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(Click for frequent words.) 75 Gusev crater 73 Meridiani Planum 66 Mars Gusev Crater 64 Martian equator 64 Opportunity rover 61 Martian surface 60 Meridiani 60 Mars Meridiani Planum 60 Bonneville Crater 59 rover Opportunity 59 rover Spirit 58 rover Spirit landed 58 layered bedrock 58 Martian crater 58 Meridiani plains 57 Martian arctic 57 Isidis Planitia 57 Victoria Crater 56 rock outcrop 56 NASA rovers Spirit 56 Endurance Crater 56 twin rover Opportunity 55 Syrtis Major 55 martian soil 55 Endurance crater 55 Endeavour Crater 55 Valles Marineris 55 vast Gusev Crater 55 Hellas Basin 55 Martian plains 55 six wheeled rover 55 polar craters 54 Orcus Patera 54 Arabia Terra 54 Martian landscape 54 Mars rover Opportunity 54 Vastitas Borealis 53 NASA Opportunity rover 53 Shackleton Crater 53 twin rover Spirit 53 nicknamed Bonneville 53 lunar equator 53 Saturn moon 53 Nili Fossae 53 Red Planet 53 martian 53 NASA Spirit rover 53 NASA Mars rover 53 Spirit rover 53 permanently shadowed craters 53 Martian polar 53 martian surface 52 hematite mineral 52 lunar craters 52 lunar crust 52 Elysium Planitia 52 Mars 52 Terra Meridiani 52 basaltic rocks 52 Martian arctic plains 52 Viking orbiters 51 Ontario Lacus 51 Ares Vallis 51 Shackleton crater 51 Lake Vostok 51 permanently shadowed 51 NASA rover Opportunity 51 Rover Spirit 51 scarps 51 moon permanently shadowed 51 Itokawa 51 shadowy craters 51 asteroid Itokawa 51 phyllosilicates 51 Hadley Rille 51 lunar surface 50 Venusian surface 50 Valles Marineris canyon 50 HiRISE image 50 Opportunity Mars rover 50 Cassini flyby 50 Martian craters 50 HiRISE camera 50 crater 50 NASA twin rovers 50 Viking Lander 50 Saturn Cassini 50 mineral olivine 50 called gray hematite 50 Orbiter MRO 50 ejecta blanket 50 Rover Opportunity 50 lander 49 Opportunity rovers 49 arctic plains 49 rover 49 spacecraft Cassini 49 mineralogical composition 49 volcano Olympus Mons 49 Kepler telescope 49 Martian terrain 49 sister rover Spirit 49 Oort Cloud 49 NASA Mars Reconnaissance 49 bedrock outcropping 49 Nasa spacecraft 49 Saturnian system 49 Mars CRISM 49 Sojourner rover 49 lunar crater 49 NASA rover Spirit 49 NASA rovers 49 icy moons 49 Martian soil 49 Cabeus crater 49 Steve Squyres 49 Hesperian Epoch 49 CoRoT satellite 49 Cabeus 49 Rover MER 49 rocky planets 49 Jupiter moons Europa 49 Mars rovers Spirit 49 gaseous planet 48 Mars Squyres 48 Huygens probe landed 48 orbiting Saturn 48 Olympus Mons 48 Mössbauer spectrometer 48 Orbiter LRO 48 Terra Sirenum 48 Taurus Littrow 48 Mars Reconnaissance Orbiter 48 Mini TES 48 GJ #b [001] 48 orbiting Mars 48 grabens 48 comet Wild 48 Jonathan Lunine 48 comet nucleus 48 Phoenix lander 48 robotic explorer 48 thermal emission spectrometer 48 Erebus Crater 48 Martian southern hemisphere 48 Galileo spacecraft 48 Martian rover 48 Comet Hartley 48 heavily cratered 48 Mercury flyby 48 PASADENA Calif. NASA 48 biosignatures 48 Lander robotic arm 48 Aram Chaos 47 equatorial plains 47 Mini SAR 47 Saturnian moon Titan 47 Antarctic Dry Valleys 47 Opportunity parachuted 47 Saturn moons 47 olivine mineral 47 robotic geologist 47 Oort cloud 47 WD5 47 Candor Chasma 47 COROT 7b 47 moon Titan 47 microscopic imager 47 Mawrth Vallis 47 Fomalhaut b 47 ESA Mars 47 TrES 4 47 Phoenix Mars Lander 47 Mars Odyssey orbiter 47 sedimentary deposits 47 magma ocean 47 Samuel Oschin Telescope 47 Mars Odyssey spacecraft 47 asteroid Eros 47 martian rocks 47 Martian 47 Moessbauer spectrometer 47 Solar Dynamics Observatory 47 LCROSS spacecraft 47 subsurface ocean 47 subglacial lake 47 Chasma Boreale 47 Comet Boethin 47 NASA Lunar Reconnaissance 47 OMEGA instrument 47 zodiacal light 47 spacecraft thrusters 47 jarosite 47 perchlorate salts 47 infrared telescope 47 Earth asteroid Itokawa 47 mantle plumes 47 polygon shaped 47 Hesperian epoch 47 NASA Cassini spacecraft 47 Ranging spacecraft 47 asteroid Vesta 47 Messenger spacecraft 47 abyssal plains 47 gray hematite 47 martian landscape 47 lobate scarps 47 heliosheath 47 sulfate salts 47 rovers Spirit 46 twin rovers Spirit 46 Explorer WISE 46 lunar poles 46 Viking landers 46 planets orbiting sun 46 Gakkel Ridge 46 KBOs 46 hydrated minerals 46 smoothest flattest spot 46 laser altimeter 46 galaxy M# [002] 46 Mössbauer 46 Nasa Mars Reconnaissance 46 cinder cones 46 Jupiter icy moons 46 Saturn moon Enceladus 46 Upsilon Andromedae b 46 interstellar dust grains 46 Itokawa asteroid 46 lander robotic arm 46 Manned missions 46 comet Churyumov Gerasimenko 46 Microscopic Imager 46 Chicxulub crater 46 northern arctic plains 46 Compact Reconnaissance Imaging Spectrometer 46 NASA Cassini 46 Apollo missions 46 Lunar Reconnaissance Orbiter LRO 46 Kepler spacecraft 46 unmanned probes 46 telescopic observations 46 Kraken Mare 46 Saturn moon Mimas 46 CoRoT 7b 46 icy comets 46 thin crescent 46 Odyssey orbiter 46 lunar soil 46 planet Gliese #g 46 polygon patterns 46 ejecta plume 46 Arsia Mons 46 Tharsis Rise 46 NASA Stardust spacecraft 46 planets orbiting 46 orbiting spacecraft 45 permanently shadowed crater 45 Hellas Planitia 45 planets astronomers 45 meteorite fragments 45 THEMIS Images 45 super perigee moon 45 Mars northern latitudes 45 lunar regolith 45 Earth asteroids 45 Mars rover Spirit 45 Earthlike planets 45 constellation Eridanus 45 Jupiter Ganymede 45 Mars Exploration 45 Moon Mineralogy Mapper 45 Kuiper Belt 45 circumstellar disk 45 spherules 45 waning crescent 45 gray hematite mineral 45 Mars rovers Opportunity 45 MARSIS 45 shadowed craters 45 Chryse Planitia 45 solidified lava flows 45 rover robotic arm 45 Curiosity rover 45 Stardust capsule 45 Diviner 45 slender crescent 45 Kepler Telescope 45 Mars Reconnaissance Orbiter MRO 45 Mazatzal 45 Diviner instrument 45 Mars Opportunity rover 45 CRISM 45 Hematite Slope 45 Mars Orbiter Camera 45 constellation Virgo 45 polar vortex 45 Sensing Satellite LCROSS 45 Martian meteorite 45 Ithaca Chasma 45 Dry Valleys 45 Context Camera 45 lunar perigee 45 MESSENGER spacecraft 45 Caloris Basin 45 Reconnaissance Orbiter 45 Mossbauer spectrometer 45 Ius Chasma 45 Upsilon Andromedae 45 polar layered 45 orbiting Kepler telescope 45 constellation Carina 45 asteroid Steins 45 Ground penetrating radar 45 Ulysses spacecraft 45 Martian rovers 45 GJ#b 45 KT boundary 45 metamorphic rock 45 Saturn Enceladus 45 EPOXI mission 45 lunar highlands 45 filamentary structures 45 fissure eruption 45 Cancri e 45 NASA Mars Orbiter 45 continental crust 45 basalt volcanic 45 Kuiper belt 45 Lunar Reconnaissance Orbiter 45 photosphere 45 Herschel Space Telescope 45 robotic rovers 45 Cryogenian period 45 lunar orbiters 45 stationary lander 45 smoothest flattest 45 lensing galaxy 45 Martian dust 44 inner asteroid belt 44 Sensing Satellite 44 innermost planet 44 Spirit Mars rover 44 Pancam 44 mesosphere 44 Racetrack Playa 44 APXS 44 Caloris 44 NASA Voyager spacecraft 44 icy crust 44 Lunokhod 44 protoplanet 44 Jeffrey Plaut 44 rock abrasion 44 retroreflector 44 Martian crust 44 Phobos 44 Cassini flybys 44 Clementine spacecraft 44 Epoxi 44 simulated lunar 44 Son Nghiem 44 rovers 44 Global Surveyor 44 ancient lakebed 44 celestial sphere 44 Huygens descent 44 HiRISE images 44 Virgo Cluster 44 ferric oxides 44 Cosmic Background Explorer 44 #P/Churyumov-Gerasimenko 44 spacecraft flyby 44 Lunar Prospector 44 ejecta 44 Titan flyby 44 NEAs 44 GJ #b [002] 44 jagged ridge 44 comets orbiting 44 ESA Huygens probe 44 smallest exoplanet 44 Mount Bosavi 44 hematite 44 lunar meteorites 44 Mars Orbiter 44 subglacial lakes 44 Martian volcanoes 44 waxing gibbous 44 comet flyby 44 Jupiter flyby 44 moon Europa 44 Gamburtsev 44 NASA Interstellar Boundary 44 Di Achille 44 Wassuk Range 44 Mars Pathfinder 44 # Apophis 44 solidified lava 44 glacially carved 44 Thermal Emission Spectrometer 44 rover Sojourner 44 Titan Saturn 44 Milky Way Galaxy 44 Voyager spacecraft 44 mineral hematite 44 equatorial regions 44 IBEX spacecraft 44 comet Boethin 44 Noachian era 44 Tarantula Nebula 44 GA6 44 Siberian Traps 44 NASA Kepler spacecraft 44 THEMIS satellites 44 wrinkle ridges 44 LCROSS mission 44 WISE telescope 44 concretions 44 twin rovers 44 HiRISE 44 Stardust spacecraft 44 planemos 44 melt inclusions 44 moon Enceladus 44 comet nuclei 44 journal Meteoritics 44 Martian gullies 44 unmanned rover 44 exoplanets orbiting 44 Huygens 44 permanently shadowed lunar 44 Yellowstone caldera 44 Ocean Salinity SMOS 44 lunar orbits 44 Kepler #b 44 Chandrayaan 44 planets asteroids 44 MG J# +# 44 Orionids 44 moons Phobos 44 Planitia 44 retrograde orbit 44 magmas 44 Comet #P/Churyumov-Gerasimenko 44 exoplanetary systems 44 moonquakes 44 Iapetus 43 ray Space Telescope 43 Mars Color Imager 43 closest flyby 43 comets asteroids 43 cometary dust 43 tidal bulge 43 Cygnus Lyra region 43 distant supernovae 43 Quaoar 43 called lobate scarps 43 Fermi telescope 43 DISR 43 wheeled rovers 43 Perseus Cluster 43 MARSIS radar 43 Michael Studinger 43 carbonaceous chondrite 43 Redoubt blew 43 phyllosilicate 43 lava tubes 43 airglow 43 sedimentary rock 43 Zeta Ophiuchi 43 protoplanetary disk 43 GRB #B 43 Comet Tempel 1 43 Taurus Littrow Valley 43 Kuiper belt objects 43 NASA Mars Odyssey 43 Asteroid Itokawa 43 silicic 43 Cat Paw Nebula 43 Landsat satellite 43 seafloors 43 martian meteorites 43 Spaceguard 43 igneous rocks 43 Galaxy Evolution 43 Shenzhou IV 43 Herschel telescope 43 ecliptic plane 43 AU Mic 43 Mission SRTM 43 finely layered 43 layered outcrops 43 McMurdo Dry Valleys 43 smoggy atmosphere 43 mineralized outcrops 43 rock outcropping 43 EPOXI 43 Squyres Cornell 43 EPOXI spacecraft 43 steam eruptions 43 moon Phobos 43 planets orbits 43 Huygens probe 43 penumbral shadow 43 smallest exoplanets 43 Comet Tempel Tuttle 43 constellation Ursa Major 43 Comet Lulin 43 Heliospheric Observatory SOHO 43 Corot 7b 43 Gerard Kuiper 43 Earth asteroids NEAs 43 Tranquility Base 43 basalts 43 field Infrared Survey 43 shaded craters 43 manager Jennifer Trosper 43 Murchison meteorite 43 penetrating radar 43 NASA MESSENGER spacecraft 43 cometary 43 equatorial latitudes 43 ultramafic intrusives 43 Planck satellite 43 turbidites 43 NASA Lunar Crater 43 Churyumov Gerasimenko 43 Cassini spacecraft 43 Mars landers 43 NASA Lunar Prospector 43 Charon Pluto 43 active volcanism 43 brecciated silicified 43 New Horizons spacecraft 43 Meteor Crater 43 extrasolar 43 Cassini Huygens spacecraft 43 HiRISE camera aboard 43 interstellar boundary 43 Squyres 43 robotic rover Spirit 43 Comet Machholz 43 Mars orbiting spacecraft 43 Ringed Planet 43 SHARAD 43 earthlike planets 43 meteoroid 43 WISE spacecraft 43 landforms 43 NASA LCROSS 43 shadowed crater 43 RQ# 43 Martian meteorites 43 meteor impacts 43 craters 43 gaseous planets 43 noctilucent clouds 43 interstellar dust particles 43 Opportunity Mars rovers 43 Epsilon Eridani 43 planet Uranus 42 Laurentide Ice Sheet 42 Henize #-# 42 Petermann Glacier 42 outcropping 42 onboard Chandrayaan 42 Sedna 42 extinct volcanoes 42 Descent Imager Spectral Radiometer 42 manager Pete Theisinger 42 P/# A2 42 ALH# 42 WASP #b 42 Planetary Fourier Spectrometer PFS 42 cluster NGC 42 reconnaissance orbiter 42 magma chambers 42 robotic spacecraft 42 planets orbiting distant 42 gravitational lenses 42 fault scarps 42 geologically active 42 Mars Lander 42 Huygens lander 42 observable universe 42 Asteroid Belt 42 hydrothermal vent 42 Mars Pathfinder lander 42 ESA ASI 42 permanently shadowed regions 42 orbiting observatories 42 occultations 42 Kanaga Volcano 42 Orbiter 42 constellation Cygnus 42 meteoritic material 42 Goldilocks planet 42 Enceladus 42 constellation Scorpius 42 Bruce Jakosky 42 exobiology 42 Mars Phobos 42 Earth ionosphere 42 Regolith 42 Martin Tomasko 42 impactor spacecraft 42 solar nebula 42 Wilkinson Microwave Probe 42 Tharsis 42 crossbedding 42 Planck observatory 42 Gliese #g 42 planets Uranus 42 Oceanus Procellarum 42 galactic mergers 42 Kuiper Belt objects 42 Mars moon Phobos 42 Galilean satellites 42 NASA Kepler 42 Andromeda galaxy 42 Rock Abrasion Tool 42 Martian rocks 42 dimensional atlas 42 habitable zones 42 Mini Thermal Emission 42 GOCE satellite 42 Venusian atmosphere 42 interstellar dust samples 42 Saturn moon Iapetus 42 moons Europa 42 Kuiper Belt object 42 interstellar cloud 42 Flyby spacecraft 42 lunar magma 42 Interior Laboratory GRAIL 42 planetary geologists 42 outcrop 42 Kilauea summit 42 treeless expanse 42 outer corona 42 transiting exoplanet 42 Nasa Kepler 42 SIRTF 42 gamma ray observatory 42 exoplanetary 42 impactor 42 Jovian moon 42 Phoebe orbits 42 ChemCam 42 Epsilon Aurigae 42 comet dust 42 Chicxulub Crater 42 geologic 42 STSS Demo 42 moon 42 spacecraft 42 infrared spectrometer 42 John Grotzinger 42 smallest extrasolar planet 42 Ken Herkenhoff 42 Pluto Charon 42 THEMIS Image 42 Quadrantid meteor shower 42 Bramley Murton 42 ionized gas 42 Ranging MESSENGER spacecraft 42 sols 42 meteorite bombardment 42 evaporite deposits 42 caldera 42 HD#b 42 Cassini Huygens 42 Herschel Crater 42 Fra Mauro 42 Horizons spacecraft 42 moon Mimas 42 Saturn rings 42 Comet Hartley 2 42 carbonate minerals 42 Kepler Mission 42 NASA EPOXI mission 42 Deep Impact flyby spacecraft 42 waxing crescent 42 robotic arm 42 sunlike star 42 Purgatory Dune 42 Lutetia 42 BP Piscium 42 orbiting Mars Odyssey 42 lava tube 42 Cassini orbiter 42 Mars Global Surveyor 42 abyssal plain 42 probe Huygens 42 Lunar Crater 42 Lake Cheko 42 Comet 9P/Tempel 1 42 Centaur rocket 42 Caloris basin 42 Hubble Ultra 42 Larry Soderblom 42 basaltic 42 comet Hartley 2 42 Huygens Probe 42 Boar Tusk 42 Comet Halley 42 planets orbiting stars 42 Melas Chasma 42 martian atmosphere 42 Mars Odyssey 42 asteroids orbiting 42 gamma ray spectrometer 42 Antarctic meteorites 42 ESA SMART 42 Jupiter moon Io 41 Rosetta spacecraft 41 Kazakhstan steppe 41 iron meteorite 41 penumbral eclipse 41 WISE mapped 41 tiny meteoroids 41 basaltic rock 41 lunar 41 habitable planets 41 spiral galaxy NGC 41 Borealis basin 41 spacecraft Chandrayaan 1 41 cosmic collisions 41 Comet Holmes 41 NASA THEMIS 41 QQ# 41 Pleiades cluster 41 Alfred McEwen 41 explosive volcanism 41 NASA Kepler telescope 41 durable twin rovers 41 Noctilucent clouds 41 flyby spacecraft 41 Coma Cluster 41 hydroxyl molecules 41 Jet Propulsion Laboratory JPL 41 landers 41 extrasolar planets 41 Sojourner Rover 41 robot rovers 41 trench informally 41 Lunar CRater Observation 41 exosphere 41 Kounaves 41 lunar orbit 41 crater rim 41 Kepler Space Telescope 41 Orientale Basin 41 Okmok Caldera 41 outer planets 41 thin crescent moon 41 Trifid Nebula 41 Nikumaroro 41 ringed planet 41 comet #P/Churyumov-Gerasimenko 41 constellation Aquarius 41 cosmic magnifying glass 41 Laurentide ice sheet 41 Rosetta lander 41 cosmological distances 41 comet Tempel 1 41 Ares IX rocket 41 spacecraft orbiting 41 potentially habitable 41 stony meteorites 41 habitable worlds 41 Cassini 41 Climate Experiment GRACE 41 Submillimeter Array 41 Orion nebula 41 rock outcrops 41 Infrared Pathfinder Satellite 41 look distractingly cartoony 41 Comet Hale Bopp 41 Ruined Castle 41 Bruce Banerdt 41 yardangs 41 tektites 41 arcsecond 41 interstellar molecules 41 planetary surfaces 41 gibbous moon 41 axial tilt 41 Lunar Reconnaissance Orbiter Camera 41 constellation Taurus 41 radar altimetry 41 COROT 41 Fossett vanished 41 meteor craters 41 Jean Pierre Bibring 41 Kuiper Belt Objects 41 extrasolar planet 41 astrobiologists 41 Earth magnetosphere 41 Perseid Meteor Shower 41 weather satellite TIROS 41 Today waxing Virgo 41 cometary material 41 planet HD #b 41 southern supercontinent 41 substorm 41 whiz harmlessly 41 YORP effect 41 Mars Rover 41 magnetosphere 41 infrared telescopes 41 meteorite craters 41 twin Voyager spacecraft 41 Opportunity 41 Wilkinson Microwave Anisotropy Probe 41 Robotic Arm Camera 41 stromatolite 41 moon Deimos 41 volcanism 41 zircon crystals 41 Lake Untersee 41 filamentary structure 41 massifs 41 chondritic meteorites 41 plucky rover 41 exo planets 41 SIM PlanetQuest 41 twin Viking landers 41 moon Io 41 silicates 41 Deep Impact eXtended Investigation 41 Dodo Goldilocks 41 cometary debris 41 silicate mantle 41 constellation Cassiopeia 41 Io Europa 41 igneous rock 41 Comet Encke 41 radial velocity 41 hydrosphere 41 Omega Centauri 41 Nikku Madhusudhan 41 orbital eccentricity 41 Foton M3 41 motorized rasp 41 total odometry 41 basalt rocks 41 reentry capsule 41 dust devils 41 Snowball Earth 41 moons orbiting 41 STEREO mission 41 neutral mass spectrometer 41 Cerro Pachon 41 KAGUYA 41 ICESat 41 magnetotail 41 Martian atmosphere 41 Mars Orbiter Laser Altimeter 41 navigate autonomously 41 circular orbit 41 gullies 41 frigid polar 41 mastodon tusk 41 Herschel Space 41 moons orbiting Saturn 41 wheeled robot 41 sub glacial lakes 41 star Spica 40 Cosmic Microwave Background 40 Deep Impact craft 40 Space Telescope GLAST 40 extrasolar planetary systems 40 ionized hydrogen 40 GRACE satellites 40 pyroclastics 40 barren moonscape 40 Horsehead Nebula 40 Eagle Nebula 40 Milky Way galaxy 40 Andaman Islands quake 40 magma dome 40 OSIRIS REx 40 mission Chandrayaan 40 Lyrid meteor shower 40 chromosphere 40 BP Psc 40 astrobiological 40 Space ENvironment GEochemistry 40 robotic rover 40 Earthlike 40 impactors 40 primitive meteorites 40 Ed Weiler NASA 40 Cosmic Evolution 40 carbonaceous chondrites 40 VY Canis Majoris 40 Nisqually Glacier 40 Polar Lander 40 asteroidal 40 Deep Impact mission 40 UB# Xena 40 Carina constellation 40 Shepherding Spacecraft 40 planetary explorations 40 comet 40 robotic geologists 40 Martian permafrost 40 WMAP satellite 40 exoplanet orbiting 40 Soyuz Fregat rocket 40 asteroid 40 AB Aurigae 40 Earthlike planet 40 volcanic lava flows 40 magma chamber 40 YU# 40 Space Environment Geochemistry 40 Solar TErrestrial RElations Observatory 40 heliosphere 40 Martian winters 40 Space Infrared Telescope 40 Chairman G Madhavan 40 mere fly bys 40 orbiter Mars Odyssey 40 Huygens mission 40 large oceanic plateaus 40 calderas 40 globular cluster 40 Envisat satellite 40 Red Rectangle 40 comet McNaught 40 Japan Hayabusa spacecraft 40 robotic lander 40 orbiting observatory 40 Gliese #c 40 Molten rock 40 Mercury magnetosphere 40 Evolution Explorer 40 spokesman Michael Braukus 40 Neutron Detector 40 Lunar Orbiter 40 Moon Mineralogy Mapper M3 40 Mars rovers 40 orbiter 40 Solar System 40 NuSTAR 40 aperture telescope 40 Foton M3 spacecraft 40 undersea volcanoes 40 outcrops 40 periodic dimming 40 cosmic microwave background 40 Steven Squyres 40 vugs 40 cosmic microwave radiation 40 cratered highlands 40 circular orbits 40 magnetic polarity 40 proto planetary disks 40 moon Mab 40 NASA Gamma ray 40 NROL 40 NASA ICESat 40 Tunguska asteroid 40 Pluto Kuiper Belt 40 HD #b [002] 40 Hale Bopp 40 prebiotic molecules 40 planet Gliese #c 40 panoramic camera 40 Soil Moisture 40 Milky Way 40 basalt flows 40 scientist Anthony Colaprete 40 geosynchronous orbit 40 Fuk Li Mars 40 Saturn magnetosphere 40 Gamma ray Large 40 Hubble orbits 40 Martian orbit 40 CryoSat mission 40 volcanic vents 40 laboratory Skylab 40 Orion Nebula 40 Eta Aquarid meteor shower 40 Perseus constellation 40 giant gaseous planets 40 Viking Orbiter 40 Analyzer TEGA 40 northern latitudes 40 telescopes astronomers 40 luminous galaxies 40 director Charles Elachi 40 Ring Nebula 40 Beardmore Glacier 40 Beta Pictoris b 40 seafloor sediments