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(Click for frequent words.) 71 Martian soil 65 Gusev crater 65 Lander robotic arm 65 NASA Opportunity rover 65 Opportunity rover 64 martian rocks 63 martian surface 63 Orbiter MRO 63 microscopic imager 63 lander robotic arm 63 Saturnian moon Titan 63 rover Opportunity 62 NASA rover Spirit 62 lander 62 Martian surface 62 Mossbauer spectrometer 62 Orbiter LRO 62 Sensing Satellite LCROSS 62 Saturn moon 61 Mars CRISM 61 lunar soil 61 Meridiani 61 NASA rovers Spirit 61 NASA Spirit rover 60 polar craters 60 rover Spirit 60 Microscopy Electrochemistry 60 ejecta plume 60 APXS 60 Opportunity Mars rover 60 lunar crust 60 Martian landscape 60 Martian crater 59 Analyzer TEGA 59 miniature ovens 59 Martian arctic 59 clumpy soil 59 twin rover Opportunity 58 neutral mass spectrometer 58 NASA Mars Reconnaissance 58 twin rover Spirit 58 cometary dust 58 Martian dust 58 Phoenix lander 58 NASA Cassini spacecraft 58 Mars rover Opportunity 58 ESA Huygens probe 58 Mars Meridiani Planum 58 rock outcrop 58 Mössbauer 58 Meridiani Planum 58 Mössbauer spectrometer 58 martian 57 OMEGA instrument 57 crossbedding 57 lunar surface 57 comet dust 57 basaltic rock 57 Comet 9P/Tempel 1 57 Galileo spacecraft 57 Isidis Planitia 57 Jupiter moons Europa 57 jarosite 57 Mars Reconnaissance Orbiter 57 Spirit rover 57 lunar regolith 57 six wheeled rover 57 permanently shadowed craters 57 NASA rover Opportunity 56 Mars Gusev Crater 56 Alpha Particle 56 shadowed craters 56 Cassini flyby 56 Mossbauer 56 Mini TES 56 shepherding spacecraft 56 perchlorate salts 56 phyllosilicate 56 interstellar particles 56 Moessbauer spectrometer 56 Mars Reconnaissance Orbiter MRO 56 comet particles 56 Evolved Gas 56 lunar crater 56 Martian equator 56 Meridiani plains 56 magnesium sodium potassium 56 Rover Opportunity 56 Itokawa 56 NASA rovers 56 finely layered 56 bedrock outcropping 56 NASA Stardust spacecraft 56 Diviner 56 arctic plains 56 penetrating radar 56 Microscopic Imager 56 Nasa Mars Reconnaissance 55 spherules 55 Gusev Crater 55 Shepherding Spacecraft 55 impactor spacecraft 55 Endurance crater 55 Robotic Arm Camera 55 petrographic 55 comet nucleus 55 icy moons 55 silicate rocks 55 spacecraft Cassini 55 layered bedrock 55 interstellar dust grains 55 orbiting spacecraft 55 lunar craters 55 regolith 55 hypergolic 55 Mars moon Phobos 55 LCROSS spacecraft 55 ESA Mars 55 moondust 55 IBEX spacecraft 55 Terra Meridiani 55 X ray spectrometer 55 martian landscape 55 Jovian moons 55 Lunar Reconnaissance Orbiter LRO 55 Saturn moon Enceladus 55 Red Planet 55 TEGA oven 55 Rosetta spacecraft 55 mineralogical composition 55 rover robotic arm 55 Stardust spacecraft 55 MARSIS radar 55 WISE telescope 54 Martian atmosphere 54 laser altimeter 54 hematite mineral 54 WISE spacecraft 54 Phoenix Mars Lander 54 Martian terrain 54 martian atmosphere 54 Nasa Mars Odyssey 54 NASA MESSENGER spacecraft 54 asteroid Itokawa 54 robotic rover Spirit 54 Nasa spacecraft 54 gamma ray spectrometer 54 lunar magma 54 Compact Reconnaissance Imaging Spectrometer 54 Phoenix Mars lander 54 Martian permafrost 54 onboard Chandrayaan 54 Mars Color Imager 54 NASA Voyager spacecraft 54 exosphere 54 rock abrasion 54 robotic explorer 54 HiRISE image 54 phyllosilicates 54 ferric oxides 54 Vastitas Borealis 54 lunar equator 54 airglow 54 spacecraft flyby 54 Sojourner rover 53 mineral hematite 53 Opportunity rovers 53 lander rover 53 robotic geologist 53 Mars Orbiter Camera 53 gray hematite 53 TEGA instrument 53 motorized rasp 53 olivine mineral 53 Mars Odyssey spacecraft 53 outer corona 53 Huygens probe landed 53 smoggy atmosphere 53 Phoenix Microscopy Electrochemistry 53 vast Gusev Crater 53 Sensing Satellite 53 Cabeus crater 53 Endurance Crater 53 planet magnetosphere 53 ejecta blanket 53 infrared spectrometer 53 subsurface ocean 53 Martian plains 53 NASA Lunar Reconnaissance 53 EPOXI spacecraft 53 moon Phobos 53 NASA Mars Odyssey 53 Nili Fossae 53 icy comets 53 Rover Spirit 53 turbidites 53 Candor Chasma 53 Dodo Goldilocks 53 alpha particle X ray 53 periodic dimming 53 flyby spacecraft 53 thermal emission spectrometer 53 scoopful 53 seafloor sediment 53 asteroid Eros 53 yardangs 53 martian meteorites 53 stationary lander 53 mineral olivine 53 Mars Pathfinder lander 53 NASA Mars rover 53 Cabeus 52 comet Wild 52 HiRISE images 52 icy crust 52 gaseous planet 52 rovers Spirit 52 Mars lander 52 orbiting Mars 52 Stardust comet 52 Syrtis Major 52 silicate dust 52 Viking landers 52 trench informally 52 NASA EPOXI mission 52 Comet Hartley 2 52 slender crescent 52 moon Europa 52 tholins 52 Ranging spacecraft 52 Martian rocks 52 volcanic basalt 52 heavily cratered 52 spectrographic 52 Venusian atmosphere 52 Mars Lander 52 rover 52 LCROSS 52 basaltic rocks 52 Pancam 52 solidified lava 52 iron sulfate 52 MARSIS 52 cometary 52 Martian polar 52 Mars Orbiter Laser Altimeter 52 permanently shadowed regions 52 Mini Thermal Emission 52 graphite whiskers 52 silicates 52 spectroscopic analysis 52 cometary material 52 PASADENA Calif. NASA 52 Express orbiter 52 Lunar CRater Observation 52 NASA twin rovers 52 Mercury flyby 52 meteorite fragments 52 Foton M3 52 Mars orbiting spacecraft 52 robotic lander 52 Lunar Prospector 52 Thermal Emission Spectrometer 52 unmanned Chandrayaan 52 geoneutrinos 52 LCROSS mission 52 spacecraft thrusters 52 Cassini flybys 52 NASA Cassini 52 cryovolcanism 52 comet nuclei 52 Terra Sirenum 52 ah dus 52 hydrated minerals 52 Stardust capsule 52 Huygens lander 52 rover Spirit landed 52 orbiting Mars Odyssey 52 called gray hematite 52 Martian orbit 51 THEMIS Images 51 geyser plumes 51 stony meteorites 51 concretions 51 moon permanently shadowed 51 Mars Opportunity rover 51 copper impactor 51 spectroscopically 51 Rock Abrasion Tool 51 iron sulphate 51 Hayabusa spacecraft 51 comet McNaught 51 moon Titan 51 ejecta curtain created 51 magma ocean 51 Mars rovers Spirit 51 sediments deposited 51 calcite crystals 51 Messenger spacecraft 51 permanently shadowed lunar 51 spacecraft orbited 51 basalt rocks 51 anorthosite 51 irregularly shaped asteroid 51 lunar meteorites 51 volcanic moon Io 51 Whillans Ice Stream 51 Imaging Spectrometer 51 Hubble observations 51 moon Enceladus 51 Explorer WISE 51 situ measurements 51 Bonneville Crater 51 hydroxyl molecules 51 Valles Marineris 51 Conductivity Analyzer 51 interstellar dust 51 polygon patterns 51 sedimentary deposits 51 Context Camera 51 Spirit Mars rover 51 Martian arctic plains 51 MESSENGER spacecraft 51 Victoria Crater 51 Itokawa asteroid 51 Lunar Crater Observation 51 Jupiter Ganymede 51 micrometre sized 51 spacecraft orbiting 51 Cassini spacecraft 51 Optical Microscope 51 planetesimals 51 THEMIS Image 51 NASA Lunar Crater 51 NASA Lunar Prospector 51 Ares Vallis 51 Mars Odyssey orbiter 51 Earth ionosphere 51 layered outcrops 51 lunar orbiters 51 abyssal plains 51 Saturnian moon 51 Mazatzal 51 Saturn moon Iapetus 51 igneous rocks 51 Lunar Excursion Module 51 retroreflector 51 O OREOS 51 retrograde orbit 51 refrozen ice 51 Martian rovers 51 Jupiter icy moons 51 NASA LCROSS 51 olivine rich 51 Planetary Fourier Spectrometer PFS 51 Jovian moon 51 seafloors 51 interstellar dust particles 51 Hellas Basin 51 crystalline silicates 51 Descent Imager Spectral Radiometer 51 COROT 7b 51 thin crescent 51 ejecta 51 geochemical assay 51 sulfate salts 50 carbonate minerals 50 Nasa Deep Impact 50 Enceladus flyby 50 isotopic ratios 50 Ares IX rocket 50 Cloud Aerosol Lidar 50 Titan flybys 50 Cassini orbiter 50 pebble sized 50 Impact Probe MIP 50 Moderate Resolution Imaging 50 ESA Rosetta 50 rubbly 50 GRACE satellites 50 lobate 50 Comet Hartley 50 overlying layers 50 Venusian surface 50 shadowy craters 50 planet Gliese #g 50 ExoMars rover 50 KBOs 50 gaseous planets 50 Mars Orbiter 50 Martian gullies 50 HiRISE camera 50 DISR 50 mantle lithosphere 50 meteoritic material 50 polarimetry 50 Aram Chaos 50 simulated lunar 50 Ulysses spacecraft 50 unmanned probes 50 Huygens probe 50 Infrared Pathfinder Satellite 50 Rosetta orbiter 50 sub glacial lakes 50 Comet Halley 50 spectrometers 50 journal Meteoritics 50 Yinghuo 1 50 Mars Odyssey Orbiter 50 Rover MER 50 interstellar grains 50 Martian lander 50 Curiosity rover 50 Martian dunes 50 Martian craters 50 spacecraft 50 jagged ridge 50 SHARAD 50 reentry capsule 50 lunar orbiting spacecraft 50 Taurus Littrow Valley 50 lunar highlands 50 crustal thickness 50 lunar dust 50 Shackleton crater 50 Mission SRTM 50 comet Hartley 2 50 Asteroid Itokawa 50 Io volcanoes 50 Saturn moons Enceladus 50 WISE infrared 50 Shuttle Radar Topography 50 comet Churyumov Gerasimenko 50 zinc sulfide 50 Clementine spacecraft 50 Imaging Spectroradiometer MODIS instrument 50 penumbral shadow 50 protruding thermal 50 polar layered 50 GJ #b [002] 49 VIRTIS 49 galactic disk 49 liquid ethane 49 asthenosphere 49 moonquakes 49 Saturn Cassini 49 Bug Nebula 49 THEMIS satellites 49 Epoxi 49 Huygens Probe 49 protoplanets 49 Ranging MESSENGER spacecraft 49 Comet Boethin 49 probe Huygens 49 Moderate Resolution 49 Galilean satellites 49 ESA ASI 49 lobate scarps 49 Solar Dynamics Observatory 49 silicate minerals 49 aboard Taurus XL 49 interferometric synthetic aperture radar 49 Lake Vostok 49 Planck spacecraft 49 permanently shadowed 49 interstellar dust samples 49 Robotic Arm 49 moon Io 49 Mercury magnetosphere 49 Comet #P/Churyumov-Gerasimenko 49 orbited Jupiter 49 Mars rovers Opportunity 49 Climate Experiment GRACE 49 Cryosat 49 Saturn rings 49 comets asteroids 49 lander Robotic Arm 49 Widely spaced 49 SPICAM 49 Cometary 49 infrared spectrometers 49 THEMIS spacecraft 49 GOCE satellite 49 asteroid Steins 49 Hayabusa probe 49 ultramafic intrusives 49 gamma rays emitted 49 Cassini spacecraft orbiting 49 elongated orbits 49 glacial sediments 49 lunar orbiter Chandrayaan 49 polar vortex 49 spheroidal 49 asteroidal 49 BIF outcrops 49 LCROSS Lunar Crater Observation 49 comet flyby 49 Saturnian system 49 NEAs 49 bedrock outcrops 49 spectrometric 49 New Horizons spacecraft 49 comets orbiting 49 sediment samples 49 plagioclase 49 Huygens descent 49 orbiter 49 Wilkinson Microwave Anisotropy Probe 49 Methane hydrate 49 rover panoramic 49 Mars landers 49 Martian meteorites 49 Odyssey orbiter 49 Arabia Terra 49 http:/saturn.jpl.nasa.gov 49 Mathieu Amalric stumbles 49 spatially resolved 49 fainter objects 49 cumulus cloud 49 Comet Tempel 1 49 rover Sojourner 49 Ray Spectrometer 49 neutron spectrometer 49 glacial till 49 STEREO spacecraft 49 Miniature Thermal Emission 49 exhaust plume 49 telescopic observations 49 shuttle underbelly 49 Planck satellite 49 ionized particles 49 cesium vapor 49 Spectrometers 49 Evolution Explorer 49 argillic altered 49 iron oxides 49 unmelted 49 cometary impacts 49 Mount Bosavi 49 McMurdo Dry Valleys 49 cometary nucleus 49 ammonia flakes 49 Saturn moons Titan 49 Earth asteroid Itokawa 49 melt inclusions 49 orbiting Saturn 49 LORRI 49 TEGA 49 Titan Saturn 49 visit http:/saturn.jpl.nasa.gov 49 CRISM 49 olivines 49 moons Europa 49 planemos 49 MESSENGER 49 Martian rover 48 sterile neutrino 48 Viking orbiters 48 craters 48 Reiner Gamma 48 infrared spectrograph 48 Martian 48 Ionosphere Sounding 48 Conductivity Analyzer MECA 48 Comet Tempel Tuttle 48 circumstellar 48 ray Space Telescope 48 Cassini 48 Planitia 48 heatshield 48 Dodo Goldilocks trench 48 circumstellar disk 48 proto planetary disk 48 lakebed sediments 48 sister rover Spirit 48 #P/Churyumov-Gerasimenko 48 Saturn Enceladus 48 flyby 48 asteroid Vesta 48 panoramic camera 48 waning crescent 48 planetary Transits 48 volcanic plumes 48 salt crystals 48 Deep Impact probe 48 spacecraft Chandrayaan 1 48 Saturnian moons 48 Cassini Huygens spacecraft 48 northern arctic plains 48 spectrographs 48 galaxies collide 48 CryoSat mission 48 cometary debris 48 MG J# +# 48 Composite Infrared Spectrometer 48 rubidium vapor 48 silicon monoxide 48 dubbed Dodo Goldilocks 48 Neutron Spectrometer 48 unweathered 48 HRSC 48 molten rocks 48 Jonathan Lunine 48 High Resolution Imaging 48 Philae lander 48 astrobiological 48 chondritic meteorites 48 clumpiness 48 Saturn moon Mimas 48 biosignatures 48 zodiacal light 48 gradiometer 48 AMSR E 48 gray hematite mineral 48 primordial ingredients 48 lander Beagle 2 48 Jovian atmosphere 48 magnetometry 48 NASA ICESat 48 HiRISE 48 basalt volcanic 48 X ray Spectrometer 48 Huygens mission 48 starquakes 48 orbiting observatories 48 Phoebe orbits 48 goethite 48 magmas 48 claystone 48 infrared telescopes 48 drogue parachute 48 Deep Impact flyby spacecraft 48 Martian moons Phobos 48 Mars rover 48 angular boulders 48 Mercury exosphere 48 quartz feldspar porphyry intrusive 48 rock outcrops 48 stromatolite 48 Elysium Planitia 48 Oort cloud 48 outcrop exposures 48 ESA SMART 48 comet Lulin 48 polarimetric 48 seabed sediments 48 Neutron Detector 48 Neutral Mass Spectrometer 48 Mars Squyres 48 metamorphic rock 48 Rosetta lander 48 Murchison meteorite 48 Phobos 48 lunar orbits 48 Antarctic Dry Valleys 48 Orbiter 48 smallest exoplanet 48 hydrated silica 48 carbonaceous material 48 limonitic 48 shielding tiles 48 occultations 48 Fomalhaut b 48 NFIRE 48 planets comets 48 Stadermann 48 XMM Newton satellite 48 X ray telescopes 48 Enceladus icy 48 COROT 48 Diviner instrument 48 microfossil 48 carbonaceous chondrite 48 silicate grains 48 subglacial 48 Voyager spacecraft 48 Mini SAR 48 Saturn moons 48 Mars Global Surveyor 48 carbon isotope ratios 48 Io Europa 48 Moon Mineralogy Mapper 48 Resolution Stereo Camera 48 Jupiter moons 48 dust devils 48 crystallites 48 Enceladus 48 Viking Lander 48 Deep Impact craft 48 sulfur isotope 48 subhorizontal 48 aerosol particles 48 smoothest flattest spot 48 magnetospheric 48 Ontario Lacus 48 abyssal plain 48 Erebus Crater 48 subducted 48 carbonate globules 48 Doppler measurements 48 scarps 48 EPOCh 48 Infrared Thermal Imaging Spectrometer 48 spectral signatures 48 orbiting observatory 48 THEMIS 48 claylike 47 magnetotail 47 Upsilon Andromedae 47 Phobos Grunt 47 KAGUYA 47 mineralogical studies 47 Galaxy Evolution 47 albedo reflectivity 47 Infrared Array Camera 47 comet tail 47 NASA Mars Orbiter 47 Kuiper belt objects 47 graphene sheet 47 flyby Cassini 47 meteoritic 47 meteor impacts 47 ESA Envisat satellite 47 windblown sand 47 robotic geologists 47 Global Surveyor spacecraft 47 permanently shadowed crater 47 airborne particles affect 47 orbiter Cassini 47 Corot 7b 47 Moessbauer 47 Cassini Huygens 47 planets asteroids 47 Orbiting Carbon Observatory 47 Endeavour thermal shielding 47 accretion disks 47 Shackleton Crater 47 Mars orbiter 47 Trojan asteroids 47 gamma ray observatory 47 thruster firings 47 Herschel Space Telescope 47 ICESat 47 legged lander 47 subsurface 47 Graphene oxide 47 specular reflection 47 Multi Object Spectrometer 47 Earthlike 47 simulated Martian 47 CloudSat 47 hematite goethite 47 smoothest flattest 47 earthshine 47 saprolitic 47 moon Charon 47 ferrous oxide 47 Guatemala Pacaya volcano 47 mineralized peridotite 47 Iapetus 47 http:/www.nasa.gov/cassini 47 resistant tiles 47 Near Infrared Camera 47 Huygens 47 Observatory SDO 47 Moon Mineralogy Mapper M3 47 DEPTHX 47 noctilucent clouds 47 planetary surfaces 47 NASA Wilkinson Microwave 47 Mars 47 SMOS 47 spectroscopic measurements 47 evaporite 47 mineralogical 47 geysers erupting 47 crater 47 Miniature Synthetic Aperture Radar 47 lunar explorer 47 whiz harmlessly 47 auger drill 47 subglacial lakes 47 scanning optical microscopy 47 pillow lava 47 hydrothermal fluid 47 microbialites 47 Transantarctic Mountains 47 magnetic monopoles 47 TRMM Microwave Imager TMI 47 Deep Impact eXtended Investigation 47 atomically flat 47 GJ#b 47 closest flyby 47 Solar TErrestrial RElations Observatory 47 interferograms 47 Jet Propulsion Laboratory JPL 47 NASA ESA Hubble 47 silicate mantle 47 LRO spacecraft 47 microscopic bubbles 47 extrasolar 47 orbiting gamma ray 47 sulphates 47 Reflection Radiometer 47 Global Surveyor 47 equatorial latitudes 47 piggybacked Huygens probe 47 micrometre 47 robotic landers 47 orbiting Hubble Space Telescope 47 orbiter robotic arm 47 radar interferometry 47 Titan flyby 47 polar plateau 47 volcanic tuff 47 Chryse Planitia 47 cenospheres 47 scintillometer surveys 47 ultraviolet wavelengths 47 Geochemical analysis 47 RQ# 47 Tempel 1 47 outcrop 47 dirty snowballs 47 Cassini ion 47 Planck telescope 47 GSLV D3 rocket 47 stream sediment geochemical 47 micro meteorites 47 manganese oxide 47 LADEE 47 SINFONI 47 Surface Stereo Imager 47 Neptune Uranus 47 pyroclastics 47 ultraviolet imaging spectrograph 47 dolerite 47 NASA Cassini orbiter 47 pyritized 47 Regolith 47 micrometer sized 47 Advanced Microwave Scanning 47 halite 47 steel shavings clogging 47 geophysics prospecting 47 Envisat satellite 47 tonalite 47 nanoribbon 47 basaltic 47 Anisotropy Probe 47 meter diametre 47 recrystallized 47 Aqua satellite 47 ALH# 47 lightweight synthetic aperture 47 Aqua satellites 47 crustal rocks 47 Palaeozoic sedimentary 47 volcano Olympus Mons 47 cratered highlands 47 Kuiper Belt Objects 47 binary asteroid 47 GALEX 46 LISA Pathfinder 46 Purgatory Dune 46 robotic rovers 46 swirling dust devils 46 Samuel Oschin Telescope 46 carbonaceous chondrites 46 Endeavour Crater 46 calcrete 46 Ocean Salinity SMOS 46 EPOXI mission 46 silty 46 Bullet Cluster 46 robotic arm 46 spectral bands 46 Panoramic Camera 46 Comet Churyumov Gerasimenko 46 Earth orbiting satellites 46 Keck Interferometer 46 asteroids comets 46 thermal convection 46 comet 46 distant supernovae 46 Earthlike planets 46 Characterization EPOCh 46 soil geochemical surveys 46 Kepler spacecraft 46 mantle plumes 46 pediment gravels 46 exoplanetary systems 46 lensing galaxy 46 Imaging Spectroradiometer MODIS 46 rotational axis 46 Hematite Slope 46 mineralized boulders 46 IP Resistivity survey 46 moonlets 46 Stardust mothership 46 gravitational tugs 46 olivine crystals 46 oxygen isotopes 46 Infrared Mapping Spectrometer 46 anomalies coincident 46 Walruses dive 46 UAVSAR 46 electromagnetic signals 46 Institute MBARI 46 Weddell Sea 46 Planetary Transits 46 Lunar Crater 46 filamentary structure 46 Cosmic Microwave Background 46 elemental abundances 46 cobalt atoms 46 Titan smoggy 46 Science Experiment HiRISE 46 conglomeratic 46 SIRTF 46 silicified limestone 46 protoplanet 46 NASA Kepler telescope 46 bathymetry 46 WMAP satellite 46 Commander Dmitry Kondratyev 46 magma chambers 46 acid leached 46 Infrared Mapping Spectrometer VIMS 46 vugs 46 STSS Demo 46 vapor plume 46 Advanced Synthetic Aperture 46 Mars Pathfinder 46 Convection Rotation 46 antineutrinos 46 icy moon Enceladus 46 ancient lakebed awash 46 shuttle underside 46 granitic basement 46 basalts 46 Martian volcanoes 46 Flyby spacecraft 46 pyroxene 46 look distractingly cartoony 46 magnetopause 46 outcrop samples 46 fluid inclusions 46 meteoroids 46 vaporises 46 hummocks 46 olivine 46 orbit insertion 46 rovers 46 wavefronts 46 Galilean moons 46 comet Tempel Tuttle 46 filamentary structures 46 outer planets 46 maritime subsurface 46 Hubble Space Telescopes 46 kimberlitic material 46 laser altimetry 46 advection 46 Upsilon Andromedae b 46 explosive volcanism 46 conductive zones 46 coverslip 46 Discovery thermal shielding 46 moons Phobos 46 cobalt atom 46 remote sensing instruments 46 Mars Odyssey 46 molten magma 46 Titanic hull 46 NFIRE satellite 46 Viking Orbiter 46 Wilkinson Microwave Probe 46 entered lunar orbit 46 protoplanetary disk 46 planets orbits 46 cryosphere 46 NEAR Shoemaker 46 reconnaissance orbiter 46 # Apophis 46 microscopic crystals 46 Fermi telescope 46 Neutron stars 46 chondritic 46 NASA Spacecraft 46 infrared observatory 46 LRO 46 radio occultation 46 Multi Object Spectrograph 46 robot rovers 46 planetary nebulas 46 twin rovers Spirit 46 volcaniclastic kimberlite 46 waning gibbous