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Dwarf planets are observed by the sunlight they reflect. Undiscovered dwarf planets at the outer boundaries of our solar system are simply fainter than the other things mentioned. If they can't be seen then they can't be discovered. It is possible that they are just about bright enough to be seen but even then, in a single picture they are indistinguishable ...


6

All bright enough dwarf planets in the vicinity of the Sun have already been discovered, for all others only the Keck observatory in Hawaii is able to discover any. Once the Vera Rubin observatory goes into service, it will be able to recognize almost all (dwarf) planets beyond Eris through one double survey of a huge area of the sky.


5

distant galaxies and clusters, locate supermassive black holes Galaxies and clusters are very bright objects. That's intuitive: galaxies contain a lot of stars, each of which are roughly as luminous as our sun. Clusters consist of galaxies, so they are naturally even brighter. A faraway object that's very bright is naturally easier to detect than a close ...


2

Yes. There is no reason why one wouldn't. But we don't know any exo-dwarf planets (yet). See the answer to this question why.


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