Printable Version of Topic

Posted by: fallofrain Aug 26 2005, 01:51 AM

While browsing images from the MOC, I came across this photograph. I contacted the Planetary Science Institute and the editor of an astronomy magazine about it. Their belief was that it is probably dust blowing from a crater. We all agreed that it is probably not a dust devil. I have no reason to doubt their conclusion. It is probably correct. But the romantic in me wants it to be something a little more unusual. An ice geyser, perhaps, or venting gas.

I've had at least a cursory look at almost all MOC images. I've never seen anything like this. Dust devils tend to move in nearly vertical columns. This appears to be blowing downwind from a stable point source. There is no evidence I can see of other dust features (dunes or devil tracks) in the frame. The width of this photo is 2.97 km. It's cropped from MOC image R1801150. Other than cropping, it hasn't been enhanced in any way.

I wanted to post this to see if anyone would like to make comments. So how about it? Any ideas?

Posted by: dvandorn Aug 26 2005, 04:02 AM

Hmmm... I don't think I necessarily agree with the assessment that the image shows anything actively being blown out of the crater. If you'll notice, the two most obvious "lobes" are arrayed exactly radial to their origin point. If these were lobes of a geyser or even a windblown plume, I would expect them to begin to travel the same direction (downwind) when they got a short distance away from whatever physical feature was separating them. There is no sign that either feature is arrayed anything except radial to the origin point.

Also, while the two "plumes" located at about 3:30 and 4:30 (in clock-face angles) are the most visible, there are degraded remnants of very similar features at about 10, 11:30, 12:30 and 1:00 angles -- all exactly radial to the same origin point as the two prominent features at 3:30 and 4:30.

These may all have been created by windblown sediments, but it would appear to me that each of them would *have* to have been created during a time when the wind was blowing from a different direction than when any of the others were created. So, I've got to say, it's pretty obvious that these are all static features lying on the ground, that may well have been caused by dust plumes emanating from the crater, but I don't think any of them are actual dust plumes or geysers hanging in the air at the time the image was acquired.

-the other Doug

Posted by: Richard Trigaux Aug 26 2005, 11:01 AM

As far as we can see, it seems obvious than these features are static ground features, and not actually moving plumes. How they formed is however a bit difficult to guess. The best explanation I see is that it is a low velocity impact crater. Such craters are often irregular or containing blocks, like this one. And what we see is perhaps the main ejecta plume which fell on the ground on an oblique angle, likely from a very low angle impact. But we cannot say more accurately without further enlargement of this feature.

It is to be said that the scientist analysing MOC images and other planatary images do not pay much attention to the many strange looking images like this one. For the geologist eye these features do not look strange at all, just funny.

Posted by: Bob Shaw Aug 26 2005, 11:04 AM

It's certainly an odd image. The 'clock-hands' are unusual, though I don't see them as being anything other than a surface feature.

Posted by: fallofrain Aug 26 2005, 02:11 PM

Thanks for your input everyone. I had seen the feature extending from the crater at the 3:30 position as the plume. Considering the sun angle, I interpreted the darker streak at about 5 o'clock as a shadow from the "plume".

Thanks for your help.

Posted by: helvick Aug 26 2005, 03:10 PM

Looking at the full image for context http://www.msss.com/moc_gallery/r16_r21/full_jpg_non_map/R18/R1801150.jpg

You can see there is another similar crater SSW of this that also has similar but slightly less distinct lobate "plumes" that are at different angles (10, 11, 1, 4, 6 on the clock).

With this resolution and no further data there's little you can do beyond guess but looking at it in context the shading looks like eroded ejecta not a shadow from an opaque object. The intensity of the light on the NW side of the presumed shadow doesn't fit while it does fit with the conjecture that it is an eroded bank of ejected material from an impact, a feature it shares with the rays from the other crater.

Posted by: Richard Trigaux Aug 26 2005, 04:45 PM

There is perhaps something in the terrain which makes stronger rays. What is strange is that these two rays start from the center of the crater, not from the rim. There are even some craters inverted by the erosion (the botton of the crater is higher than the surrounding ground).

Posted by: helvick Aug 26 2005, 05:13 PM

Crater beds producing inverted crater mesa's after eons of erosion is seen in a lot of images and isn't hard to understand given the 100MY->GY ages that are likely for much of the surface. The point about the "plume" source point is very valid though and casts some doubt on my assessment. I still think it's a set of ridges but a better explanation of how they came about is needed.

Posted by: Astrophil Aug 26 2005, 05:17 PM

>I've had at least a cursory look at almost all MOC images

Crumbs!

I'm sure you know about the MOC public target request programme - might this be a candidate for it? They say they don't normally do reimaging unless there's a good reason, but in this case reimaging would certainly establish if this is a dynamic rather than a static feature.

Posted by: ElkGroveDan Aug 26 2005, 05:43 PM

In these days of Photoshop and hoaxes everywhere, it's probably a good idea to also reference the original MGS link.

I'm not suggesting that you have created a hoax, but it's just good practice. It saves everyone a lot of time, especailly those of us who would like to locate the original without doing an extensive search.

Posted by: fallofrain Aug 26 2005, 06:45 PM

I appreciate your concern about hoaxes. That's why I included the reference to MOC photo R1801150. The area is to the SE of the Hellas Basin. You are absolutely right about referencing the link. I'll see if I can cut and paste it from the MSSS site.

Posted by: fallofrain Aug 26 2005, 06:50 PM

Posted by: fallofrain Aug 26 2005, 06:52 PM

http://www.msss.com/moc_gallery/r16_r21/images/R18/R1801150.html

Here's the link to the photo. Sorry. I should've done this to start with.

Posted by: Bob Shaw Aug 26 2005, 11:21 PM

I suppose that a glassy ray structure might tie together some crumbly material, and resist erosion, so that when it was exhumed a ridge might form (a bit like the Empty Quarter craters on Earth)...

Posted by: garybeau Aug 27 2005, 12:20 AM

There appears to be a central peak or very large rock in the middle of the crater. Might that be acting as a wind break and allowing dust to settle behind it similar to what we are seeing on top of husband hill but on a much larger scale. As the prevailing wind changes direction, a new dune is created on the leeward side of the peak.

Posted by: fallofrain Aug 27 2005, 03:13 AM

Posted by: fallofrain Aug 27 2005, 03:21 AM

Please excuse my awkwardness in replying. I'm still trying to learn how to navigate through the posting menus and am having some difficulty. The "Help" feature -- doesn't.

To answer Astrophil's question... I know about the Public Target Request. I tried making a request for another feature when they first began the program. They seem to be pretty adamant about their "no repeat images" policy. Depending upon the comments I receive here I might try again with this image. Thanks for the suggestion.

Posted by: Palomar Aug 27 2005, 01:23 PM

*Looks like impact ejecta patterning. It seems the upper right-hand portion of the crater is deeper, as if an impact had struck hardest there. The splay pattern seems to suggest this as well.

Just a thought.

Posted by: fallofrain Aug 30 2005, 04:34 PM

For everyone's information...I've submitted a public request to Malin to have the site re-imaged. I'm not especially optimistic about that happening, though. I'd like to thank all of you for your ideas. If Malin does photograph the area again, I'll post the image here. Meanwhlie, I guess.....we wait.

Posted by: fallofrain May 25 2006, 02:55 AM

I've noticed that there is still some interest in this and in my more recent posting. If anybody has any additional comments, I'd love to hear them.

Terry