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Loading contentNASA's Astrophysics Data System, the digital library of astronomy — indexing essentially the entire research literature and linking every paper to the data, catalogues, and objects it uses, so the literature and the data are one connected web.
Facts on this topic will be cited from these primary and reference sources.
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.