Related by context. Frequent words. (Click for all words.) 64 martian soil 62 Martian rocks 62 lunar soil 61 spherules 61 Martian dust 60 Martian landscape 59 icy moons 59 icy crust 59 Lake Vostok 59 NASA Opportunity rover 58 Meridiani 58 rock outcrop 58 Opportunity rover 58 NASA Spirit rover 57 Martian surface 56 snail shells 56 salt crystals 56 comet dust 56 martian surface 56 Martian equator 56 Martian soil 56 Mars rover Opportunity 56 Endurance Crater 56 exosphere 55 striations 55 microscopic imager 55 moon Enceladus 55 lava tubes 55 scarps 55 Titan Saturn 54 outer crust 54 Saturn moon 54 chalky white 54 martian 54 martian atmosphere 53 craters 53 rocks 53 moon Europa 53 microfossils 53 Earthlike 53 undersea volcanoes 53 regolith 53 foraminifera 53 heavily cratered 53 Valles Marineris 53 meteorite impacts 53 crust 53 Cabeus crater 53 moonlets 53 igneous rocks 53 Galileo spacecraft 53 alternating layers 53 rover Spirit 53 planetesimals 53 rock outcrops 53 Martian arctic 53 igneous rock 53 volcanic vents 52 elemental composition 52 Meridiani Planum 52 Voyager spacecraft 52 surface 52 hardened lava 52 Mars rovers Spirit 52 hollow tubes 52 Viking landers 52 ejecta 52 gaseous planets 52 lake sediments 52 clasts 51 landforms 51 nanobubbles 51 photosphere 51 mussel shells 51 meteoroids 51 dust devils 51 spectral signatures 51 polar vortex 51 stalagmites 51 rover Opportunity 51 cometary 51 moon Titan 51 Saturn rings 51 oxygen isotopes 51 Saturn moon Enceladus 51 oceanic crust 51 steam vents 50 sedimentary rock 50 protoplanetary disk 50 corrugations 50 glacial till 50 Olympus Mons 50 nanosized 50 comet nucleus 50 zircons 50 boron nitride 50 stromatolites 50 coarse sand 50 asteroids 50 Siberian permafrost 50 astrobiologists