Martian sky is BLUE, tell NASA!

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JonClarke

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I suspect it might convince some, but others, perhaps most, won't be. But I might be pleasantly suprised.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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JonClarke

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Thanks for this, it is a really fantastic site, especially as they use all visible bands, not just three. But will it convince everyone? I suspect not, as the whole business has been subsumed into grand NASA conspiracy theories<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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thechemist

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It was slinted, I posted the same link the "Images of Mars" thread a while ago <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>
 
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silylene old

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Pancam is an excellent site! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>
 
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JonClarke

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Meaning?<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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centsworth_II

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Well, that clears that up... not!<br /><br />Stevehw33 said: <br />"Until the next wild assertion is spewed out. then you will change your position..."<br /><br />Better make yourself clear. WHO will change their position in response to the next wild assertion? <div class="Discussion_UserSignature"> </div>
 
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JonClarke

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Exactly!<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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JonClarke

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I've just managed to get a copy of R. A. Well's 1979 book "Geophysics of Mars". Despite its date most of it is pre-Viking. Wells makes the point very clearly that C)2 does not scatter visible light to a noticeable degree. A dust-free, pure CO2 atmosphere will have a black sky. It is also clear tha ground measurements showed the Martian atmsophere contains 5 times the amount of dust that were predicted from terrestrial observations. With this caveat Well's prediction of the Martian sky with strong Mie scattering from suspended dust is remarkably accurate.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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yevaud

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Mmm. I recollect being informed in school that there *may* be a slight bluish tinge due to Mie scattering (this would be more or less at the zenith, where the optical transmission path goes through the densest aspect of the Martian atmosphere with respect to the observer)), but that in general, the Martian sky will be reddish (suspended dust) or blackish (no scatter). <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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silylene old

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Jon, I realize you read in R. A. Well's 1979 book "Geophysics of Mars" that CO2 does not scatter light appreciably.<br /><br />However, as a chemist, I am quite skeptical of this claim. I would like to see some valid data before I accept his assertion as fact.<br /><br />Why? In the scattering function, scattering increases as a function of alpha^2, where alpha is the molecular polarizability. Polarizability is the ease at which a molecule's (or atom's) electron density can be distorted. CO2 has a London dispersivity parameter (i.e. ability to polarize) about 1.5x that of N2, and it is typical of other "polarizable molecules". In fact, the reason that supercritical CO2 has solvency power is that the molecule is polarizable (which is what got me thinking that it should be a scatterer!).<br /><br />Point is, on the basis is that CO2 is polarizable and has a significant London dispersitivy parameter, I would also expect CO2 would be an effective Raleigh scatterer. I couldn't find any reference to this googling. Maybe I should check SciFinder when I get to work. So if CO2 truly isn't an effective scatterer, then I would like to know why, for this would be interesting in and of itself since it would contradict expectation. But I would need to be first convinced that this data itself is valid and accurate.<br /><br />Then, I am not an expert on this particular field of chemistry. But then again, I am known to do pretty well in the "intuitive" chemistry area. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>
 
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JonClarke

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Silyene<br /><br />Well, I am outside my comfort zone on this one. The exact quote (p316) is :<br /><br />"..the brightness at zero phase of a 6.25 mb CO2 atmsophere integrated over the disk varies from about 0.004 at 4500 A to about 0.001 at 6100 A of a pure white Lambert reflector under the same illumination conditions. Since the Rayleigh scattering pattern is the same in both the forward and rear hemispheres, these numbers are also approximately valid at the surface of the planet for the brightness of the sky in the direction of the overhead sun - only the expontential extinction term would be slightly smaller because of the single optical traverse. Hence, a pure CO2 atmosphere on Mars would yield a black Martian sky."<br /><br />I have done a bit of further searching on the internet and vatrious databases, and have not been able to find anything of the effect of different gases on Rayleigh scattering. So this is about as far as i can go.<br /><br />One (possibly inane) question though. Does polarisation automatically imply scattering?<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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JonClarke

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Indeed it does, that is why the Martian sunsets are blue.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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JonClarke

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This might be of interest. Here is some spectral radiance data from page 4405 of the the Viking spectrophotometric paper I referred earlier (Huck et al, J Geophys Res 62:4401-4411, 1977).<br /><br />They show that at both Vking landing site and in both cameras the martian sky and surface have essentially the same spectral radiance, except the sky ia brighter. The orange- red part of the sky spectrum (0.6-0.7 microns) is approximately twice as bright as the blue-violet (0.4-0.5 microns) part.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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JonClarke

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Here it is! <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>
 
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extrasense

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Jon,<br /><br />while you are basking in the warm glow of victory,<br />consider that constant Red highter relative intensity, can be mitigated by eye adaptation, so that on the average sky would be perceived as white.<br /><br />e <img src="/images/icons/smile.gif" /> s<br />
 
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silylene old

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Jon,<br /><br />It's outside of my comfort zone too. I know that fellow's data does suggest that CO2 will not scatter much....but it just doesn't make sense that this would be the case. Someone muct have looked into "why". I will do a little digging and post if I find anything. <br /><br />Maybe it is just that the CO2 was at such a low concentration in his study (6.25 mB). <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>
 
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thechemist

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A recent reference :<br />Direct measurement of the Rayleigh scattering cross section in various gases<br />Maarten Sneep,Wim Ubachs<br />Journal of Quantitative Spectroscopy & Radiative Transfer 92 (2005) 293 –310.<br /><br />And a rather old one : <img src="/images/icons/smile.gif" /><br />SCATTERING OF LIGHT BY CARBON DIOXIDE, NITROUS OXIDE AND SOME ORGANIC VAPOURS.<br />A L Narayan 1923 Proc. Phys. Soc. London 36 32-36. <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>
 
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thechemist

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According to Mars Now Team and the California Space Institute :<br /><br /><i>"If the Martian atmosphere were to be completely cleansed of dust, the daytime sky would appear blue, just as our own sky, because of Rayleigh scattering by the molecules (primarily carbon dioxide molecules) which make up the atmosphere."</i><br /><br />According to this site: <br /><br />"What color is the sky on Mars?<br /><br />At night, of course, it's black. During the daytime, scientists once expected to find a blue sky because of Rayleigh scattering (the process that colors the sky blue on Earth - the shorter wavelengths of light are more easily scattered, so it is mostly the blue light from the Sun that we see elsewhere in the sky.) However, when first the Vikings and then the Pathfinder landed on Mars, they saw a pink sky. This color comes from the ubiquitous Martian red dust which is stirred up by the winds and carried up into the atmosphere so much that the sky takes on the color of the dust."<br /><br />Also, this non-scientific site states:<br /><br />"Notice that this argument [the Rayleigh blue sky] depends very little on the composition of the atmosphere. Any clear atmosphere of more or less Earthlike size and density, lit by a sun whose light appears more or less white, would result in a blue sky." <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>
 
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yevaud

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Hmm. That non-scientific site is, of course, dead wrong. Rayleigh scattering is wavelength-dependent, which is to say that an atmosphere's constituent specie's are half the equation - size of the molecule vs wavelength. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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maxtheknife

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Sheesh! <img src="/images/icons/rolleyes.gif" /> <img src="/images/icons/smile.gif" />
 
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