Related by context. Frequent words. (Click for all words.) 58 planetary nebulae 58 comets 57 planetesimals 57 interstellar dust 57 cometary 56 comet dust 56 lunar soil 56 dwarf galaxies 55 Earthlike 55 meteoroids 55 magnetars 55 Kuiper Belt objects 55 protoplanetary disk 55 NASA Stardust spacecraft 54 globular clusters 54 Galaxy Evolution 54 Saturn rings 54 comet 54 Voyager spacecraft 54 NASA ESA Hubble 54 meteorites 54 Oort Cloud 54 regolith 54 organic molecules 53 igneous rocks 53 methanogens 53 Martian rocks 53 lavas 53 circular orbits 53 astrobiologists 53 moonlets 53 terrestrial planets 53 Martian landscape 52 Kuiper belt 52 amino acid sequences 52 moon Europa 52 lava tubes 52 spectral signatures 52 spherules 52 XMM Newton 52 silicates 52 rocky planets 52 biological molecules 52 Saturn moons 52 morphologies 52 comet nucleus 52 microfossils 51 astronomical objects 51 baryons 51 galaxy formation 51 comet Wild 51 nanosized 51 volcanic vents 51 planets circling 51 distant galaxies 51 zircons 51 olivine 51 hot Jupiters 51 comet tail 51 oxygen isotopes 51 elliptical galaxies 51 Stardust spacecraft 50 supernova remnants 50 nanodiamonds 50 extrasolar planet 50 infrared spectroscopy 50 planetary nebula 50 aerosol particles 50 trilobites 50 planets 50 active galactic nuclei 50 martian soil 50 spectroscopic 50 supernova explosions 50 outer planets 50 Hubble observations 50 nanoscopic 50 Galileo spacecraft 50 supernova explosion 50 solar nebula 50 Cosmic rays 50 super Earths 50 stromatolites 49 ribonucleic acid RNA 49 WASP #b 49 Gamma rays 49 placental mammals 49 Spitzer Space Telescope 49 elemental composition 49 morphologically 49 melanosomes 49 NASA Cassini 49 Saturn moon 49 dwarf galaxy 49 spectrographs 49 nebulae 49 magmas 49 micelles 49 innermost planet 49 solar corona 49 microlensing