Related by context. Frequent words. (Click for all words.) 71 Earth 68 earth 64 planetary 63 galaxy 63 planets 62 universe 61 cosmos 60 oceans 59 mankind 59 humankind 57 Earths 56 biosphere 54 Red Planet 54 Martian surface 54 continent 53 Planet Earth 52 galactic 52 world 52 comet 52 Solar System 51 asteroids 51 Uranus 50 polar regions 50 moon 50 exoplanet 50 Milky Way galaxy 50 moons 50 asteroid 50 cosmic 49 Mars 49 outer space 49 lunar surface 49 humanity 49 exoplanets 49 Mother Earth 49 globe 48 Universe 48 Martian 48 intergalactic 48 Enceladus 48 beings 47 mass extinction 47 interstellar 47 ozone layer 47 orbiting 47 asteroid belt 46 galaxies 46 interplanetary 46 equator 46 supernova 46 comets 46 distant galaxies 46 celestial bodies 46 civilization 46 Milky Way 45 extraterrestrial 45 Saturn moon 44 Martian atmosphere 44 orb 44 Kuiper Belt 44 sentient 44 solar flares 44 dwarf planet 44 global warming 44 neutron star 43 Antarctica 43 Pluto 43 orbits 43 creatures 43 ocean 43 human beings 43 Hubble telescope 42 polar ice 42 Saturn rings 42 gamma ray bursts 42 alien 42 Earth orbit 42 celestial 42 cosmic rays 42 supernovae 42 starship 42 pulsars 42 nebula 41 hemisphere 41 universes 41 pulsar 41 suns 41 spacecraft 41 ecosystems 41 polar 41 Planet 41 humans 41 Amazon rainforest 41 western hemisphere 40 Global warming 40 marine ecosystems 40 tropics 40 aliens 40 civilizations 40 sunspot 40 Spitzer Space Telescope