laboratory studies indicate that glycine would be destroyed by UV irradiation in the diffuse ISM and in unshielded surfaces within the Solar System In dense molecular clouds or in the subsurface of Solar System bodies the external photon flux decreases rapidly, but glycine can still be destroyed by cosmic rays We are going to use 2 keV electrons to simulate the effect of cosmic rays on extraterrestrial glycine EXPERIMENTAL SETUP High vacuum chamber: 10-8 mbar Closed cycle He cryostat. 14 - 300K

Vertex 70 Bruker FTIR spectrometer. Normal incidence transmission. Sublimation mini-oven Electron gun Schematic view of the chamber glycine oven electron gun 2 keV electron flux : 8 1011 cm-2 s-1 a b s o rb a n c e Infrared spectra of vapor deposited glycine crystal 0.6 crystalline 300 K 300 K 0.4 0.2 zwiterionic -

neutral amorphous-zw 20 K 90 K 0.2 0.0 a b s o rb a n c e + a b s o rb a n c e 0.0 amorphous-(zw+ne) 20 K 20 K 0.08 0.04 0.00 3500 3000 2500

2000 1500 -1 wavenumber cm 1000 absorbance 0.04 (a) 300 K 15 min 41 min 0 min 6 min absorbance 90 5 nm layers 0.02 b -glycine at 300K 0.00 0.04 (b) 90 K 54 min 82 min 0 min

20 min 0.02 amorphous glycine at 40 K 0.00 (c) 40 K absorbance GLYCINE PROCESING by 2 keV electrons 0.04 42 min 72 min 117 min 0 min 20 min 0.02 amorphous glycine at 90 K 0.00 2400 2200 2000 1800 1600 1400 1200 1000 800 -1 wavenumber (cm ) Normalized intensity decay of the 1405 cm-1 band of glycine, in logarithmic scale, as a function of fluence We assumed a single forward first order reaction.

0.0 90 K, 90 nm 90 K, 35 nm 40 K, 80 nm 20 K, 84 nm -0.5 -1.0 ln(I / I0) -1.5 ln -2.0 -2.5 -3.0 -3.5 50 100 150 200 250 2 F(electrons/cm ) F = Fluence = Flux (electrons cm-2 s-1 ) time (s)

B. Mat et al., 2015, ApJ 806:151 ( ) s: destruction cross section (cm2) 300 K, 90 nm 0 I = F I0 300 T(K) s (10-16 cm2) 300 17.6 1 90 9.1 1 Comparison with Gerakines et al., Icarus (2012) Amorphous glycine processed with 0.8 MeV protons 900 nm H+ 0.8 MeV e- 2 keV

secondary electrons 90 nm Linear energy transfer (H+) 44.8 keV/mm Linear energy transfer (e-) 22 keV/mm Radiolisis yield G (molec/100eV) protons 14 K keV e- and MeV H+ produce similar effects when the irradiation reaches the whole sample 5.8 0.5 electrons 20K 5.6 0.6 irradiation with e- appropriate to simulate cosmic rays half-life dose D1/2 the energy required to reduce the initial concentration to 50% Location Dense ISM

T (K) 10 Radiation dose rate Glycine Half-life (eV/molec/year) (year) 1.6 x 10-7 1.6 x 107 In dense ISM the amino acid could have a chance to survive until the protostellar phase and then be incorporated to the material of the resulting protoplanetary disk. Irradiation products at low temperature absorbance 0.06 (a) 0.03 0.00 90 K 40 K 40 K 2400

2200 2000 1800 1600 1400 1200 -1 wavenumber (cm ) absorbance 0.02 experimental 5 Gaussians sum (b) carrier Band center, cm-1 CO2 2340 OCN- 2164

CO 2136 CN- 2077 Amide I 1673.3 Amide II 1573.4 Deform., scissor -CH3, -CH2 1480.9 Stretching, -RCO2- 1405.2 Amide III 1319.0 90 K 0.01 0.00 1800 1600

1400 -1 wavenumber (cm ) 1200 The tentative assignment of amide bands suggests that the irradiation process leads to the formation of polypeptides. summary and conclusions The effect of 2 keV electron irradiation is confirmed to be similar to that of MeV protons for samples with thickness below the penetration depth of the electrons. With the lifetimes estimated in the present work there is a slim chance, that hypothetical interstellar glycine might have survived the passage from the pre-solar dense molecular cloud to the present Solar System. INSTITUTO DE ESTRUCTURA DE LA MATERIA

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