Related by context. Frequent words. (Click for all words.) 65 Tombaugh 51 astronomers 49 Pluto 49 astronomer 48 Lowell Observatory 47 dwarf planet 47 UB# [003] 46 planet orbiting 46 extrasolar planet 45 astrophysicist 45 HD #b [002] 44 astrophysicists 44 Carl Sagan 44 exoplanet 44 Halley Comet 43 Itokawa 43 asteroid 43 amateur astronomer 43 physicists 43 meteorite 43 Astrophysical Journal 42 Astronomers 42 WM Keck Observatory 42 astronomy 42 Spitzer Space Telescope 42 UFO sighting 41 distant galaxy 41 XMM Newton 41 extrasolar planets 41 brown dwarf 41 cosmologist 41 Astrophysical Journal Letters 41 NASA Cassini spacecraft 41 planets orbiting 41 amateur astronomers 41 Sedna 40 UFO 40 orbited 40 paleontologists 40 Orion Nebula 40 comet dust 40 Pleiades 40 cosmologists 40 Saturn rings 40 physicist 40 meteorites 40 Copernicus 40 Cassini spacecraft 39 X ray Observatory 39 Eta Carinae 39 code talkers 39 NASA Chandra 39 orbiting 39 skywatchers 39 ringed planet 39 comet Wild 39 discoverer 39 Johannes Kepler 39 Space Telescope 39 Apollo astronauts 39 Ernie Pyle 38 comet 38 Ophiuchus 38 geologically active 38 Very Large Telescope 38 astrobiology 38 Perseid meteor shower 38 exoplanets 38 Phoenix lander 38 Astronomical Society 38 Christa McAuliffe backup 38 chupacabra 38 planetary science 38 rocky planets 38 Meridiani Planum 38 Astronomer 38 moon Titan 38 International Astronomical 38 astrobiologist 38 WMAP 38 meteor 38 extraterrestrials 38 von Braun 38 Hubble telescope 38 cosmic microwave background 38 Hubble Space Telescope 38 palaeontologists 37 scientists 37 brown dwarfs 37 Royal Astronomical Society 37 moons 37 Physicists 37 UFOs 37 planetary scientist 37 planets 37 Kepler 37 Milky Way Galaxy 37 shuttle disintegrated 37 gamma ray burst 37 interstellar dust 37 unmanned spacecraft