HR: 0800h
AN: P41C-03    [Abstracts]
TI: Oxygen and Carbon Isotope Ratios in CO₂on Mars
AU: * Krasnopolsky, V A
EM: vkrasn@verizon.net
AF: Department of Physics, Catholic University of America, 620 Michigan Avenue, N.E., Washington, DC 20064, United States
AU: Maillard, J
EM: maillard@iap.fr
AF: Institute d'Astrophysique de Paris, 98 bis Blvd. Arago, Paris, 75014, France
AU: Owen, T C
EM: owen@ifa.hawaii.edu
AF: Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, United States
AU: Toth, R A
EM: Robert.Toth@jpl.nasa.gov
AF: JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AU: Smith, M D
EM: Michael.D.Smith@nasa.gov
AF: NASA GSFC, Code 693, Greenbelt, MD 20771, United States
AB: The major problems in spectroscopic determinations of the oxygen and carbon isotope ratios on Mars are uncertainties associated with (1) equivalent widths of the observed absorption lines, (2) line strengths in spectroscopic databases, and (3) thermal structure of the Martian atmosphere during the observation. We have made special efforts to reduce all these uncertainties. We observed Mars using Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope. While the previous measurements of the oxygen and carbon isotope ratios on Mars were byproducts in observations of other species, our observation was specifically aimed at the isotope ratios. The observation covered a range of 6020 to 6310 cm^-1 with the highest resolving power of 400,000 and a signal-to-noise ratio of 180 in the middle of the spectrum. The chosen spectral range involves 512 lines of the main isotope, 197 lines of ¹³CO₂, 184 lines of CO¹⁸O, and 120 lines of CO¹⁷O. (Lines with strengths exceeding 10^-27 cm at 220 K are considered here.) Due to the high spectral resolution, most of the lines are not blended. Uncertainties of retrieved isotope abundances are in inverse proportion to resolving power, signal-to-noise ratio, and square root of the number of lines. One of us (R.A. Toth) is making laboratory studies of the CO₂isotope line strengths in the range of our observation. This work is aimed to achieve an accuracy of ~1% in the line strengths. Detailed observations of temperature profiles and dust abundances using MGS/TES are used to simulate each absorption line at various heights in each part of the instrument field of view and then sum up the results. Thermal radiation of Mars' surface and atmosphere is negligible in the chosen spectral range, and this reduces errors associated with uncertainties in the thermal structure on Mars. Using a combination of all these factors, we plan to achieve the highest accuracy in measuring the CO₂isotope ratios. The results will be reported.
DE: 0343 Planetary atmospheres (5210, 5405, 5704)
DE: 5405 Atmospheres (0343, 1060)
DE: 5410 Composition (1060, 3672)
DE: 5455 Origin and evolution
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly