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Thread: Plausible dates of discovery and disproving

  1. #1
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    Plausible dates of discovery and disproving - counter-earths and hypothetical planets

    I sketched out a draft of a sci-fi story which concerned a hypothetical planet in the solar system. The inspiration was the 1940 version of Superman, where Krypton was a counter Earth in the L3 Lagrange point (the one on the far side of the sun). In 1940, the existence of such a planet had not been disproved, although now it has been.

    I was wondering when exactly this was disproved, and at what point other hypothetical planets have been disproved. If there had been a terrestrial planet in Jupiter's stable 60 degree Lagrange point, at what point would it have been discovered?
    Last edited by Aetherium; 2018-May-07 at 04:51 PM.

  2. #2
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    Let me try the "terrestrial planet in Jupiter's L4 or L5 point" question. If Earth were placed there, it would be how bright? Well, Earth's radius is 1/13 of Jupiter's, so it has (1/13)*(1/13) = 1/169 of the surface area. Assuming that the cloudy Earth is roughly the same albedo as Jupiter (it's not, but the occasional specular reflections from the Earth's oceans would be brighter than clouds), that would make Earth 1/169 as bright as Jupiter appears to us. That's about 5.5 magnitudes fainter. Since Jupiter is around mag -2 to -3, we'd expect the Earth-like object to have an apparent magnitude of around +3. That should be visible to the naked eye from dark sites, so I would speculate that it would have been noticed by ancient astronomers such as the Babylonians, Chaldeans, Greeks, Chinese, Mayans, and so forth.

    If the object were the size of Mars instead of the size of Earth, it might hover on the border of detectability with the naked eye. In that case, you could guess that it would not have been noticed until after 1611, when telescopes were turned to the skies.

  3. #3
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    Would it be possible for a planet with an atmosphere to have a really low albedo? Presumably a low albedo would make any celestial body harder to detect.

    My idea was that the fictitious planet would have a really low albedo as well as an atmosphere with a lot of insulation from greenhouse gases.

  4. #4
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    Quote Originally Posted by Aetherium View Post
    Would it be possible for a planet with an atmosphere to have a really low albedo? Presumably a low albedo would make any celestial body harder to detect.

    My idea was that the fictitious planet would have a really low albedo as well as an atmosphere with a lot of insulation from greenhouse gases.
    Well, apparently water has a albedo of .10 which is very low - even lower than the Moon's 0.12 (the Moon's dust is charcoal grey).

    The biggest contributor to albedo is cloud cover. Not sure how you could get a habitable planet without having significant cloud cover.

    What if you went for some other quirk? What if the opposing planet's L1 point had collected enough dust to partially obscure it from us?

  5. #5
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    Would that make it harder for sunlight to reach it?

  6. #6
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    Quote Originally Posted by Aetherium View Post
    Would that make it harder for sunlight to reach it?
    You mean would the denizens of that planet experience dim sunlight? Sure.
    Would it mean Earthlings would have a tough time seeing it? Plausibly.

  7. #7
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    How about if it was an inner planet and had accumulated dust in its L2 point? Should that have the same effect in obscuring it from Earth?

    Incidentally, this guy reckons it's theoretically possible to pack 252 Earths into the habitable zone. Is that true?

    https://planetplanet.net/2017/05/03/...-solar-system/

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