PowerPoint PresentationQuestions answered by studying surface compositionCommon minerals on planetary surfacesMercury versus the MoonMariner 10 ObservationsRe-calibration of Mariner 10 ImagesSlide 7Remote Sensing of Planetary BodiesRemote Sensing of Planetary BodiesVisible to Near-IR spectroscopyVisible to Near-IR resultsMid-IR spectroscopyDiagnostic Spectral FeaturesGrain Size and Composition Effects in the Mid-IRMid-IR resultsObserving Mercury and the Moon in the mid-IRHow does a spectrometer work?The Moon - Grimaldi BasinGrimaldi and Laboratory Spectra ComparisonMercurySlide 21Spectral deconvolution results for MercuryWhat do and don’t we really know?MESSENGERMercury’s Surface CompositionKerri Donaldson HannaQuestions answered by studying surface compositionWhat type of geologic history has Mercury undergone?•This would constrain the thermal evolution of the planetHow much FeO is on the surface?•This would constrain the evolution models discussed last weekHow much space weathering has occurred on Mercury’s surface?•This would constrain the space environment of the planet over its historyDoes any of the material in the exosphere come from Mercury’s surface?•This would constrain the interactions between the exosphere and the magnetic field, solar wind, and/or surfaceCommon minerals on planetary surfaces•Feldspars [(K,Ba,Ca,Na)Si3O8]•Two groups: K - Ba solutions and Ca - Na solutions (plagioclase)•Anorthite most abundant plagioclase on the Moon•Pyroxenes [(Mg,Fe,Ca)(Mg,Fe)Si2O6]•Two groups: orthopyroxenes and clinopyroxenes•Fe-rich, Mg-rich, Ca-rich, NaAl-rich, and CaMn-rich•Olivines [(Mg,Fe)2SiO4]•Common in the mantle on Earth•Solid solution between Mg-rich and Fe-rich•Fe-Ti Oxides [FeO, TiO2, FeTiO3]•Other minerals include sulfates, sulfides, carbonates, amphiboles, micas•On Mercury no plate tectonics or hydrologic cycle, should expect rocks and minerals that are associated with the crystallization of magma, possible igneous intrusions, and meteorite impact melting, fracturing, and mixingMercury versus the Moon•Originally Mercury thought to be similar to the Moon•Bright craters and dark plains•Smooth plains associated with impact craters and basinsMariner 10 Observations•No observations made that could determine elemental abundances, specific minerals, or rock types on Mercury•Mariner 10 observed day side albedos of Mercury and the Moon •Dark plains would have a lower albedo than a bright crater•Mercury’s albedo lower overall than the Moon’s by a few percent, but in the visible it has a higher albedo•Mercury’s albedo varies across its surface and at different wavelengths from 400 to 700 nm•Composition, grain size, and porosity plays key roles in explaining a planet’s albedo•Finely crystalline silicates low in Fe and Ti tend to be brighter and scatter more light off of the surface•New measurements from SOHO paired with Mariner 10 data looked at phase angle and backscattering•Results indicate Mercury’s surface has smaller grains and more transparent than the Moon, and the higher efficiency of reflecting light towards the sun indicates the presence of complex or fractured grainsRe-calibration of Mariner 10 Images•Technique first used on lunar data•Robinson and Lucey 1997•Use 375nm (UV) and 575nm (VIS) bands•Ratio UV/VIS•Plot UV/VIS versus VIS•As FeO increases and soils mature spectrum reddens and UV/VIS decreases•As opaque minerals increase the albedo decreases and increases the UV/VIS•Rotate axis to decouple FeO+maturity from opaque indexRe-calibration of Mariner 10 ImagesVIS imageUV/VIS image•Brighter tone indicate increasing bluenessFeO + maturity •Brighter tone indicate decreasing FeO and maturityOpaque Index •Brighter tone indicate increasing opaque mineralsRemote Sensing of Planetary BodiesRemote Sensing of Planetary Bodies Spectroscopy•Visible light (0.4 - 0.7 m)•Near-IR (0.7 - 2.5 m)•Mid-IR (2.5 - 13.5 m)Visible to Near-IR spectroscopy•Measuring reflected light•Absorption bands are created from electronic transitions in the molecules bonded in the lattices of silicates•Interested in 0.3 - 0.5 and 1.0m bands associated with FeO•Spectral contrast of features can be diminished due to space weathering•Spectral slope - indication of the maturity and composition•Fit straight line from 0.7 - 1.5m•Slope of line increases as soil matures •Look at ratios to determine soil maturity and FeO and opaque mineral content •Again -- techniques used originally on the MoonVisible to Near-IR results•Weak 1m band detected during 1 observation run - only in bright materials•Shape and width of 1m band indicative of Ca-rich clinopyroxene•Mercury’s spectral slope has a higher value than the spectral slope from immature to submature regions on the Moon•Low FeO (0 - 3%) and TiO2 (0 - 2%)Mid-IR spectroscopy•Measuring emitted light•Absorption bands are caused by the vibration, bending, and flexing modes of the crystalline lattices•Grain size and composition of mineral samples greatly affect spectra•Compare key spectral features diagnostic of composition with spectra of rocks and minerals measured in the laboratory•Reststrahlen bands - fundamental molecular vibration bands in the region from 7.5 - 11 mm•Emissivity maxima (also known as the Christensen feature) - associated with a silicate spectrum and occurs between 7 - 9 mm•Transparency minima - associated with the change from surface scattering to volume scattering and occurs between 11 - 13 mmGood indicator of SiO2 weight percent in rock•Highly depends on the quality of spectral libraries built from laboratory measurements of rocks and mineralsDiagnostic Spectral FeaturesCFRBTMGrain Size and Composition Effects in the Mid-IR Varying the composition changes the location of spectral features Varying the grain size changes the depth/or existence of spectral featuresMid-IR results•Mercury’s surface composition is heterogeneous•Most spectra match models of plagioclase feldspar with some pyroxene•Plagioclase more sodium-rich than that on the Moon•Pyroxene low-Fe, Ca-rich diopside or augite or low-Fe, Mg-rich enstatite•Bulk compositions indicate an intermediate silica content (similar to diorite or andesite on Earth)•No evidence for Fe- and/or Ti-bearing basalts as lava flows as seen on the MoonObserving Mercury and the Moon in the mid-IR• NASA Infared