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Earthlike Mars?
ngunn
post Feb 8 2012, 02:28 PM
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A relevant LPSC abstract on the stability of subsurface ice:
http://www.lpi.usra.edu/meetings/lpsc2012/pdf/2260.pdf
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ngunn
post Feb 8 2012, 11:29 PM
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I'll add a couple of comments about the abstract just posted. First, it shows that ice at 1m depth is stable down to latitude 40. That makes the story about the dielectric constant in the recent ESA press release (reported so clearly by Emily) a bit less tidy, I think. Second, they provide a graph on which there is really only one point of interest: for a single depth the critical latitude is 40 degrees. This leaves me with questions. How does the critical depth for ice survival vary with latitude? What is it at the equator?
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TheAnt
post Mar 31 2012, 04:30 PM
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Once upon a time we thought that there had been lakes in Valles Marineris. It was actually not that long ago, but around the time of the Viking lander/orbiter mission.

Then more lately when "our" rover Opportunity started to drive around in Meridiani Planum. It was at first thought to be a lake bottom or even might have been part of one inland ocean.

This idea had the problem with the local geography that could not really contain a lake, but also that nobody could find any shoreline for it. Add to that the finding that the water must have been quite sulfurous it would not have been any ordinary lake at all. Our planetary scientists then proposed a sort of marshland surrounded by desert as mr Squires have talked about in his updates about the mission.

A solution to this problem might be found in the text below which describe research that show how glaciers could have collected sulfur and ash from volcanic eruptions and so would have become quite acidic and resulted in the landforms, sediment layers etc, that we previously have thought formed by running water.

I have not been ready to embrace the cold Mars theory for a number of reasons, among them some sedimentary deposits and what appear to be river beds.

Now glaciers do the same work in creating valleys with flowing curving paths that look what we humans think of a riverbeds.
Many river valleys in my area were in fact first made by glaciers, it is only later that water have taken the same path.
One lingering mystery on Mars have been that we found no clays at first, we've found some now in later years, yet rivers that would have flown for a longer would have produced clays, but glaciers can indeed have this impact on landforms without producing much so also this fit with the observations.

Now that it turn out that these non-volcanic sediments are glacial in nature. And that water located under the icesheets that might have hydrated the minerals. I have finally started to cave in to the idea.
So to me this appear the cold and dry Mars scenario get increasingly more plausible. And we might very well have had one earthlike Mars, but only very early in the history for the planet.
(And this the reason I posted this, and with any apology if there's another thread started on this matter elsewhere.)


Mars Daily website
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Explorer1
post Apr 1 2012, 06:21 AM
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Aren't glacial valleys U-shaped while liquid rivers form V-shaped valleys? Basic physics are universal as far as I've heard.
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Phil Stooke
post Apr 1 2012, 11:59 AM
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That may be true but it doesn't tell us much here, with 3 billion years of talus formation obscuring the original shape.

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TheAnt
post Apr 2 2012, 10:34 AM
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Yes that is very true. And river like features might have been created in shorter time spans than what one might think.

Since the late Pliocene glacial period here on Earth glaciers and rivers have alternated in shaping the valleys of the arctic and sub arctic regions, in some cases creating new flows and breaking trough ridges as late as in the last 10.000 years.
So those valleys have been created in a very short time, and have either shape without conclusively telling which way it got started originally. And this might be a good analog for Mars, where some valleys have been carved by both water and ice.

@Explorer1: This finding by the Planetary science institute researchers do not rule out all formations as possible ancient lakes or river beds. There's no doubt there have been liquid water in some places like Nanedi Vallis, that have relatively few craters and so appear to have had a flow in a more resent age.
The question is of that valley were filled with water in one of the 'flash floods' described in some models, or that water did flow for a longer time under one ice sheet or even beneath a glacier. Stating "Sustained Water Flow?" with a question mark there.

The main point of that Mars daily item is that the layered deposits that have been found in many other areas might have been created by glaciers and not by pools or lakes of liquid water as previously thought.
Since the studies by the MER rover is of great interest for many on this forum I found it interesting that the text mentioned that such glaciers might be the explanation for the deposits found by Opportunity at Meridiani. I still wonder if that is consistent with the hints of karst topography that's been seen there though.
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TheAnt
post Aug 18 2012, 01:22 PM
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Well it seem that Mars have more signs of plate tectonic activity

The item describe this as entirely new, yet I am certain that many of us Marsophile people here on this forum are aware that the shield volcanoes of Tharsis montes looked quite similar to certain features on Earth where a continental plate have moved over a hot spot of the mantle. (Those from USA might compare to volcanos of Hawaii)
Whereas Valles marineris already have been suspected of being a feature similar to Rift valley in Africa.

http://www.sciencedaily.com/releases/2012/...55831.htm">Science daily on Plate Tectonics On Mars</a>

Edit to get a working link.
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elakdawalla
post Aug 18 2012, 02:53 PM
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If the press release is anything to go by, the paper is just plain bad. However I have enough experience with press releases to know that the release may not accurately represent what's in the paper. In either case, there is no evidence for Earth-like plate tectonics on Mars. The faulting in Valles Marineris is pretty convincingly a result of loading etc. from the Tharsis complex.


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Phil Stooke
post Aug 18 2012, 03:33 PM
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There has also been an attempt to explain the northern 'ocean' basin as a product of plate spreading. I'm not at all convinced. If you want to demonstrate plate tectonics you would need a global pattern of tectonics, not a local one resembling a product of horizontal motion. The image I've seen, in Melas Chasma, doesn't look like strong evidence to me, but I will admit I have not yet seen the full paper.

Phil


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TheAnt
post Aug 18 2012, 04:04 PM
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Thank you both.

Yes I did feel a bit hesitant on this item also, why I used 'signs of' (perhaps should have added 'that could have been interpreted as' in addition to the the 'look similar' and 'suspected'.

And I did indeed think the headline "Scientist Discovers Plate Tectonics On Mars" were a bit jumping to a one unproven conclusion. Yet I did find this item interesting enough for a heads up. =)
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Ron Hobbs
post Aug 18 2012, 05:17 PM
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The author of the Science Daily article seems to unaware of the Mars Global Surveyor findings a decade ago. A search turned up the 1999 press release right away.

Plate Tectonics on Mars?

I wonder if Yin referenced that discovery in his paper. Anyway, he was certainly not the first to discover evidence of incipient Martian tectonics. At least the NASA release was a bit more tentative with the inclusion of the question mark.

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dvandorn
post Aug 19 2012, 03:12 AM
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There are several Martian "features" which do resemble the results of plate tectonics on Earth, like the moving hot spot that seems to have left volcanoes all in a row in Tharsis, and the magnetically striped surface in the southern heavily cratered terrain.

However, as Phil very rightly points out, there are no features extant on Mars that suggest plate subduction. I can imagine a number of different possible models, including an early period when Mars' crust was rotationally uncoupled from the mantle, which could account for the tectonic-like features we do see. After all, there seems to be good evidence that the Moon's solid crust and nearly solid mantle are even now rotationally uncoupled from its small, purportedly molten core. Perhaps impacts large enough to leave enormous basins, like Imbrium or Hellas, have the ability to uncouple the crust from the mantle for shorter or longer periods of time.

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Phil Stooke
post Aug 19 2012, 09:42 PM
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On Earth hotspots stay fairly static and the crust moves over them. If Tharsis Montes are formed that way why is Olympus Mons alone? (you would need a massive strike-slip zone between them to keep OM single). Also there's no obvious age sequence from Arsia to Ascraeus and we have three giant shields instead of a chain of many small ones, so it's a very poor match to the terrestrial example. The magnetic anomalies are more on a scale with the 'fossil mountain ranges' recorded in magnetic maps of the Canadian shield (Grenville and so on - check out any mag map of North America) - not the narrow stripes that suggested seafloor spreading. So I have to say I'm not a big fan of any supposed Martian analog of Plate Tectonics.

Phil


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Ron Hobbs
post Aug 22 2012, 09:13 PM
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Thanks, OD and Phil, for filling in some of the background on this debate. Until this topic popped up here, the MGS release was all that I knew about the issue. I naively assumed that the notion of incipient tectonics was fairly well accepted. Thanks for setting me (and us) straight.

That is what I love about this site; I learn all kinds of things I would not have access to otherwise.

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paraisosdelsiste...
post Aug 26 2012, 10:12 AM
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I know and understand that the debate over plate tectonics in Mars is a very difficult one: It stopped a long time ago, the erosive and depositional processes might have erased and buried some superficial features linked to plate tectonics and also it's possible that Mars had a different kind of plate tectonics. But when someone asks me about plate tectonics in Mars, I show them this image, because I think it states my opinion better than I can do:

Attached Image


What do you think?
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