[X] My Assistant

[Guest_Sunspot_*]

Actually, people have already claimed to see jets/plumes of material erupting into the atmosphere from MOC images on this forum:

http://www.unmannedspaceflight.com/index.php?showtopic=1495

Those dark streaks look almost identical to the Nitrogen geysers discovered on Triton.

[Guest_gil nodges_*]

Interpreting these features as geysers/jets instead of wind eroded surface streaks sure makes this picture exciting! It appears that the geysers have already erupted and fizzled in the top of the picture (notice no streaks in this area). the center of the picture is peaking in activity creating a dusty haze and new eruptions are beginning in the lower portion of the picture. Can this really be true?

http://www.msss.com/mars_images/moc/2005/06/29/

[atomoid]

I'm with Bill. I think "roaring jets of CO2" may be an exaggeration, and somewhat misleading. Perhaps more in the nature of regular, gentle "burps". A mud pool instead of a geyser.

Steve

..but its so much more fun when you can have press releases with these kinds of images!

[mcaplinger]

Can this really be true?

Both of these images are illuminated from the upper left. All the "geyser interpretations" I've read only make sense if the images are illuminated from the lower right. Either the MSSS web release pages are wrong about the illumination direction, or the "geyser" interpretation is wrong. I checked with the author of the releases in question and he said he was pretty sure the illumination direction is as stated.

But, since both of these images appeared in the last Web release, you should feel free to check the illumination direction (the parameter may be confusing, but I know it's right because my software computed it ) and see if the Web releases are wrong.

[Guest_gil nodges_*]

So, why do the "wind streaks" suddenly disappear at the top of the image?

[djellison]

They don't suddenly disappear.

And if they did - why would that suggest that the people who built the camera and have operated it for nearly a decade have got the illumination angle wrong by 90 degrees?

If these were features of any height, we would see shadows extending down and to the right much as we do with dust devils...

http://www.msss.com/mars_images/moc/2006/07/17/
http://www.msss.com/mars_images/moc/2006/07/05/
http://www.msss.com/mars_images/moc/2006/06/08/
http://www.msss.com/mars_images/moc/2006/03/16/
http://www.msss.com/mars_images/moc/2006/01/20/

We don't see that. We do, however, see streaks that point not in the direction we would expect a shadow, but in the direction of the prevailing wind. The artists impression is a best, a huge dramatisation and at worst, complete fiction.


Doug

[Guest_gil nodges_*]

Hi Doug,

The streaks DO disappear at the top of the picture (whether they end suddenly, or not, is open for debate). In my mind, there are only 3 explanations for this. 1) the prevailing wind suddenly dies down, which is extremely unlikely in such a small sample of terrain 2) as more surface areas are exposed, it dilutes the visual prominence of the wind streaks, or 3) the streaks are composed of plumes of material that has been lofted into the air, and the top of the picture represents areas where the plumes have already dispersed and subsided.

http://www.msss.com/mars_images/moc/2005/0...29.S0602060.gif

I believe your point about shadows is very important, and certainly needs to be addressed, but doesn't necessarily mean this new finding is fiction. A few explanations I can think of that MAY explain the lack of shadows cast down and to the riht are:

1) plumes of dust/ice in the atmosphere creates a haze, which eliminates the shadows (like a cloudy day).

2) the illumination is not really from the upper left. I have no reason to doubt what I am being told, or the intentions/competence of the good people who are releasing the information. However, it is difficult to believe something that my own eyes tell me is not correct. For instance, the picture below says it is illuminated from the upper left, as well. Everything I see in this picture tells me otherwise.

http://www.msss.com/mars_images/moc/2005/0...30.S0800321.gif

Finally, in regards to the first picture, can someone explain the "hazy" center of the image? There appears to be a haze that is obscuring some of the streaks.

I'm not saying whether the plumes are real, or not, all I am saying is we must look at all possible explanations before writing it off.

[Guest_AlexBlackwell_*]

For instance, the picture below says it is illuminated from the upper left, as well. Everything I see in this picture tells me otherwise.

http://www.msss.com/mars_images/moc/2005/0...30.S0800321.gif

I guess my eyes are different than yours because the lighting to me looks precisely consistent with illumination from the upper left.

[djellison]

2) the illumination is not really from the upper left.

It is.Fact.

If your eyes tell you otherwise, then you need to alter your perception of the image. There's stuff that's open to interpretation, and there's stuff that isn't. The angle of illumination falls in the second catagory.

As for haze - this is a polar region, and the polar regions have a lot of clouds around, it wouldn't be unusual to have some thin high cloud over this sort of area.

Doug

[mcaplinger]

And if they did - why would that suggest that the people who built the camera and have operated it for nearly a decade have got the illumination angle wrong by 90 degrees?

Hey, we're not infallible. The "image of the day" release lighting direction could be wrong (I don't think it is, but it might be.) But the official PDS release on our Web site is pretty carefully computed and checked, so somebody should feel free to look at the images in question there and confirm that the lighting is as stated in the "image of the day" release.

I think it's a pretty safe bet that if there was anything remarkable in these images somebody at MSSS would have seen it, but I'm happy to keep an open mind about it.

[edited: I think the claim is that we got it wrong by 180 degrees, not 90 degrees ]

[djellison]

Well - to get it wrong by 180 you've got to go through 90 at some point

[Bill Harris]

Again, my take is that we have gentle puffs of fine dust which are blown by the prevailing wind to make streaks or by variable winds to make "clarke trees". Dust geysers makes good press, but strains the imagination otherwise.

--Bill

[mcaplinger]

Hey, we're not infallible. The "image of the day" release lighting direction could be wrong (I don't think it is, but it might be.) But the official PDS release on our Web site is pretty carefully computed ...

OK, I've checked the situation and it's a bit more confused than I wish it was. As has been discussed before, the definition for the cumindx.tab entry for SUN_AZIMUTH depends on a left-right "flip flag" in one of the other fields and is defined relative to the image that appears on the PDS archive volume. I had been under the impression that the "processed but not map-projected" version of the image in the MOC Gallery was identical to the PDS image, but it turns out that they are being rotated in some manner (at least for the more recent releases), but the SUN_AZIMUTH parameter is not being adjusted appropriately. I'm going to check to see if the people in charge of the gallery can clarify this situation. In the meantime the official PDS release is correct, which is the important thing.

That said, I checked image S08-00321 and the sun direction is as it says in the "image of the day" release, so I don't see how those dark streaks could be the shadows of geysers.

[dilo]

Looking to S0800321, it seems pretty evident to me that, indipendently from light direction, these dark features are streaks on the terrain and not shadows... in fact, they do not point exactly in the same direction and there are strong differences in the lenght/width, hard to explain as shadows; probably, that dark material pushed by sublimated CO2 is too rarefact to cast a shadow but, with prolongud eruption, is able to draw dark streaks in the prevalent wind direction over the ice sheet.
Interestingly, source of "gaysers" lies always in correspondance of bright features, presumably region of higher slope where more light penetrate and sublimate the CO2...

[john_carter_from...]

The shapes are formed by thin layers of dark dusty material that are sprayed by roaring jets of carbon dioxide that erupt through the ice cap.
Now THERE'S a place to place a lander with a 30 frame per second video capability! (if the camera doesn't get sprayed)
Don

The surface could be honeycombed and unable to bear loads in these places. Brings to mind the loss of Deep Space Two and Mars Polar Lander.