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Astronomy

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    $\begingroup$ They're also moving extremely slowly. $\endgroup$
    – PM 2Ring
    Commented Jun 20, 2021 at 19:45
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    $\begingroup$ @PM2Ring but faster than stars and with a very big parallax. $\endgroup$
    – ProfRob
    Commented Jun 20, 2021 at 21:16
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    $\begingroup$ Also worth noting (though this wasn't part of the question) that the reason we can detect planets outside the solar system when we don't know about all the ones inside it is that those extra-solar planets are generally detected via either a wobble in the movement or transit of their parent stars, which obviously wouldn't apply for detecting things around our own star, since any wobble from such small, distant dwarf planets would be too small to be measurable, and they'd have to be between us and the Sun for a transit, and we'd definitely know about those. $\endgroup$
    – Darrel Hoffman
    Commented Jun 21, 2021 at 14:30
  • $\begingroup$ @DarrelHoffman indeed, and there is a question about that somewhere in Astonomy SE. $\endgroup$
    – ProfRob
    Commented Jun 21, 2021 at 15:13
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    $\begingroup$ Also worth noting that Pluto, despite being discovered in the area where something was expected to be found to account for disturbances in the orbit of Uranus, was photographed at least 15 times between 1909 and 1930 without anyone noticing it. $\endgroup$
    – chepner
    Commented Jun 21, 2021 at 18:48