Mercury: Mid-infrared Spectroscopic Measurements of the Surface 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 Kerri Donaldson Hanna

November 20, 2006Mercury Data Review2 Mid-InfraRed Spectrometer and Imager (MIRSI) On loan from Boston University and maintained by IRTF Acquires both spectra and high- resolution, 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, 2006Mercury Data Review3 Mercury and Lunar Observation Parameters ObjectMercuryMoon Date April April 2006 Transit Time (GMT)19:0010:00 Wavelength region (  m) Phase  (  ) Fraction Illuminated (%) Diameter (  ) Earth dist (AU) Helio dist (AU) Sub-Earth long (  ) Sub-Solar long (  )

November 20, 2006Mercury Data Review4 Mercury Observations Daytime observations April , 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, 2006Mercury Data Review5 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 ultra- mafic composition ( wt. % SiO 2 ) Modeling required and underway

November 20, 2006Mercury Data Review6 Lunar Observations: Ground Truth Nightime observations April , 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 Copernicus Grimaldi Apollo 16 Mersenius C

November 20, 2006Mercury Data Review7 Grimaldi Basin Spectra Spectra are different: EM and TM in slightly different locations Notice differences centered at ~10.3  m 7.7  m Filter Image

November 20, 2006Mercury Data Review8 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, 2006Mercury Data Review9 Grimaldi and Laboratory Spectra Comparison Grimaldi spectral features denoted by down arrows repeated in lunar spectra Fine-grained Lunar Sample Apollo 12 maria soil Fine-grained Lunar Sample Apollo 16 highlands soil Grimaldi spectra similar to Norite.H2 spectra from  m We can begin chemical identification of lunar regions with no sample returns

November 20, 2006Mercury Data Review10 Actual Surface Chemistry SiO CaO6.43 TiO Na 2 O1.85 Al 2 O K2OK2O0.74 Fe 2 O H2OH2O3.16 FeO10.78 P2O5P2O MnO0.22 MgO12.95 TOTAL SiO TiO Al 2 O Cr 2 O FeO15.4 MnO0.22 MgO9.7 CaO10.4 Na 2 O0.43 K2OK2O0.24 H2OH2O0.00 P2O5P2O5 TOTAL SiO TiO Al 2 O Cr 2 O FeO4.55 MnO0.06 MgO5.02 CaO16.21 Na 2 O0.42 K2OK2O0.09 P2O5P2O5 0.1 S0.06 TOTAL100.6 LS (Morris et al., 1983) LS (Morris et al., 1983) Norite.H2 (ASTER Spectral Library)

November 20, 2006Mercury Data Review11 Mercury and Laboratory Spectra Comparison Local EM enstatite Both Mercury spectra have similar Na-rich feldspar feature to Sprague & Roush model Mercury ~ º W - local EM characterisitic of enstatite orthpyroxene, TM indicative of wt. %SiO 2 Mercury ~ º W TM indicative of wt. %SiO 2 ?

November 20, 2006Mercury Data Review12 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, 2006Mercury Data Review13 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, 2006Mercury Data Review14 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 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.