Related by context. Frequent words. (Click for all words.) 67 supernova explosion 57 comets 55 mass extinctions 55 solar flares 54 glaciation 53 volcanism 53 cosmic ray 53 supernovae 53 gamma ray burst 53 radioactive decay 52 cometary 52 meteorites 52 quasars 52 asteroid 51 globular clusters 51 outer planets 51 volcanic eruptions 51 comet 51 Kuiper Belt 50 impactor 50 asteroids 50 magnetosphere 50 supernova 50 Little Ice Age 50 dwarf galaxies 50 Big Bang 50 supernovas 50 mass extinction 49 CMEs 49 elliptical galaxies 49 planets 49 plate tectonics 48 cosmic microwave background 48 rocky planets 48 Itokawa 48 olivine 48 distant galaxy 48 galaxy cluster 48 comet Wild 48 cosmic radiation 48 cosmic rays 48 neutron stars 48 Precambrian 48 galaxy clusters 47 galaxies 47 Saturn rings 47 interstellar dust 47 Solar System 47 neutron star 47 asteroid belt 47 organic molecules 47 meteorite 46 Tunguska 46 XMM Newton 46 quasar 46 oscillations 46 gamma ray bursts 46 WMAP 46 single celled organisms 46 brown dwarfs 46 sunspot 46 Martian atmosphere 46 crustal 46 planets orbiting 46 Pliocene 45 gamma rays 45 nuclei 45 protons 45 martian 45 NASA Chandra 45 orbits 45 extrasolar planets 45 interstellar medium 45 pulsars 45 meteor 45 eruptions 45 laser pulses 45 astronomers 45 Iapetus 45 distant galaxies 45 meteors 45 planetary 45 atmospheric circulation 44 GRB 44 cosmologists 44 Martian surface 44 HD #b [002] 44 mid latitudes 44 astrophysical 44 pyroclastic flows 44 geomagnetic field 44 Martian 44 galaxy 44 brown dwarf 44 sunspots 44 dynamical 44 neutrino 44 Milky Way Galaxy 44 magnetic fields 44 supermassive black holes 44 exoplanets