Martian sky is BLUE, tell NASA!

[yevaud]

Going for post count of the day, Max?<br /><br /><img src="/images/icons/wink.gif" /> <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>

 

[maxtheknife]

Lol, Yevaud.... Yeah, ever since that <i>other</i> thread died down, my post count has dwindled! <img src="/images/icons/wink.gif" />

 

[yevaud]

Yeah, it was a pretty good thread. I wish more were like that. We managed to remain generally civil throughout, the debate was keen, and the data presented was quality. <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>

 

[silylene old]

thanks TheChemist and Jon.<br /><br />Taking the reference by Sneeps and Ubachs, and looking at the data in Table 2 and Part 6 (page 15) and combining, you can tally up the Raleigh scattering cross-section. I am assuming that cross-sectional data from the Part 6 discussion of O2 is comparable to the Table 2 data. (I think so)<br /><br />Scattering cross sections in units of 10^-27 cm^2<br />Ar 4.45<br />O2 4.50<br />N2 5.10<br />CO2 12.5<br />SF6 32.3<br /><br />Increasing scattering cross-section trend follows exactly as expected based on molecular polarizability, or London dispersion parameters, with SF6 being the most polarizable and thus the greatest amount of Rayleigh scattering.<br /><br />I think this data indicates that CO2 should be a more effective scatterer than O2. <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>

 

[telfrow]

And... <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[telfrow]

ignore <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[telfrow]

the <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[telfrow]

science (?)....<img src="/images/icons/wink.gif" /><br /><br />(I need to add a few to my post count too...) <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[maxtheknife]

No, not the science, just the scribbling <img src="/images/icons/wink.gif" />

 

[telfrow]

LMAO...nice one Max. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[thechemist]

<font color="yellow">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.</font><br /><br />Maybe what they mean to say is that since all common gas molecules are not much different in size (all much smaller than visible light wavelengths), the chemical composition is not important with respect to pure Rayleigh scattering. <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>

 

[yevaud]

Perhaps, though I am to the understanding that C02 (reflecting what's mentioned a few posts ago) is a much more efficient scatterer of the blue component than, say, 02.<br /><br />In any event, Mars still won't have much of a blue component, due to the low atmospheric pressure (I'm not certain about the figures for scale height and optical depth for Mars - have to think about it) and suspended dust.<br /><br />A great example is that picture taken of a Martian sunset. The transmission path is at it's maximum, so the scatter will be at it's lowest, true. You'll note that there's a bluish area around the setting sun, but elsewhere is gray/red/brown.<br /><br />No doubt the scatter at high noon would be greater (least optical depth), but even then it's not a pure blue sky by any means. <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>

 

[JonClarke]

ES wrote:<br /><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 />I think this is a very interesting observation that I have wondered about also. I imagine it might be be a bit like the effect of wearing those brown polaroid sunglasses. At first everything looks very brown buut you soon adjust and things look almost normal.<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>

 

[JonClarke]

But remember that the Martian sky is dominated by Mie scattering from (relatively) large particles, not gas molecules. The optical density is typically round 0.5 because of these.<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>

 

[yevaud]

That's so. There's likely a fair amount of Mie Scatter due to the suspended dust particles as well. <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>

 

[JonClarke]

Not likely - IS<br /><br />On a related matter, somebody asked at th rate of dust settling in the Martian atmosphere. This can be caculated from stokes law. <br /><br />For example, with a 100% CO2 atmosphere, using typical marian temperature and pressure profiles, the fall time for various sized particles from 10 km can be calculated, assuming no turbulence. All times terrestrial.<br /><br />10 microns: 7-8 days<br />5 microns: 16-20 days<br />1 micron: 91-116 days<br />0.5 micron: 185-236 days<br />0.1 micron: 2-3 years<br /><br />Since there are large dust storms every few weeks and dust devils several times a day, it is easy to see why there is so much suspended dust.<br /><br />Jon<br /><br />PS all data from Wells <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>

 

[yevaud]

Thanks. I have relatively little info. on that readily available, and not a lot of time today to research.<br /><br />Much obliged. <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>

 

[JonClarke]

You're welcome. It's all good fun and a great way to learn <img src="/images/icons/smile.gif" /><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>

 

[extrasense]

-- observation that I have wondered about also --<br /><br />Jon,<br /><br />If I where an astronaut on Mars, I would like rather to have the color rich vision that the Raw images give you, which could be provided by <b>Mars vision glasses</b>, than the dull yellow to start with, and then try to do the adaptation trick.<br />The same probably goes for a Martian creature <img src="/images/icons/smile.gif" /><br /><br />es<br /><br />