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2007 Annual Science Report

NASA Goddard Space Flight Center Reporting  |  JUL 2006 – JUN 2007

Cosmic Ice Laboratory

Project Summary

In the Cosmic Ice Laboratory we simulate the low-pressure, low-temperature environment of space using a high-vacuum chamber and a cryostat. Ice samples are prepared on a pre-cooled mirror inside the cryostat and then exposed to energetic processing.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

In the Cosmic Ice Laboratory we simulate the low-pressure, low-temperature environment of space using a high-vacuum chamber and a cryostat. Ice samples are prepared on a pre-cooled mirror inside the cryostat and then exposed to energetic processing. They can be irradiated with 1-MeV protons to simulate cosmic-ray bombardment, photolyzed to simulate vacuum-ultraviolet (UV) exposure, or irradiated with 10-keV electrons to simulate a variety of magnetospheric and circumstellar environments. Our work this past year focused on the radiation chemistries of nitrile and water-nitrile ices, the amino acids valine and isovaline, and on H2O-rich ices containing O2. These studies were motivated by IR observations of acetonitrile (CH3CN) in Titan’s atmosphere, cometary comae, and interstellar regions, by the chemical analysis and identification of isovaline in meteorites, and by UV observations of O2 in H2O-rich ices on Europa. In each case, the material we investigated was the same as that found in a specific low-temperature space radiation environment.

A major study to unravel the solid-phase radiation chemistry of nitrile and water-nitrile ices was completed during the past year. Zack Posun (GCA 2006 intern) performed laboratory experiments that showed unequivocally that HCN is a radiation product of CH3CN, by using isotopically-labeled starting materials, and that the cyano (C∫N) group is radiolytically oxidized in H2O-ice to form the cyanate ion (OCN) which in turn is converted into CO2 by further oxidation. Spectra of isotopically-labeled ketenimine, H2C2NH, also were obtained, supporting this molecule’s earlier identification in Hudson and Moore (Icarus 2004, 172, 466) and our prediction that it is an interstellar species. Ketenimine’s recent discovery in the star-forming region Sagittarius B2(N) by Lovas et al. (Ap. J. 2006, 645, L137) attests to the predictive power of this experimental approach. Building on our previous work, we have continued to examine organic refractory residues from irradiated nitriles. Analyses done in conjunction with Dr. Jason Dworkin (GCA) revealed a suite of amino acid precursors. Figure 1 is taken from a manuscript describing these experiments, which has been submitted for publication.
A study of the formation, destruction, racemization, and thermal stability of the amino acids isovaline and valine has been initiated. Isovaline is of astrobiological interest since its enantiomers were found in CM carbonaceous chondritic meteorites (e.g., Murchison and Murray) in apparently equal ratio (racemic form) and in higher abundance than glycine (the simplest amino acid). Meteoritic isovaline, which is not biologically-active, is thought to have an abiotic origin. Initial proton irradiations of D- and L-valine at 10 K (Figure 2) showed that about half of the target molecules were destroyed with a dose of ~1 eV molecule_1, corresponding to a half-life of ~3 _ 106 years in dense-cloud environments. Chemical analyses of the post-radiation residues showed that racemization had occurred, but not isomerization. Ariel Lewis (GCA 2007 intern) helped with our continuing study of the low-temperature radiolytic syntheses of valine and isovaline from iso- and sec-butylamine in the presence of CO2.

In an exciting new result, Paul Cooper (NPP Fellow) obtained direct IR evidence for O-atom production during irradiation of frozen H2O-rich mixtures containing O2. Cooper identified 16O-containing ozone isotopologues in irradiated H216O + 18O2 ices. The ozone variants found are 666O3, 668O3, 686O3, 886O3, and 888O3 (666O3 is 16O16O16O, 668O3 is 16O16O18O, etc.). Figure 3 shows the growth of the relevant absorptions in the 10-mm (wavelength) region as a function of radiation dose. These observations support the idea that O2 detected on Europa’s surface, for example, is produced by the radiation-induced chemical decomposition of H2O into H2 molecules and O atoms. Photolytic production of O from gas-phase H2O is well known, but the corresponding process had not been identified in condensed-phase water, until now.

New proposal funded for astrobiology-motivated research

  • MFRP, 2007 – 2010: A Laboratory Study of the Stability of Acids Relevant to Mars
  • Other activities, including outreach, during the past year

  • Initial testing of 10-keV electron gun completed
  • Organized two AGU meeting sessions
  • Attended ACS, AGU, and DPS meetings and made presentations at each
  • Presented invited talks at the Radiation Research Society’s annual meeting in Philadelphia and at an international workshop on “Trans-Neptunian Objects: Dynamical and Physical Properties” in Italy
  • Web site for the Cosmic Ice Laboratory maintained and improved
  • One astrobiology course taught to undergraduates (fall, 2006)
  • Facilitated public viewing sessions at a local observatory
  • Reviews

    These are an indication of our continued involvement in a variety of astrobiologically-related efforts and of our standing in the professional community.

    Reviewed fifteen manuscripts for publication (Astrobiology, Origin of Life and the Evolution of the Biosphere, Astrophysical Journal, Astronomy & Astrophysics, Icarus, Journal of Physical Chemistry, Chemical Physics, Chemical Physics Letters, Journal of Chemical Education, and American Mineralogist)

    On-site reviewer for research proposals submitted to a NASA panel

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      Marla Moore
      Reggie Hudson

      Objective 2.2
      Outer Solar System exploration

      Objective 3.1
      Sources of prebiotic materials and catalysts

      Objective 7.1
      Biosignatures to be sought in Solar System materials