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Thread: Gas giant colors

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    Gas giant colors

    I've been given to understand that the reason Jupiter is banded brown and Neptune is blue, is because of the arrangements of hydrocarbon compounds in their respective atmospheres. I've also been told that these compounds are sensitive to sunlight and temperature which can alter their composition.

    Now if the two types of planet were to switch places in the Solar System, how would that affect the visible coloration of each one in the long run? Would we get a blue Jupiter and a rusty Neptune?
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    Quote Originally Posted by Noclevername View Post
    I've been given to understand that the reason Jupiter is banded brown and Neptune is blue, is because of the arrangements of hydrocarbon compounds in their respective atmospheres.
    A few years ago I saw the use of the term "chromophore" used to tell us that it is unknown just what it is that makes Neptune such a saturated blue. Have they figured it out?

    I've also been told that these compounds are sensitive to sunlight and temperature which can alter their composition.
    Rayleigh scattering can be a kind of sensitivity to sunlight. Take a look at this image of a blue Saturn.. Here is a better picture of the surprising Saturn blue sky since it shows that it is regional (northern hemisphere). I am fairly sure this occurs when the atmosphere becomes clear and Rayleigh scattering wins out over Mie (or other) scattering. It may be kind of a rare event.
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    Quote Originally Posted by George View Post
    A few years ago I saw the use of the term "chromophore" used to tell us that it is unknown just what it is that makes Neptune such a saturated blue. Have they figured it out?
    The usual explanation is that methane results in blue, with a contribution from unknown organics.
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    Pure Rayleigh scattering would, for obvious reasons, produce a planet of pure white, except at limbs being blue.
    Care for an explanation?

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    Quote Originally Posted by chornedsnorkack View Post
    Pure Rayleigh scattering would, for obvious reasons, produce a planet of pure white, except at limbs being blue.
    Care for an explanation?
    Sure. Under what circumstances would pure Rayleigh scattering occur?
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    Quote Originally Posted by Noclevername View Post
    Sure. Under what circumstances would pure Rayleigh scattering occur?
    For Rayleigh scattering, existence of polarizability and random inhomogeneity of atom distribution suffice.
    Absorption requires available excited states of suitable energy.

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    Quote Originally Posted by chornedsnorkack View Post
    For Rayleigh scattering, existence of polarizability and random inhomogeneity of atom distribution suffice.
    Absorption requires available excited states of suitable energy.
    What real-world(s) conditions determines whether the scattering is partial or pure?
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    Quote Originally Posted by Noclevername View Post
    What real-world(s) conditions determines whether the scattering is partial or pure?
    Presence of states capable of causing some absorption.

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    Quote Originally Posted by chornedsnorkack View Post
    Presence of states capable of causing some absorption.
    What physical condition causes those states? I mean what chemicals or light levels/spectrum?
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    Well, for example water is blue because of a series of overtones of O-H stretching vibration, whose mainline is at 2900 nm - and the overtones go to visible.
    Does methane also have blue colour due to overtones?

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    Quote Originally Posted by chornedsnorkack View Post
    Does methane also have blue colour due to overtones?
    I don't know. That's the kind of information I was hoping to find out by starting this thread.
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    Quote Originally Posted by chornedsnorkack View Post
    Well, for example water is blue because of a series of overtones of O-H stretching vibration, whose mainline is at 2900 nm - and the overtones go to visible.
    Hang on, that statement could easily be interpreted as the explanation that oceans on Earth look blue. But that's because of Rayleigh scattering in air, all water is doing is reflecting it. If oceans were mirrors, the Earth would look more or less the same. Think of moonlight reflected off the ocean. (Methane is different, it really does tend to look blue.)
    Last edited by Ken G; 2016-Mar-25 at 12:54 PM.

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    Quote Originally Posted by Ken G View Post
    Hang on, that statement could easily be interpreted as the explanation that oceans on Earth look blue. But that's because of Rayleigh scattering in air, all water is doing is reflecting it. If oceans were mirrors, the Earth would look more or less the same.
    No.
    Water is blue in both transmitted and scattered light, because it has inherent absorption of red light. Even a few metres of water in swimming pools are detectably blue.

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