2010 Annual Science Report
University of Wisconsin Reporting | SEP 2009 – AUG 2010
Project 1A: Stability of Polycyclic Aromatic Hydrocarbons and Fullerenes in Space Environment
EXPOSE-R is a multi-user facility attached to an external platform at the outer hull of the Service Module of the International Space Station (ISS). The external platform, called URM-D is part of the Russian Segment. EXPOSE-R accommodates 10 biological and biochemical experiments, which are mounted in three removable containers, called trays. The Organics experiment on EXPOSE-R consists of thin films of polycyclic aromatic hydrocarbons (PAHs) and fullerenes that are exposed ~18-24 months to solar UV under vacuum or controlled atmosphere. The samples of the Organics experiment were analyzed before exposure to space environment with UV, visible and infrared spectroscopy and the ground control samples are measured regularly in the laboratory. EXPOSE-R experiments were activated by Extra Vehicular Activity (EVA) in March 2009 and are currently in orbit. The trays will be recovered by EVA again, brought into the RS-ISS and returned to Earth by the manned SOYUZ return capsule in early spring 2011.
The Organics experiment will monitor the chemical evolution, survival, destruction and chemical modification of PAHs, fullerenes and macromolecules in space environment. From the results we shall determine constraints on the photochemistry of these compounds in the interstellar medium. The radiation dose that is collected by the samples during flight exceeds the limits of simulations in the laboratory and the results will greatly enhance our knowledge on the evolution of large molecules in space environments. Samples are deposited in thin films by sublimation on MgF2 windows inside the sample cell. Dark samples are shielded from the UV photons and enable us to discriminate between the effects of exposure to photons and cosmic rays. PAHs are highly abundant and ubiquitous compounds in the interstellar medium. Fullerenes C60 and C70 have recently been confirmed in the hydrogen-poor planetary nebula Tc-1. Among the exposed species are C60, C70, coronene (C24H12), ovalene (C32H14), dicoronylene (C48H20), and others.
1) Ground-based monitoring of EXPOSE-R samples in simulated space environment:
The Ocean Optics HR4000 spectrometer with a fiber optic interface has been used to record the transmission/absorption spectra of the ground witness EXPOSE-R Organics sample cells. This spectrometer shares many of the optical design features, as well as much of the software, with the O/OREOS (Organism/Organic Exposure to Orbital Stresses) flight spectrometer scheduled for launch in Fall 2010. Through the implementation of the high-precision x-y-z slide assembly (Velmex) in May 2009, it has allowed for positioning the sample carrier relative to the spectrometer input with high accuracy. Transmission/absorption spectra were recorded for the 16 sample cells in the closed-bottom ground witness sample carrier of the EXPOSE-R Organics experiment every 3-4 months over 18 months. The measurements confirm that no alterations have occurred in the spectra of the ground sample carriers (Fig. 1). The preliminary measurements and studies were reported at the ACS 239th Conference, the AAS 216th Conference, and the Astrobiology Science Conference 2010. In addition a publication is in preparation for Advances in Space Research.
2) Development of a laboratory prototype UV-Visible spectrometer for in-situ measurements of organic materials on future free-flyers and lunar surface exposure facilities
In addition to the measurements on the EXPOSE-R samples, preliminary spectra of sample materials were collected that will be exposed on the O/OREOS Nanosatellite mission mentioned above, using the Ocean Optics HR 4000 spectrometer. These samples included thin films of anthrarufin, iron tetraphenylporphyrin chloride, isoviolanthrene, and tryptophan. The spectroscopic information helped to optimize the final film thicknesses of samples to be flown on O/OREOS. The preflight O/OREOS sample transmission/absorption spectra were recorded and monitored once per month for any sample degradation/changes. A comparison of data from the EXPOSE-R Organics experiment and the O/OREOS experiment were reported at the PAHs and the Universe symposium 2010.