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(Click for frequent words.) 71 NASA Stardust spacecraft 70 Comet Hartley 67 Stardust spacecraft 65 comet dust 64 asteroid Itokawa 64 Churyumov Gerasimenko 64 Comet #P/Churyumov-Gerasimenko 63 interstellar dust 63 cometary 62 comet nucleus 62 comet Churyumov Gerasimenko 62 cometary dust 62 comet Hartley 2 61 RQ# 61 Comet Hartley 2 61 EPOXI mission 61 #P/Churyumov-Gerasimenko 60 comet 60 interstellar dust grains 60 Itokawa asteroid 60 comet #P/Churyumov-Gerasimenko 60 Itokawa 60 comet particles 60 Comet Halley 60 NASA EPOXI mission 60 Galileo spacecraft 59 NASA Cassini spacecraft 59 NASA Voyager spacecraft 59 Cassini Huygens spacecraft 59 Ranging spacecraft 59 Orbiter LRO 59 asteroid Eros 59 Tempel 1 59 New Horizons spacecraft 58 Mars Reconnaissance Orbiter MRO 58 asteroid Steins 58 robotic Stardust spacecraft 58 Nasa spacecraft 58 icy comets 58 Messenger spacecraft 58 interstellar particles 58 CoRoT 58 asteroid Vesta 58 comet Tempel 1 58 Saturn Cassini 57 NASA Opportunity rover 57 Viking Lander 57 NASA MESSENGER spacecraft 57 Pluto Charon 57 NASA Wilkinson Microwave 57 MESSENGER spacecraft 57 Comet Tempel Tuttle 57 Enceladus 57 ESA Mars 57 ESA SMART 57 Lunar Reconnaissance Orbiter LRO 57 ESA Rosetta 57 NASA Lunar Prospector 57 Lunokhod 57 Deep Impact eXtended Investigation 57 rover Opportunity 57 orbited Jupiter 57 Comet Tempel 1 57 Titan flyby 57 innermost planet 57 Cassini Huygens 56 Earth asteroid Itokawa 56 hydroxyl molecules 56 spiral galaxy NGC 56 Martian rocks 56 Deep Impact craft 56 solar nebula 56 Voyager spacecraft 56 TrES 56 NASA Deep Impact 56 NASA LCROSS 56 comets 56 Kepler spacecraft 56 COROT 56 interstellar dust particles 56 moon Mab 56 ESA Huygens probe 56 interstellar dust samples 56 Martian arctic 56 Cassini flyby 56 Rosetta spacecraft 55 Orbiter MRO 55 Cassini spacecraft 55 ESA ERS 55 NASA twin rovers 55 Sensing Satellite LCROSS 55 outer planets 55 Cassini 55 CoRoT satellite 55 comet flyby 55 NASA Kepler telescope 55 comet chaser 55 comet tail 55 WISE mapped 55 Convection Rotation 55 Viking landers 55 Saturn moon 55 flyby spacecraft 55 Epoxi 55 spacecraft Cassini 55 antineutrinos 55 NASA MErcury Surface 55 Oort cloud 55 comet Shoemaker Levy 55 Epsilon Eridani 55 Kepler Space Telescope 54 ray Space Telescope 54 silicate dust 54 rover Spirit landed 54 Mars Odyssey orbiter 54 Murchison meteorite 54 Comet 9P/Tempel 1 54 Mössbauer 54 spacecraft flyby 54 Opportunity rover 54 Martian surface 54 NEAs 54 NASA Lunar Crater 54 Cabeus crater 54 NASA Kepler 54 neutral mass spectrometer 54 ESA Integral 54 Shoemaker Levy 54 constellation Carina 54 THEMIS Images 54 Hubble Space Telescope HST 54 comet McNaught 54 VIRTIS 54 protoplanetary disk 54 GJ #b [001] 54 planet TrES 54 planetesimals 54 ESA ASI 54 NASA ESA Hubble 54 WMAP satellite 54 Explorer WISE 54 CAIs 54 Virgo Cluster 54 Hayabusa capsule 54 Cosmic Microwave Background 54 Martian soil 54 sunlike star 54 Multi Object Spectrometer 54 comet Tempel Tuttle 54 permanently shadowed craters 54 smallest exoplanet 54 Swift Tuttle 54 MESSENGER 54 phyllosilicates 54 Apollo missions 54 Phoebe orbits 54 Sojourner Rover 54 Infrared Pathfinder Satellite 54 Corot 7b 54 planet Uranus 54 EPOXI spacecraft 54 impactor spacecraft 54 irregularly shaped asteroid 54 cometary material 53 nebular 53 Comet Lulin 53 Halley comet 53 Saturn moon Enceladus 53 ejecta 53 Jupiter magnetosphere 53 spatially resolved 53 lunar equator 53 Mars Pathfinder 53 exosphere 53 APXS 53 rover Spirit 53 closest flyby 53 Mars Odyssey spacecraft 53 Fomalhaut b 53 Huygens 53 Lutetia 53 solar corona 53 Nasa Deep Impact 53 Comet Hale Bopp 53 DISR 53 flyby 53 MG J# +# 53 comets asteroids 53 P Churyumov Gerasimenko 53 Cassini flybys 53 NASA rovers 53 Nasa Mars Reconnaissance 53 Servicing Mission 53 Deep Impact probe 53 Reconnaissance Orbiter 53 icy moons 53 Ulysses spacecraft 53 distant galaxies 53 Ocean Salinity SMOS 53 NASA Cassini 53 orbiting observatories 53 gamma ray spectrometer 53 WISE spacecraft 53 journal Meteoritics 53 retroreflector 53 constellation Aquarius 53 NASA Lunar Reconnaissance 53 Deep Impact spacecraft 53 orbiting Saturn 53 COROT 7b 53 LCROSS spacecraft 53 Global Surveyor 53 NASA Kepler spacecraft 53 Oort Cloud 53 Earth magnetotail 53 GA6 53 Martian atmosphere 52 galaxy NGC 52 martian soil 52 2 pronounced Vilt 52 weather satellite TIROS 52 Interior Laboratory GRAIL 52 Planetary Transits 52 O OREOS 52 exoplanetary 52 Martian equator 52 Aqua satellite 52 Wilkinson Microwave Probe 52 Investigation DIXI 52 exoplanets planets 52 Mars Pathfinder lander 52 lunar crust 52 Gusev crater 52 Isidis Planitia 52 olivines 52 XMM Newton 52 EPOCh 52 orbiting Hubble telescope 52 basaltic rocks 52 reentry capsule 52 Saturn moons 52 star Gliese 52 OSIRIS REx 52 asteroid 52 Planck spacecraft 52 Saturn rings 52 exo planet 52 orbiting spacecraft 52 gaseous planet 52 lunar soil 52 Heliospheric Observatory SOHO 52 LCROSS 52 Huygens mission 52 lander robotic arm 52 Stardust capsule 52 Stadermann 52 Mercury flyby 52 Kepler 9c 52 GRB #B 52 lunar craters 52 asteroid belt 52 Hayabusa spacecraft 52 Kuiper Belt 52 Field Planetary Camera 52 Phoenix lander 52 WASP #b 52 Jenniskens 52 extrasolar planets orbiting 52 Titan flybys 52 martian surface 52 Martian orbit 52 Stardust NExT 52 galaxy M# [001] 52 Anisotropy Probe 52 HD#b 52 NASA rovers Spirit 52 IBEX spacecraft 52 Hubble observations 52 NASA Spirit rover 52 ESA XMM Newton 52 micrometre sized 52 z ~ 52 interstellar cloud 52 planemos 52 Samuel Oschin Telescope 52 Martian arctic plains 52 Kepler Mission 52 STEREO spacecraft 52 Envisat satellites 52 Deep Impact comet 52 Rosetta orbiter 51 Bug Nebula 51 orbiting Mars 51 Martian craters 51 Saturnian moon Titan 51 Sojourner rover 51 PSR J# 51 Japan Hayabusa spacecraft 51 Antarctic Dry Valleys 51 Fermi telescope 51 ferric oxides 51 HD #b [002] 51 G#.# +#.# 51 NASA Mars Reconnaissance 51 twin Voyager spacecraft 51 CoRoT 7b 51 magma ocean 51 helium atoms 51 distant galaxy 51 EPOXI 51 Mars rovers Spirit 51 Enceladus flyby 51 P/# A2 51 cosmic microwave background 51 tiniest particles 51 interstellar grains 51 Adam Riess 51 lunar meteorite 51 galactic disk 51 onboard Chandrayaan 51 slender crescent 51 exoplanets orbiting 51 subsurface ocean 51 circumstellar disk 51 Earthly contamination 51 ESO PR 51 SuitSat 51 CRISM 51 lunar surface 51 stellar occultation 51 Meridiani plains 51 Mars Reconnaissance Orbiter 51 Hayabusa probe 51 HARPS spectrograph attached 51 Taurus Littrow Valley 51 quark gluon plasma 51 distant supernovae 51 Solar TErrestrial RElations Observatory 51 galaxy M# [002] 51 Space ENvironment GEochemistry 51 moon Enceladus 51 lunar meteorites 51 Opportunity Mars rover 51 Phobos 51 Lander robotic arm 51 substorm 51 martian atmosphere 51 Giovanni Cassini 51 telescopic observations 51 Venusian atmosphere 51 robotic explorer 51 Deep Impact Extended 51 Comet Churyumov Gerasimenko 51 Earth magnetosphere 51 known bird Archaeopteryx 51 gamma ray observatory 51 WD5 51 Wilkinson Microwave Anisotropy Probe 51 Venusian surface 51 rocky planets 51 NASA ICESat 51 sterile neutrino 51 millisecond pulsar 51 Martian crater 51 Chandrayaan 51 elliptical orbits 51 moonlet 51 Toutatis 51 asteroids 51 lunar regolith 51 ringed planet 51 supernova explosion 51 GEochemistry 51 Beta Pictoris b 51 stellar occultations 51 sulfur isotope 51 Cygnus X 51 Ranging MESSENGER spacecraft 51 northern arctic plains 51 Comet Boethin 51 interstellar molecules 51 Saturn outermost moon 51 NASA THEMIS 51 Cretaceous periods 51 LightSail 51 Saturnian moon 51 RXTE 51 Compact Reconnaissance Imaging Spectrometer 51 Compton Gamma Ray 51 jovian 51 Kuiper belt 50 Moderate Resolution Imaging 50 ESA Huygens 50 NASA Fermi Gamma 50 extrasolar planet 50 spectroscopic 50 planets orbiting sun 50 Meridiani 50 THEMIS satellites 50 sodium atoms 50 Nasa Kepler 50 Herschel Space Telescope 50 NASA STEREO 50 Lunar Prospector 50 HAT P 50 moon Titan 50 Comet #P 50 Planck satellite 50 Saturnian system 50 Near Infrared Camera 50 Titan Saturn 50 WISE infrared 50 Antennae Galaxies 50 distant quasar 50 Hesperian Epoch 50 protoplanets 50 Deep Impact flyby spacecraft 50 Asteroid Itokawa 50 Butterfly Nebula 50 Martian meteorites 50 heliosheath 50 Mercury magnetosphere 50 YU# 50 Rosetta lander 50 Foton M3 50 Mars CRISM 50 cosmic particles 50 laser altimeter 50 subatomic particles 50 Krimigis 50 perihelion 50 Meridiani Planum 50 permanently shadowed 50 impactor 50 martian 50 UA Lunar 50 circumstellar 50 Solar Dynamics Observatory 50 radial velocity 50 Elenin 50 Resolution Stereo Camera 50 organic molecules 50 planetary nebulae 50 DIXI 50 Jupiter flyby 50 copper impactor 50 Mars Orbiter 50 probe Chang'e 50 Radar ASAR 50 OGLE TR #b 50 outer corona 50 carbonaceous chondrite 50 Stardust comet 50 SN #A 50 CoRoT #b 50 lobate scarps 50 magnetic monopoles 50 Martian rovers 50 tau neutrinos 50 ALH# 50 moon Phobos 50 axions 50 muon neutrino 50 exoplanet 50 electron neutrinos 50 tiny meteoroid 50 exo planets 50 polarimetry 50 Comet Holmes 50 HiRISE camera 50 rovers Spirit 50 planets comets 50 trillionths 50 asteroids orbiting 50 photosphere 50 twin Viking landers 50 Pancam 50 interplanetary dust 50 noctilucent clouds 50 X ray spectrometer 50 Kiruna Sweden 50 Extrasolar Planet Observation 50 moon permanently shadowed 50 WFC3 50 phyllosilicate 50 whiz harmlessly 50 ESO telescopes 50 Advanced Synthetic Aperture 50 LORRI 50 GALEX 50 GOCE 50 Saturnian moons 50 magnetotail 50 detect gamma rays 50 Mars moon Phobos 50 Rover Opportunity 50 KBOs 50 Lunar Orbiter 50 Kepler Telescope 50 transiting exoplanet 50 Carina constellation 50 globular clusters 50 NASA Far Ultraviolet 50 particles WIMPs 50 meteoroid 50 BP Piscium 50 Keck Interferometer 50 Envisat satellite 50 Vostok 3KA 50 Mini SAR 50 Earthlike planets 50 Jonathan Lunine 50 Galilean moons 50 cosmic collisions 50 Stardust spacecraft swooped 50 Mars Lander 50 circumstellar disks 50 energetic electrons 50 Observatory SDO 50 Anisotropy Probe WMAP 50 Muons 50 Saturn Enceladus 49 LAGEOS 49 Kepler #b 49 planets orbiting distant 49 HIP #b 49 Upsilon Andromedae 49 Magellanic Stream 49 lowermost mantle 49 GJ#b 49 Kailash Sahu 49 Huygens Probe 49 Phaethon 49 Cassini orbiter 49 Lunar CRater Observation 49 infrared telescopes 49 geoneutrinos 49 Sagittarius B2 49 celestial sphere 49 NASA Mars Odyssey 49 Coma Cluster 49 V# Mon 49 Gerard Kuiper 49 spectroscopic measurements 49 polar craters 49 GQ Lupi 49 Red Planet 49 Descent Imager Spectral Radiometer 49 ionized gas 49 Cometary 49 CARTOSAT 49 outermost planets 49 orbiting Hubble Space Telescope 49 occultations 49 SIM PlanetQuest 49 Express orbiter 49 Steins asteroid 49 RS Ophiuchi 49 Mission TRMM satellite 49 intrinsic brightness 49 Spitzer Space Telescope 49 mu Arae 49 Trifid Nebula 49 chondritic meteorites 49 SIRTF 49 Noachian era 49 Martian meteorite 49 electrons orbiting 49 Science Experiment HiRISE 49 moon Charon 49 mineral olivine 49 highly elliptical orbit 49 chondrules 49 tholins 49 Phoenix Mars Lander 49 TrES 4 49 planetary Transits 49 Huygens probe 49 twin rover Opportunity 49 extrasolar planets 49 sized planets orbiting 49 antiquarks 49 Mars Opportunity rover 49 orbiting observatory 49 matter antimatter asymmetry 49 brown dwarf 49 neutrino 49 silicate rocks 49 comet Boethin 49 planets orbiting 49 infrared wavelengths 49 meteorites 49 meteorite fragments 49 astronomer Clyde Tombaugh 49 cosmological distances 49 MUSES C 49 protoplanet 49 planetary nebula 49 sun corona 49 microscopic imager 49 Gravitational waves 49 microquasar 49 NEOWISE 49 reionization 49 infrared spectrometers 49 Nasa Mars Odyssey 49 MARSIS 49 AB Aurigae 49 NASA Lunar CRater 49 Yinghuo 1 49 protons 49 particle physics detector 49 earliest tetrapods 49 protoplanetary 49 Atlantis undocks 49 magnetic reconnection 49 spectroscopically 49 distant quasars 49 NASA rover Spirit 49 submillimetre wavelengths 49 microlensing events 49 Lunar Crater Observation 49 Cosmic Microwave Background CMB 49 molten droplets 49 infalling 49 volcanic moon Io 49 arcsec 49 meteoritic material 49 Alycia Weinberger 49 Kepler observatory 49 filamentary structures 49 Boethin 49 WISE telescope 49 NASA Interstellar Boundary 49 Trojan asteroids 49 Gliese #e 49 reconnaissance orbiter 49 periodic dimming 49 Corot 9b 49 Rosetta comet chaser 49 Kuiper Belt Object 49 comet nuclei 49 Saturnian 49 blazar 49 lunar orbit 49 cosmic rays 49 Hale Bopp 49 AU Mic 49 mesosphere 49 arcsecond 49 jarosite 49 Analyzer TEGA 48 SINFONI 48 Galaxy Evolution 48 BLG #Lb 48 particle beam 48 moondust 48 chromosphere 48 orbiting Cassini spacecraft 48 spherules 48 AGNs 48 Mars Orbiter Camera 48 gamma rays emitted 48 planet Gliese #g 48 Jupiter moon Io 48 QQ# 48 asteroids comets 48 NASA Aqua 48 spectrographic 48 NASA Stardust NExT 48 Orionids 48 unmanned probes 48 SOHO spacecraft 48 transiting planet 48 solar neutrinos 48 spacecraft Chandrayaan 1 48 galactic cosmic rays 48 Mojzsis 48 LADEE 48 NFIRE satellite 48 planet HD #b 48 HiRISE image 48 Mars landers 48 Earthlike planet 48 cosmic ray particles 48 airglow 48 J# +# [002] 48 Ring Nebula 48 X ray observatory 48 Ringed Planet 48 Foton spacecraft 48 Kuiper belt objects 48 martian meteorites 48 interstellar dust tiny 48 cometary particles 48 Deep Impact mission 48 NASA Mars Orbiter 48 neutrinos 48 Alfvén waves 48 Jupiter moons 48 martian rocks 48 Mars Gusev Crater 48 Iapetus 48 ESO VLT 48 spacecraft thrusters 48 GJ #b [002] 48 Planck telescope 48 asteroid Lutetia 48 Philae lander 48 Comet Shoemaker Levy 48 CALIPSO 48 high temperature superconductivity 48 SpaceX Falcon 48 Late Heavy Bombardment 48 Milky Way Galaxy 48 planets Kepler 48 Andromeda galaxy 48 gravitational interactions 48 interstellar medium 48 Saturn equinox 48 retrograde orbit 48 carbonaceous chondrites 48 ULIRGs 48 highly elliptical orbits 48 NASA Solar Terrestrial 48 heavily cratered 48 High Resolution Imaging 48 miniature ovens 48 distant supernovas 48 Flyby spacecraft 48 Ocean Salinity 48 lunar poles 48 planet magnetosphere 48 silicate minerals 48 mission Chandrayaan 48 Interstellar Boundary Explorer 48 Lt. Col. Yang Liwei 48 faraway galaxies 48 ultraluminous galaxy 48 Cloud Aerosol Lidar 48 Syrtis Major 48 Microscopic Imager 48 Lapen 48 galaxy cluster 48 Aram Chaos 48 comets orbiting 48 apogee farthest point 48 Titan smoggy 48 asteroid collisions 48 supernova remnant 48 Gusev Crater 48 Ohmoto 48 neutron spectrometer 48 protoplanetary disks 48 CoRoT 9b 48 moons orbiting Saturn 48 ejecta blanket 48 femtoseconds 48 Omega Centauri 48 INSAT 4CR 48 Relations Observatory STEREO 48 thrilling stargazers 48 absorbs photons 48 Evolution Explorer 48 GPa 48 NASA Cosmic Background 48 Gliese #d 48 Envisat Advanced Synthetic Aperture 48 Io volcanoes 48 magnetospheric 48 Saturn magnetosphere 48 Hinode 48 shadowy craters 48 Cosmic Background Explorer 48 comet Hale Bopp 48 inhabitable planets 48 ultraviolet wavelengths 48 extrasolar 48 X ray emission 48 manned lunar mission 48 exoplanets 48 Bullet Cluster 48 Alfven waves 48 Zeta Ophiuchi 48 nucleobases 48 lunar orbits 48 SPICAM 48 Voyager probes 48 Martian terrain 48 flybys 48 cryovolcanism 48 IKAROS 48 elongated orbit 48 orbiting 48 exobiology 48 sols 48 CloudSat 48 gravitational waves 48 manned Shenzhou 48 HD# [002] 48 weakly interacting 48 Perseus Cluster 48 constellation Centaurus 48 detect gravitational waves 48 constellation Pegasus 48 spectroscopic analysis 48 Reflection Radiometer 48 asteroids Ceres 48 planet orbiting 48 Cassini ion 48 cometary debris 48 polar stratospheric 47 Herschel telescope 47 Gliese #c 47 X ray afterglow 47 nuclei 47 Context Camera 47 shepherding spacecraft 47 Cosmonaut Yuri Gagarin 47 neutrino particles 47 spacecraft 47 Michael A'Hearn 47 Mars rover Opportunity 47 constellation Eridanus 47 antimatter particles 47 silicates 47 Epsilon Aurigae 47 diffraction patterns 47 millisecond pulsars 47 Herschel Space 47 http:/www.nasa.gov/cassini 47 elongated orbits 47 Earth radii 47 heaviest payloads 47 Mars Color Imager 47 gaseous planets 47 Milky Way galaxy 47 ANI NASAs 47 radial velocity method 47 Upsilon Andromedae b 47 shadowed craters 47 Mars lander 47 visible wavelengths 47 olivine mineral 47 SMBHs 47 Imaging Spectroradiometer MODIS instrument 47 astrobiologists 47 sister rover Spirit 47 meteor impacts 47 Charon Pluto 47 Huygens lander 47 moon Io 47 LRO spacecraft 47 MN4 47 NEAR Shoemaker 47 Squyres Cornell 47 NanoSIMS 47 Halley Comet 47 muons 47 Quaoar 47 Martian plains 47 Haumea 47 binary asteroid 47 meteoroids 47 Higgs bosons 47 Kavoshgar 47 XMM Newton satellite 47 globular cluster 47 planets asteroids 47 KAGUYA 47 tau neutrino 47 orbits 47 NuSTAR 47 NASA Great Observatories 47 protostar 47 Mössbauer spectrometer 47 interacting galaxies 47 fainter objects 47 Evolved Gas 47 aboard Soyuz TMA 47 THEMIS spacecraft 47 Shenzhou IV 47 helium nuclei 47 olivine 47 isotopic compositions 47 NASA MESSENGER 47 simulated lunar 47 lander 47 Fomalhaut 47 orbiting gamma ray 47 Mars Orbiter Laser Altimeter 47 supersymmetric particles 47 Curiosity rover 47 exosolar planets 47 Wolszczan 47 ultracold atoms 47 Moderate Resolution 47 EGRET 47 electrons positrons 47 GOCE satellite 47 SNe Ia 47 CMB radiation 47 galactic clusters 47 ejecta plume 47 gamma ray flares 47 Imaging Spectroradiometer MODIS 47 NGC #A 47 cosmic dust 47 star Fomalhaut 47 GRB # 47 Comet Encke 47 spicules 47 aboard ESA Envisat 47 dwarf spheroidal 47 Eta Carinae 47 Cryosat 47 Bonneville Crater 47 aboard Vostok 47 SCISAT 47 ionised gas 47 interstellar dust clouds 47 X ray pulses 47 Supernova #A 47 Kuiper Belt Objects 47 Robotic Arm Camera 47 starburst galaxies 47 frozen sunless 47 Planetary Camera 2 47 Fermi Telescope 47 arcseconds 47 Hubble astronomers 47 galaxy clusters 47 goethite 47 Moessbauer spectrometer 47 Tempel Tuttle 47 Planetary Fourier Spectrometer PFS 47 Crab Nebula 47 supermassive black hole 47 keV 47 THEMIS probes 47 Comet McNaught 47 protostars 47 Cosmic Evolution 47 Kepler telescope 47 Odyssey orbiter 47 Galilean satellites 47 TNOs 47 pulsar 47 hydrated minerals 47 heliopause 47 Helix Nebula 47 rubidium vapor 47 moons orbiting 47 # Apophis 47 lunar crater 47 arctic plains 47 Cygnus Lyra region 47 accretion disk 47 redshifted 47 Characterization EPOCh 47 buckypaper virtually 47 Lyman alpha 47 OMEGA instrument 47 VLTI 47 situ measurements 47 Terra Meridiani 47 Martian permafrost 47 arcminutes 47 planet HD#b 47 biosignatures 47 sunlike stars 47 Cabeus 47 WIMPs 47 moon Mimas 47 Saturn moon Iapetus 47 Mars orbiter 47 AKARI 47 Jovian moons 47 comet Wirtanen 47 galaxy redshift 47 gravitational microlensing 47 HL Tau 47 backscattered 47 particle beams 47 spiral galaxy Messier 47 Sensing Satellite 47 Allende meteorite 47 SN #C 47 Andromeda Galaxy 47 Higgs boson particle 47 Astrological lore 47 NFIRE 47 inner Oort Cloud 47 spectral fingerprints 47 Hubble Space telescope 47 NASA rover Opportunity 47 regolith 47 cosmic ray collisions 47 Infrared Array Camera