Belén Maté, Isabel Tanarro, Rafael Escribano, Miguel A. Moreno Víctor J. Herrero Instituto de Estructura de la Materia IEM-CSIC, Madrid Stability of extraterrestrial glycine under energetic particle radiation estimated from 2 keV electron bombardment experiments. INSTITUTO DE ESTRUCTURA DE LA MATERIA ISMS - 70TH MEETING - JUNE 22-26, CHAMPAIGN-URBANA, ILLINOIS

The Deep Impact probe Image: NASA/JPL- Caltech/UMD Murchinson meteorite: 20 aminoacids detected glycine the most abundant glycine Comets Meteorites Detected in our Solar System Not detected in the Interstellar Medium NH 2 -CH 2 -COOH However other organic molecules of similar complexity have been found HOCH 2 CH 2 OH HCOOCH 3 CH 3 CHO

Synthesized by UV irradiation of ice analogues containing H 2 O, NH 3, CO 2, CO, C n H 2n+2 glycine In the laboratory 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: mbar Closed cycle He cryostat K Vertex 70 Bruker FTIR spectrometer. Normal incidence transmission. Sublimation mini-oven Electron gun

Schematic view of the chamber electron gun 2 keV electron flux : 8  cm -2 s -1 glycine oven

Infrared spectra of vapor deposited glycine + - crystalline amorphous-zw amorphous-(zw+ne) 300 K 90 K 20 K crystal zwiterionic neutral

GLYCINE PROCESING by 2 keV electrons 90 ± 5 nm layers  -glycine at 300K amorphous glycine at 90 K amorphous glycine at 40 K

F = Fluence = Flux (electrons cm -2 s -1 ) × time (s) 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.  : destruction cross section (cm 2 ) T(K)  ( cm 2 ) ± ± 1 B. Maté et al., 2015, ApJ 806:151

Comparison with Gerakines et al., Icarus (2012) Amorphous glycine processed with 0.8 MeV protons Linear energy transfer (H + ) 44.8 keV/  m Linear energy transfer (e-) 22 keV/  m e-e- 2 keV 90 nm H+H+ 0.8 MeV 900 nm secondary electrons Radiolisis yield G (molec/100eV) protonselectrons 14 K5.8 ± 0.520K 5.6 ± 0.6 irradiation with e- appropriate to simulate cosmic rays keV e - and MeV H + produce similar effects when the irradiation reaches the whole sample

half-life dose D 1/2 the energy required to reduce the initial concentration to 50% LocationT (K) Radiation dose rate (eV/molec/year) Glycine Half-life (year) Dense ISM x x 10 7 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.

carrierBand center, cm -1 CO OCN CO2136 CN Amide I Amide II Deform., scissor -CH 3, -CH Stretching, -RCO Amide III Irradiation products at low temperature 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