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Thread: Planets

  1. #1

    Planet Colors

    I like writing and I like science. While it can be a lot of fun to have fantasy worlds where the laws of physics are on vacation: Mars is actually a giant ruby! I also like to know more sound physics and chemistry answers: Mars isn't a giant ruby, it's covered in iron oxide. Please keep in mind that I'm new here and I haven't had time to look up all the answers to the questions below. If someone else has already asked them, please let me know and link me to that answer.

    Mars is red because of the iron oxide. Presumably if it had copper oxide instead it might look green. What other chemicals could yield other colors such as purple or yellow or anything else on a solid surface. I know water can make blue and sulfur can make yellow, but I'm looking for something 'dry' for blue and I'm less sure about a planet with an entire surface made of sulfur.

    In similar vein, I know methane causes the blues of Uranus and Neptune and sulfur causes yellows, but I again am not sure what other chemicals could be present in a gas giant/ice giant to produce red or purple or similar.

    Thanks in advance anyone that answers!

    *I have edited out my other questions and started posting them as separate threads, as was suggested by a couple people. I'm sorry for the confusion. Thanks to everyone that has answered so far!

    Separate from the chemicals:
    How might a "super-earth" have looked in the place of Venus or Mars?

    If we had a hot Jupiter or hot Neptune, what might it have looked like?

    If Venus had a moon relatively the same size as ours, when would it have been visible?

    If a Mars-sized world circled another, larger, world in the orbit of Mars, would both have been visible for ancient people? What about Venus?

    How long could two similarly sized planets rotate around a common barycenter?

    If Earth had a second moon, how far out would it have to be to be stable over a relatively long time (say around 8 billion years or so)?

    Would it have been possible for there to be three habitable Earth-sized worlds in our solar system, and if so where would they have to be placed?

    Is it possible to have an Earth-like world circle a gas giant? If so, at what distance from the main planet? What might fellow orbiters look like? Could it have it's own moon?
    Last edited by Indagare; 2011-Sep-05 at 12:19 PM. Reason: refining the question to one topic

  2. #2
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    Hi, Indagare!

    That's kind of a lot of different subjects for one thread.

    Regarding colors of planets, The red-orange color of Mars is the
    result of just a few percent iron oxide in the soil. Because the
    deserts of the southwestern US and northern Africa have very
    little vegetation covering the ground, you can easily see the
    red-orange color of their soil in photos made from space, also
    the result of a few percent of iron oxides.

    -- Jeff, in Minneapolis

    .
    Last edited by Jeff Root; 2011-Sep-05 at 02:40 AM.
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  3. #3
    "If Venus had a moon relatively the same size as ours, when would it have been visible?"

    I recall an essay by Isaac Asimov in which he noted that if Venus had a moon about the same size as Earth's, that moon would have been readily visible to observers without telescopes.

    He then noted that this would have led to the early acceptance of heliocentrism & greatly speeded the advance of science, by analogy with how the discovery of Jupiters moons removed a major objection to the theory. IIRC the essay title was 'The Tragedy of the Moon'.

    So assuming Asimov got his calculations correct such a moon would be visible any time Venus was above the horizon & there was full night rather than twilight.

  4. #4
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    Quote Originally Posted by Indagare View Post

    Is it possible to have an Earth-like world circle a gas giant? If so, at what distance from the main planet? What might fellow orbiters look like? Could it have it's own moon?
    I wondered about the existence of secondary moons (moons of moons) myself, especially about how the apparent motions of celestial bodies would look from there. But this is a thread on its own and so are all your other interesting questions.

  5. #5
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    You might look up photos and the associated science behind the colors on the moons of Saturn and Jupiter.

  6. #6
    Quote Originally Posted by Indagare View Post
    Mars is red because of the iron oxide. Presumably if it had copper oxide instead it might look green. What other chemicals could yield other colors such as purple or yellow or anything else on a solid surface. I know water can make blue and sulfur can make yellow, but I'm looking for something 'dry' for blue and I'm less sure about a planet with an entire surface made of sulfur.
    The last isn't that unlikely: http://en.wikipedia.org/wiki/File:PI...an_Changes.jpg

    Note that Mars isn't covered in iron oxide, it's just stained with a small amount of it, similar to Earth. It's a pretty effective pigment. Sulfur is much less effective, but heavy, constant volcanism has brought much of Io's sulfur to its surface. It's more than yellow, as well...different forms of sulfur are red and brown, and there's some volatile sulfur compounds that freeze out on the colder parts of the surface, making Io rather colorful.

    Various clays can be blue-gray. And actually, iron compounds are often blue and green...you might get them on a planet with a reducing atmosphere, one that still has a lot of free hydrogen (probably meaning a big planet, but a large terrestrial world might keep some).

  7. #7
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    Quote Originally Posted by Indagare View Post

    If we had a hot Jupiter or hot Neptune, what might it have looked like?
    If it has a deep atmosphere of hydrogen, helium and ices, the speculations of Sudarsky apply:
    http://en.wikipedia.org/wiki/Sudarsk...classification
    Quote Originally Posted by Indagare View Post
    If Venus had a moon relatively the same size as ours, when would it have been visible?
    Always.
    It would have been about 5 magnitudes dimmer than Venus, easily detectable by naked eye except when Venus is near a conjunction.
    Quote Originally Posted by Indagare View Post
    If a Mars-sized world circled another, larger, world in the orbit of Mars, would both have been visible for ancient people? What about Venus?
    Yes, easily.
    Quote Originally Posted by Indagare View Post
    How long could two similarly sized planets rotate around a common barycenter?
    What could hinder them?
    Quote Originally Posted by Indagare View Post
    If Earth had a second moon, how far out would it have to be to be stable over a relatively long time (say around 8 billion years or so)?
    That is harder... Pluto, Charon, Nix and Hydra works, but can someone compute the workable and unworkable options for Earth with multiple satellites?
    Quote Originally Posted by Indagare View Post
    Would it have been possible for there to be three habitable Earth-sized worlds in our solar system, and if so where would they have to be placed?
    Several options... but hard to tell which is best.
    Quote Originally Posted by Indagare View Post
    Is it possible to have an Earth-like world circle a gas giant?
    There are arguments from observed masses of gas giant satellites and supposed formation mechanisms, but given the surprises with observed exoplanets it is hard to tell what they are worth.
    Quote Originally Posted by Indagare View Post
    If so, at what distance from the main planet?
    Anywhere between Roche and hill limits
    Quote Originally Posted by Indagare View Post
    Could it have it's own moon?
    That could get hard, in view of tight Hill limits of the tertiary and tidal decay.

  8. #8
    Quote Originally Posted by Jeff Root View Post
    Hi, Indagare!

    That's kind of a lot of different subjects for one thread.

    Regarding colors of planets, The red-orange color of Mars is the
    result of just a few percent iron oxide in the soil. Because the
    deserts of the southwestern US and northern Africa have very
    little vegetation covering the ground, you can easily see the
    red-orange color of their soil in photos made from space, also
    the result of a few percent of iron oxides.

    -- Jeff, in Minneapolis

    .
    You're probably right that I should have had my other questions in different topics, but I didn't want to be annoying and make a dozen new threads all at once.. Of course, it may be annoying now to have all these here, so I might edit.

    Thanks for the help.

  9. #9
    Quote Originally Posted by chornedsnorkack View Post
    If it has a deep atmosphere of hydrogen, helium and ices, the speculations of Sudarsky apply:
    http://en.wikipedia.org/wiki/Sudarsk...classification

    Always.
    It would have been about 5 magnitudes dimmer than Venus, easily detectable by naked eye except when Venus is near a conjunction.

    Yes, easily.

    What could hinder them?

    That is harder... Pluto, Charon, Nix and Hydra works, but can someone compute the workable and unworkable options for Earth with multiple satellites?

    Several options... but hard to tell which is best.

    There are arguments from observed masses of gas giant satellites and supposed formation mechanisms, but given the surprises with observed exoplanets it is hard to tell what they are worth.

    Anywhere between Roche and hill limits

    That could get hard, in view of tight Hill limits of the tertiary and tidal decay.
    Thanks very much for all the answers! I'm putting the separate questions in different threads now, at least I hope, but this was all very helpful! I had no idea about Sudarsky.

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