IPB

Welcome Guest ( Log In | Register )

2 Pages V  < 1 2  
Reply to this topicStart new topic
Meridiani Ice theory, New theory for the formation of the Meridiani bedrock
Doc
post Feb 18 2009, 04:01 PM
Post #16


Member
***

Group: Members
Posts: 276
Joined: 11-December 07
From: Dar es Salaam, Tanzania
Member No.: 3978



Wow, thanks for abstract Niles. This is certainly going to be fit nicely in 'bed-time' readings.
Regards.


--------------------
We talk of nothing but Curiosity here
Follow me on twitter or Google +
Go to the top of the page
 
+Quote Post
centsworth_II
post Feb 18 2009, 04:17 PM
Post #17


Senior Member
****

Group: Members
Posts: 2173
Joined: 28-December 04
From: Florida, USA
Member No.: 132



QUOTE (ngunn @ Feb 18 2009, 08:28 AM) *
Thanks for that - it's a very interesting read. You mention 'a common formation process which must have acted over a large area of Mars'. Do you have a view on how much of Mars this ice sheet might have covered at its maximum extent?

This description from the LPSC abstract seems to indicate that the ice cap was perhaps even larger than today's polar caps, if my understanding is correct that the ice sheet being referred to was the actual polar cap back then.
"... massive dust/ice deposit that was located adjacent to Meridiani Planum. This massive dust/ice deposit... resembled the polar layer deposits that exist today in the martian north and south polar regions. Suspended dust... an important driver for the precipitation of water ice in the present day polar caps... would have been more prevalent on ancient Mars."
Go to the top of the page
 
+Quote Post
Paul Niles
post Feb 18 2009, 10:51 PM
Post #18


Newbie
*

Group: Members
Posts: 7
Joined: 17-February 09
Member No.: 4604



The idea -- as it pertains to the rest of Mars -- is a little vague right now. But, we imagine that other sulfates/layered deposits on Mars formed through a similar mechanism. We are not suggesting that ALL of Mars was covered by a single ice sheet, rather that at different times, during different epochs, ice accumulated in these areas (where we find layered deposits+sulfates) -- and this ice-weathering process took place.

It is striking that almost all sulfate deposits on Mars occur with similar characteristics -- they are in finely layered deposits, intimately mixed with silicates, the deposits drape topography, the layered deposits frequently overtop the rims of the chasm/crater in which they are located, the deposits frequently show evidence for having had a much larger extent and have been easily eroded.

If Meridiani truly formed through this ice-weathering process -- then I would think that it is very likely that other sulfate deposits on Mars formed in a similar fashion given the many similarities that have been noted by a number of other studies. However, this linkage requires a lot more work to strengthen.

Paul
Go to the top of the page
 
+Quote Post
ngunn
post Feb 18 2009, 11:34 PM
Post #19


Senior Member
****

Group: Members
Posts: 3516
Joined: 4-November 05
From: North Wales
Member No.: 542



Thanks Paul, that's very informative. I can see why the evidence to date doesn't pin down one scenario. But it seems to me that you are postulating either very mobile polar caps (a lot of polar wander) or a rather extensive ice sheet. Both are interesting. Can you post a map showing all the locations involved?
Go to the top of the page
 
+Quote Post
dvandorn
post Feb 19 2009, 03:36 AM
Post #20


Senior Member
****

Group: Members
Posts: 3419
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



I seem to recall asking, in the extensive and now closed discussions with Herr Doktor Professor about alternate theories on the development of the Meridiani deposits, whether what we're seeing might not be the result of Meridiani at one time being much nearer the pole, i.e., that there may have been glacial alteration in this region.

Nice to see that my vagrant thoughts occasionally pop up in other peoples' serious theories... smile.gif

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
Paul Niles
post Feb 19 2009, 05:09 AM
Post #21


Newbie
*

Group: Members
Posts: 7
Joined: 17-February 09
Member No.: 4604



I have no Map nor do I know if a map exists. Definitely something I'd like to see. I'm not sure if someone out there is keeping track of all of the sulfate deposits -- I have seen maps like that - check here. But I think these things are changing on the month to month basis as CRISM and OMEGA make new discoveries.

We currently have no comprehensive theory for ice deposits on Mars or how they got there -- we simply think they were at Meridiani. Now we pose two mechanisms for what may have happened:
1) Obliquity variations: Basically the angle of tilt of Mars' axis of rotation vis a vis the Sun is thought to have varied considerably with time. Sometimes dipping down to as low as 40 degrees from vertical. These obliquity variations could cause ice to be redistributed from the polar regions to the equator. The ice would then move back again when the obliquity became more vertical. This might provide a mechanism for depositing large amounts of ice early in Mars' history on the equator, and then removing it again.

2) Polar wander -- this idea is that the actual map location of the axis of rotation of Mars was in a different place early in the history of Mars (before the growth of Tharsis). As Tharsis grew, it caused the axis of rotation to migrate across the planet until it reached its final location. Everybody is pretty sure this happened, but no one knows how large of an effect it had. It could have only moved a few degrees, while it may have moved all the way from the equator. We speculate based on the antipodal hydrogen deposits, and layered terrain in Arabia, that a paleo-pole was located near Meridiani. But if you ask most Mars scientists who are familiar with this subject you would find extreme skepticism -- for valid reasons. Mostly having to do with age relationships of the terrain in question and the growth of Tharsis.
Go to the top of the page
 
+Quote Post
Shaka
post Feb 25 2009, 10:16 PM
Post #22


Senior Member
****

Group: Members
Posts: 1229
Joined: 24-December 05
From: The blue one in between the yellow and red ones.
Member No.: 618



Having at last gained access to and read your paper with Michalski, I can congratulate you on your contribution to the Meridiani provenance debate. I look forward to reading the responses of the MER P.I.s who presently sponsor the "warm, wet playa" alternative hypothesis. Probably some of those responses have already been aired at the LPSC, but those of us unfortunates unable to attend must languish in ignorance of the state of play. It would be tremendously exciting for UMSF members if that discussion could visit this forum, but those involved may prefer to rely on the traditional, slower, more thoughtful avenues of debate in the refereed literature. I'm not sure of my own preference in the long term, but I am eager to see the outcome of this collision of hypotheses.

You interpret the regionally-uniform, but locally-improbable chemical ratios of Meridiani sediments as the result of regionally-uniform, but locally-confined reactions in icy microcosms. I am wondering if your model permits quantification of the microcosm system to such an extent that you might be able to predict, at least approximately, the abundances of chemical species found at present. You emphasize, for example, the very limited abundance of water in your reactive system. Could this serve to predict the limited size of the "blueberry" concretions? This issue is one of considerable interest to many of us, including Don Burt, who has listed it among the reasons he favors his "brine splat" impact hypothesis over the greenhouse-playa model. I am less convinced that a series of random meteor impacts might produce the present picture of Meridiani sediments, but I would be strongly persuaded toward your "icy-test tubes" model if you could predict the size-distribution of blueberries. That's probably asking a lot, but, if beyond reason, might you suggest another quantitative observation that would permit a clear choice from the three models? (Or do you feel you have already done that?)

In any case let me add my thanks for your willingness to discuss your ideas in this forum. I hope your experience here will prove congenial enough to persuade other senior authors to emerge from 'lurk-mode' and join in our "cyber-seminar".




--------------------
My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
Go to the top of the page
 
+Quote Post
Paul Niles
post Mar 2 2009, 04:36 PM
Post #23


Newbie
*

Group: Members
Posts: 7
Joined: 17-February 09
Member No.: 4604



I love the "icy test tubes model" -- can I use that in the future?

The blueberries are certainly the most perplexing and interesting feature of the meridiani sediments and I'm afraid my paper makes no significant inroads towards discovering how they formed. I think the best work done to date is that by D.C. Golden also here at JSC. He has done some experimental work that shows that one can form Hematite spherules with identical characteristics to the blueberries through forced hydrolysis of Fe by supersaturated solutions. Check out a recent LPSC abstract if you don't have access to the article.

Now, D.C.'s work needs temperatures >100 C to form the hematite - and I don't know how you get those conditions over such a wide area of Meridiani (tens of thousands of square kilometers). Another thing about DC's work is that his blueberries are about an order of magnitude smaller than the Meridiani blueberries. He suggests that lower temperatures and longer time periods should act to make larger blueberries. So size distribution may just be a function of the time, temperature, and chemical compostion of the fluids.

Also, a key observation is that the hematite spherules are evenly distributed within the outcrop making it almost certain that they grew during diagenesis after deposition. I know that Dr. Burt disagrees with me on this, but I think the MER team has done a thorough job making this point. So the blueberries didn't form inside the icy test tubes, but rather formed after the sediment had been reworked by eolian processes (maybe some impacts played a role as well).

Our model predicts that the chemical composition of the outcrops should be very similar to the chemical composition of the dust in the atmosphere (with only very minor loss of the most volatile elements). The icy-test tubes are closed systems so there should be no addition or subtraction of elements from what was incorporated in the ice.
Go to the top of the page
 
+Quote Post
Shaka
post Mar 2 2009, 10:47 PM
Post #24


Senior Member
****

Group: Members
Posts: 1229
Joined: 24-December 05
From: The blue one in between the yellow and red ones.
Member No.: 618



Please accept "icy test-tubes" with my blessing. (I suppose that will put me in the cheering section for that hypothesis. wink.gif )
Thanks for the DC Golden reference. I should be able to access it in the library later this week. It sounds like a promising line of research if the temperature and concretion size can be varied experimentally. I suppose the three models fall out on the temperature scale with the impact model on the hot end, the icy test-tubes on the cold end, and the greenhouse-playa somewhere in between? I understood that you assumed concretion formation to occur in the "post test-tube" phase of diagenesis.

I meant to ask how "festoon cross-bedding" accords with your hypothesis. Does your low water-mineral ratio scenario provide enough fluid to produce the occasional festoon? I have to say that for a feature so vigorously celebrated by the MER P.I.s, clear examples of festoons have proven to be 'rare birds'. I was hoping the walls of Victoria Crater would provide a few examples. Perhaps the long march to Endeavour will turn some up.

So then, whose court is the ball in now? (This three-way tennis is a complicated game!) Is someone going to bat for warm, wet playas? (Sports metaphors can get complicated too!) cool.gif
The cheering section is all ears.


--------------------
My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
Go to the top of the page
 
+Quote Post
imipak
post Mar 3 2009, 08:57 PM
Post #25


Member
***

Group: Members
Posts: 646
Joined: 23-December 05
From: Forest of Dean
Member No.: 617



QUOTE (Shaka @ Mar 2 2009, 10:47 PM) *
I have to say that for a feature so vigorously celebrated by the MER P.I.s, clear examples of festoons have proven to be 'rare birds'. I was hoping the walls of Victoria Crater would provide a few examples.

I may be mis-remembering, but I thought unofficial identifications had been made? See, e.g,. http://www.unmannedspaceflight.com/index.p...ost&p=82403 ;
http://www.unmannedspaceflight.com/index.p...st&p=106462

I could have sworn festooned cross-bed forms had been spotted in the ramp surface at Duck Bay, and in Cape St Mary / Cape Verde? unsure.gif


--------------------
--
Viva software libre!
Go to the top of the page
 
+Quote Post
Shaka
post Mar 3 2009, 10:27 PM
Post #26


Senior Member
****

Group: Members
Posts: 1229
Joined: 24-December 05
From: The blue one in between the yellow and red ones.
Member No.: 618



I've been looking hard for festoons for years now and I don't remember seeing any convincing examples in close-up (i.e. with diagnostic features such as T-junctions) anywhere in Victoria. I'm sure the MER team would have pointed them out, had they recognized any. Of course, at a distance, such as in the many panoramas of the capes, there are numerous areas with variously 'wavy' laminations that resemble festoons in scale. These would be worth examining up-close for diagnostic features, but I can't remember any that were. I'll stand by my assertion, pending photographs that point out the alleged festoons.


--------------------
My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
Go to the top of the page
 
+Quote Post
Paul Niles
post Mar 4 2009, 12:39 AM
Post #27


Newbie
*

Group: Members
Posts: 7
Joined: 17-February 09
Member No.: 4604



I've never been too convinced by the "festoon" cross bedding. If you go back and watch the press conference they had on this, the independent expert that was brought in (I believe he was from USGS) showed some duneforms that looked alot like dunes on Mars. I think Paul Knauth has also shown some pretty convincing "festoon" cross bedding that was caused by base-surge deposits. If I had the time I'd go back and post that press conference. Anyhow, the icy test tubes theory is in luck because we've got a kilometers of ice just next door. So if we want some liquid water flow, we can invoke a little melting and boom we've got a valley network and some festoon cross bedding to go along with it.

Although you have to keep in mind that as a geochemist I feel that the chemical evidence is much more compelling than the geomorphic evidence.

Paul
Go to the top of the page
 
+Quote Post
dburt
post Mar 4 2009, 01:09 AM
Post #28


Member
***

Group: Members
Posts: 384
Joined: 4-January 07
Member No.: 1555



QUOTE
... I could have sworn festooned cross-bed forms had been spotted in the ramp surface at Duck Bay, and in Cape St Mary / Cape Verde? unsure.gif

Yes, and apparent festoon-like features are also exposed towards the lower right of Cape Victory, imaged just before Victoria Crater was left behind last October:
http://qt.exploratorium.edu/mars/opportuni...G3P2365R2M1.JPG
As Shaka notes, it is perhaps safest not to make too much of these cape exposures, inasmuch as they were not officially commented upon, and could not be examined up close. Of course, it might have been safest for all concerned if apparent festoon-like features seen in exposures elsewhere had not been commented upon either, because the claims initially made for them seem inconsistent with later data and interpretations.

Paul N. - There's no evidence of any "valley network" associated with any festoon-like feature seen yet, or for any channels or other obvious liquid water-related features at all, which is one reason why Paul Knauth and I are, like you, unconvinced. The ephemeral valley networks seen elsewhere on Mars seem to be associated with considerably older surfaces than the top surface of Meridiani.

-- HDP Don
Go to the top of the page
 
+Quote Post

2 Pages V  < 1 2
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 29th March 2024 - 03:08 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member.