f //11/// NASA-CR-198036 FINAL TECHNICAL REPORT INFRARED SPECTROSCOPY OF JUPITER AND SATURN NAGW #2194 Roger F. Knacke Division of Science Penn State Erie Station Road Erie, PA 16563-0203 Phone: (814) 898-6105 FAX: (814) 898-6213 [email protected] (NASA-CR-191034) INFRARED N95-24239 SPECTRQSCCPY OF JUPITER AND SATURN Final Technical Report (Pennsylvania State Univ.) 3 p Uncl as G3/?l 0045309 Strategy Infrared spectroscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn -- and of Titan, the enigmatic satellite of Saturn. The 5 micron spectral region of these objects is transparent to deep levels, and is therefore particularly useful for the identification of molecules in the deep atmosphere at very low (parts per billion) concentrations. In Titan, 5 micron observations probe atmospheric layers at or near the surface. The observations support and complement VOYAGER and CASSINI measurements. Ground-based spectroscopy is sensitive to lower mixing ratios for selected molecules, while the spacecraft mass and infrared spectrometers probe molecules that are inaccessible from the ground. The ground-based observations also provide time-based data for preparation for the CASSINI mission. Accomplishments In 1991 we obtained data at J, H, K, and M and made repeated observations of Titan's albedo as the satellite orbited Saturn. The J albedo is 12+-3% greater than the albedo measured in 1979; the H and K albedos are the same. There was no evidence for variations at any wavelength over the eastern half of Titan's orbit. We also obtained low resolution (R = 50) spectra of Titan between 3.1 and 5. t microns. The spectra contain evidence for CO and CH3D absorptions. Spectra of Callisto and Ganymede in the 4.5 micron spectral region are featureless and give albedos of 0.08 and 0.04 respectively. If Titan's atmosphere is transparent near 5 microns, its surthce albedo there is similar to Callisto's. These results were summarized in two papers by Noll and Knacke (1992, 1993; Appendix). In 1992 and 1993 we obtained further spectroscopic data of Titan with the UKIRT CGS4 spectrometer. We discovered two unexpected and unexplained spectral features in the 3-4 micron spectrum of Titan. An apparent emission feature near the 3 micron (nu3) band of methane indicates temperatures higher than known to be present in Titan's upper stratosphere and may be caused by unexpected non-LTE emission. An absorption feature near 3.47 microns may be caused by absorption in solid grains or aerosol's in Titan's clouds. The feature is similar, but not identical to organics in the interstellar matter and in comets. Anticipated Work Beyond the Termination of the Grant We are currently preparing the latest Titan results for publication. The new results will be followed up with further observations at the UKIRT and the IRTF telescopes. During the course of the present grant we also prepared a plan for new observation of CO and other rare constituents in Jupiter and Saturn. The work will initially consist of spatially resolved observations of the disk of Jupiter with the IRTF's CSHELL spectrometer. We expect to get spectra of at least 50 regions across Jupiter's disk. This unparalled spatial (and frequency) resolution should allow us to make significant progress in understanding the origins of trace compoundsandtheirchemistryin Jupiter. If theJovianobservalionsaresuccessful,weplan to follow with obse_'ationsof Saturn. At thetime thatthisobservingprogram wasdefined, we learnedof theimpending Shoemaker- Lcvv comctimpacton Jupiter. Wewill participatein thecampaigntoobserve this event,concentratingon spectroscopyof Jupiterbefore, duringandafterthe collisions. Theseplannedobsem'ationsarefundedundera separategrantthrough NASA's Solar SvstcmExplorationDivision, Office of SpaceScienceandapplications. Inventions There were no inventions completed under this grant. Publications Noll. K.S. and Knackc. R.F.. 1992, "Titans Mid-IR Albedo: New Observations from 3 to 5 microns." in Proceedings Syrnposium on Titan, ESA SP-338. --- 19_3. "Titan: 1-5 micron Photometry and Spectrophotometry and a Search for Variability." Icarus. 101, 272. -3-