Related by context. Frequent words. (Click for all words.) 42 Pluto 39 exoplanet 38 planets orbiting 38 planetary scientist 38 extrasolar planets 36 orbiting 36 exoplanets 36 Carl Sagan 36 orbits 36 planets 35 planet orbiting 35 fainter 34 rocky planets 34 astronomer 34 Solar System 34 Milky Way galaxy 33 brown dwarf 33 Uranus 33 orbited 33 suns 32 astronomers 32 Astronomers 31 quasars 31 galaxy 31 nebulae 31 Gliese 31 MESSENGER 31 galaxies 31 supernova 31 Saturn moon 31 vent 31 astrophysicists 31 Beagle 31 neutron star 31 celestial objects 30 neutrinos 30 planetary 30 brown dwarfs 30 Mars rovers 30 Mars 30 pulsar 30 Milky Way 29 Charon 29 Earthlings 29 nebula 29 dwarf planet 29 moons 29 dwarf galaxies 29 UB# [003] 29 quasar 29 Saturn rings 29 Cassini 29 universe 29 Sedna 29 moon Titan 29 elliptical orbit 29 gamma ray burst 29 galactic 29 interstellar space 29 Planck 29 Enceladus 28 Earth 28 Kepler 28 Halley Comet 28 Martian 28 supernovas 28 orbit 28 Earth orbit 28 planet 28 Planets 27 galaxy clusters 27 supernovae 27 cosmic 27 Asteroid 27 Universe 27 Red Planet 27 interplanetary 27 cosmic ray 27 asteroid 27 distant galaxies 27 transits 26 celestial bodies 26 comets 26 Xena 26 Phobos 26 Io 26 moon 26 asteroids 26 redshift 26 International Astronomical 26 solar flares 25 habitable zone 25 Hubble Space Telescope 25 venting 25 rants 25 Hubble telescope 25 Earths 25 neutrino 25 Jupiter 25 Hubble Telescope 25 celestial