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Project Progress

In the Cosmic Ice Laboratory we simulate the vacuum and low-temperature environment of space using a high-vacuum chamber and a cryostat. Ice samples condensed on a cooled mirror inside the cryostat are irradiated with 1 MeV protons to simulate cosmic-ray bombardment or are photolyzed to simulate vacuum-ultraviolet (UV) exposure. Our progress this year focused on the radiation chemistries of acetonitrile and of H₂O-rich ices containing O₂. Both of these studies were motivated by IR observations: acetonitrile (CH₃CN) because of its detection in Titan, comets, interstellar regions, and H2O-rich ices containing O₂ because they represent the icy surface of Europa. In each case, the location observed is at low temperature and contains material exposed to a radiation environment.

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New results related to acetonitrile studies are that amino acids are detected in hydrolyzed residues from irradiated ¹³C-labeled CH₃CN ices. Jason Dworkin analyzed residues in the Astrobiology Analytical Laboratory using HPLC, GC, and MS methods. Figure 1 shows that the same fluorescene signals were detected for pure CH₃CN and CH₃CN diluted in H₂O-ice. The amino acids were identified by mass spectrometry of eluted material. Figure 2 shows the identification of D- and L-aspartic acid, glycine, βalanine, D and L-alanine, γABA, and D and L-β-ABA. The relative concentrations of amino acids in this residue resemble those found in CI meteorites such as Orgueil. Continued work to understand the chemistry of these and other important biomolecules is in progress.

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Exciting results related to frozen H₂₂ are that two new radicals have been identified in irradiated ices, and their formation and stability near 80 K show that similar species are relevant to the surfaces of Europa, Ganymede, and Callisto. Results of radiation experiments at 10 K using either ¹⁶O₂ or ¹⁸O₂ in H₂O-ice are compared in Figure 3 with the unirradiated H2O + O2 ice’s spectrum. Products are O₃, HO₃, and HO₂ (also H₂O₂, not shown). HO₂ and HO₃ have been overlooked by astrochemists and planetary scientists, but definitely contribute to the inventory of oxidants on Europa. These species have the ability to oxidize organics and perhaps destroy biomolecules. On the other hand, they may provide a source of chemical energy needed to sustain microbial life. Including these species in analyses relevant to the icy Galilean satellites will improve the accuracy of the chemical models.

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Outreach, facilities, and web page highlights from the past year are:

• One astrobiology courses taught to undergraduates (fall, 2005)
• Web site for the Cosmic Ice Laboratory maintained and improved
• 10 keV electron gun purchased with astrobiology funding has been received
• Presentation to the Florida Association of Physics Teachers
• Organized two meeting sessions (AOGS and AGU)
• Attended AbSciCon, ACS, AGU, AOGS, IAU, and DPS meetings and made presentations at each