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Loading contentEvery grounded answer carries the provenance of the entities it draws on — the sources cited on each, and the review status of the knowledge — so the reader can weigh how far to trust it. No answer without its provenance.
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.