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Mercury: Mid-infrared Spectroscopic Measurements of the Surface Kerri Donaldson Hanna A. L. Sprague 1, Mercury: Mid-infrared Spectroscopic Measurements of the Surface Kerri Donaldson Hanna A. L. Sprague 1, R. W. Kozlowski 2, K. Boccafolo 2, J. Helbert 3, A. Maturilli 3, and J. Warell 4 1 University of Arizona, Tucson, AZ, 2 Susquehanna University, Selingsgrove, PA, 3 Institute of Planetary Research - DLR, Germany, and 4 Uppsala University, Sweden November 20, 2006 Mercury Data Review

Mid-Infra. Red Spectrometer and Imager (MIRSI) • On loan from Boston University and maintained Mid-Infra. Red Spectrometer and Imager (MIRSI) • On loan from Boston University and maintained by IRTF • Acquires both spectra and highresolution, multi-wavelength images • 2 grisms: 10 m (8 -14 m) and 20 m (17 -26 m) • 10 m - resolution of 200 • Slit size of 0. 6 • Large field of view (85 x 64 ) and diffraction-limited seeing of 0. 8 • Imaging mode spectral resolution up to 1% bandwidth • Narrow and broad band filters for 10 and 20 m windows and a CVF November 20, 2006 Mercury Data Review 2

Mercury and Lunar Observation Parameters Object Mercury Moon Date 7 - 11 April 2006 Mercury and Lunar Observation Parameters Object Mercury Moon Date 7 - 11 April 2006 14 - 16 April 2006 Transit Time (GMT) 19: 00 10: 00 Wavelength region ( m) 8 - 14 Phase ( ) 9. 5 - 32. 6 93. 7 - 86. 7 Fraction Illuminated (%) 46 - 53 100 - 90 Diameter ( ) 7. 9 - 7. 4 30. 4 Earth dist (AU) 0. 85 - 0. 92 0. 00265 Helio dist (AU) 0. 466 1. 005 Sub-Earth long ( ) 172 - 196 356 - 353 Sub-Solar long ( ) 266 - 282 360 - 320 November 20, 2006 Mercury Data Review 3

Mercury Observations • Daytime observations April 7 - 11, 2006 • Mercury observed longitudes Mercury Observations • Daytime observations April 7 - 11, 2006 • Mercury observed longitudes included Caloris Basin and Mariner 10 un-imaged longitudes • MIRSI slit easily positioned over Mercury’s illuminated disk using filter image mode November 20, 2006 Mercury Data Review 4

Mercury Spectra • Spectra from all five regions are very different • Local EM Mercury Spectra • Spectra from all five regions are very different • Local EM and TM wavelengths vary for each spectra • West of Caloris Basin - TM at 12. 6 m indicative of ultramafic composition (3440 wt. % Si. O 2) • Modeling required and underway November 20, 2006 Mercury Data Review 5

Lunar Observations: Ground Truth • Nightime observations April 14 - 16, 2006 • Locations Lunar Observations: Ground Truth • Nightime observations April 14 - 16, 2006 • Locations on the lunar surface with well known composition from near-infrared telescopic observations and Apollo sample returns chosen • Same observing configuration as Mercury November 20, 2006 Copernicus Grimaldi Mercury Data Review Apollo 16 Mersenius C 6

Grimaldi Basin Spectra 7. 7 m Filter Image • Spectra are different: EM and Grimaldi Basin Spectra 7. 7 m Filter Image • Spectra are different: EM and TM in slightly different locations • Notice differences centered at ~10. 3 m November 20, 2006 Mercury Data Review 7

Comparison Laboratory Spectra • Spectra of Apollo return samples of varying grain sizes from Comparison Laboratory Spectra • Spectra of Apollo return samples of varying grain sizes from RELAB spectral library from Brown University studied • Spectra of rocks and minerals for known lunar surface units from ASTER spectral library studied • True emission spectra of fine grain size minerals from Berlin Emissivity Database studied • Laboratory reflectance spectra were converted to emittance spectra using approximation to Kirchoff’s relation E = 1 - R November 20, 2006 Mercury Data Review 8

Grimaldi and Laboratory Spectra Comparison • Grimaldi spectral features denoted by down arrows repeated Grimaldi and Laboratory Spectra Comparison • Grimaldi spectral features denoted by down arrows repeated in lunar spectra • Fine-grained Lunar Sample 12030. 135 - Apollo 12 maria soil • Fine-grained Lunar Sample 61221. 79 - Apollo 16 highlands soil • Grimaldi spectra similar to Norite. H 2 spectra from 11 - 13 m • We can begin chemical identification of lunar regions with no sample returns November 20, 2006 Mercury Data Review 9

Actual Surface Chemistry Norite. H 2 (ASTER Spectral Library) LS 12030. 135 (Morris et Actual Surface Chemistry Norite. H 2 (ASTER Spectral Library) LS 12030. 135 (Morris et al. , 1983) LS 61221. 79 (Morris et al. , 1983) Si. O 2 48. 23 Si. O 2 46. 6 Si. O 2 45. 35 Ca. O 6. 43 Ti. O 2 3. 6 Ti. O 2 0. 49 Ti. O 2 1. 1 Al 2 O 3 14. 2 Al 2 O 3 28. 25 Na 2 O 1. 85 Cr 2 O 3 0. 35 Cr 2 O 3 0. 00 Al 2 O 3 12. 31 Fe. O 15. 4 Fe. O 4. 55 K 2 O 0. 74 Mn. O 0. 22 Mn. O 0. 06 Fe 2 O 3 2. 36 Mg. O 9. 7 Mg. O 5. 02 H 2 O 3. 16 Ca. O 10. 4 Ca. O 16. 21 Fe. O 10. 78 Na 2 O 0. 43 Na 2 O 0. 42 P 2 O 5 0. 06 K 2 O 0. 24 K 2 O 0. 09 Mn. O 0. 22 H 2 O 0. 00 P 2 O 5 0. 1 Mg. O 12. 95 P 2 O 5 0. 00 S 0. 06 TOTAL 100. 19 TOTAL 101. 14 TOTAL 100. 6 November 20, 2006 Mercury Data Review 10

Mercury and Laboratory Spectra Comparison • Local EM enstatite • Both Mercury spectra have Mercury and Laboratory Spectra Comparison • Local EM enstatite • Both Mercury spectra have similar Na-rich feldspar feature to Sprague & Roush model • Mercury ~200 - 210º W local EM characterisitic of enstatite orthpyroxene, TM indicative of 40 - 46 wt. %Si. O 2 • Mercury ~225 - 235º W TM indicative of 34 - 40 wt. %Si. O 2 • ? November 20, 2006 Mercury Data Review 11

Work in Progress • Begin modeling Mercury and Lunar surfaces with fine grain emission Work in Progress • Begin modeling Mercury and Lunar surfaces with fine grain emission spectra provided by the Planetary Emissivity Laboratory, DLR, Berlin. • Courtesy of Joern Helbert and Alessandro Maturilli November 20, 2006 Mercury Data Review 12

Conclusions • Mercury spectra corroborate a heterogeneous surface composition • Grimaldi Mare and Highlands Conclusions • Mercury spectra corroborate a heterogeneous surface composition • Grimaldi Mare and Highlands spectra permit diagnostic surface chemistry • Modeling Mercury spectra will permit diagnostic surface chemistry November 20, 2006 Mercury Data Review 13

Acknowledgements Donaldson Hanna, Sprague, Kozlowski, Boccafolo and Warell were Visiting Astronomers at the NASA Acknowledgements Donaldson Hanna, Sprague, Kozlowski, Boccafolo and Warell were Visiting Astronomers at the NASA Infrared Telescope Facility which is operated by the University of Hawaii under contract from the National Aeronautics and Space Administration This work was supported by NSF grant AST-0406796 to Sprague Reproduced from the ASTER Spectral Library through the courtesy of the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California. © 1999, California Institute of Technology. ALL RIGHTS RESEREVED. November 20, 2006 Mercury Data Review 14