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Earthlike Mars?
tim53
post Apr 7 2009, 09:15 PM
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QUOTE (Phil Stooke @ Apr 6 2009, 11:42 AM) *
Doug, the first person I am aware of to promote this idea of a northern ocean was Victor Baker (U. Arizona). He called it Oceanus Borealis, I think. There was a paper in Nature about it. Tim Parker mapped possible shorelines of that ocean.

Phil


My ears just burst into flames! biggrin.gif (actually, a friend told me about this thread).

No, Phil. Vic Baker's work post-dates and is based loosely on mine...

"I started out as a child"...

Seriously, my own ruminations about a possible northern plains ocean on Mars began in 1985. Baerbel Lucchitta of the USGS and Heins-Peter Jons of Germany and I were looking at the same curious plains boundaries around the northern plains and interpreting them somewhat differently, but as indicating an ocean at that level of some sort or other. Mine was happy and "tropical" (as described above), with waves responsible for the erosional and arcuate constructional features along the margin. Lucchitta's was frozen over, with comparisons made with morphologies she saw around the Antarctic coastline. Jons' described his ocean as a "mud ocean", with the margins being flow fronts of freezing mud transgressing up the margins of the plains as catastrophic flooding dumped water and sediment into the plains.

With all the new high resolution data available now, I'm looking at the problem anew. Instead of a tropical early Mars, I think it's more likely that the planet has always been cold, modulated by pulses of greenhouse warming in a thicker atmosphere and possibly by higher internal heat flow. Most (but very interestingly not all) of the features I mapped as shorelines based on Viking data appear to exhibit debris-flow or even lava-flow front morphologies. But it's very interesting to note that these boundaries are still elevated, sometimes by hundreds of meters, with respect to the plains immediately interior to them. Tens or even hundreds of millions of cubic kilometers of water is "easier" to get rid of than the equivalent volume of lava, so I think it's more likely that these are some sort of ocean shorelines rather than volcanic plains margins.

I think it's likely that, if Mars had an ocean, that it was ice AND debris covered most of the time (not just dust, either, because the northern plains surface is rather rocky in MOC and HiRISE images). Also, if the marginal features are shorelines, Mars has lost a lot of its original water inventory over geologic time.

...subject to revision! cool.gif

-Tim.
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lyford
post Apr 7 2009, 10:47 PM
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Can I just say that I love this board? smile.gif


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glennwsmith
post Apr 8 2009, 04:44 AM
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I would like to second Lyford's point, and add my own expression of gratitude to Dr. Parker (Tim) for his post, especially appreciated given the understanding thay guys of his stature can't just rattle on like amateurs such as myself! Speaking of which, there are dozens of things I would like to say, but I will confine myself to one item at the moment. I have downloaded and read the brief article cited by Sky and Telescope, and it makes the point that, although several models confidently predict the presence in the Martian regolith of "pore-filling ice" which is a natural result of the inhalation and exhalation of atmospheric water vapor, "The ice exposed at this site [the one with the apron large enough to fill a CRISM pixel?] is not pore-filling ground ice but rather is relatively pure and is at least several cm thick." Oceanus Borealis ?!?!? Speaking for myself, Dr. Parker, but probably expressing a common sentiment among us UMSF members, please do not feel that you must respond tit-for-tat to our meanderings. We who are not on Mr. Olympus are pleased to think that you might be amused to follow from afar the enjoyment we mortals have in passing around the golden apple you have dropped in our midst!
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tim53
post Apr 8 2009, 02:03 PM
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QUOTE (glennwsmith @ Apr 7 2009, 08:44 PM) *
"The ice exposed at this site [the one with the apron large enough to fill a CRISM pixel?] is not pore-filling ground ice but rather is relatively pure and is at least several cm thick." Oceanus Borealis ?!?!?


It might be tempting to interpret these findings as "proof" that the vestiges of a frozen ocean lie just beneath the surface at these locations, but as the article points out, there are other reasonable explanations for near-surface ice - even pure ice that don't require former standing water.

QUOTE
Speaking for myself, Dr. Parker, but probably expressing a common sentiment among us UMSF members, please do not feel that you must respond tit-for-tat to our meanderings. We who are not on Mr. Olympus are pleased to think that you might be amused to follow from afar the enjoyment we mortals have in passing around the golden apple you have dropped in our midst!


I'm just a poor, humble country planetary geologist, lost in the Big City! biggrin.gif


-Tim.
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Phil Stooke
post Apr 8 2009, 09:33 PM
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Hi Tim - sorry about that, I had the order wrong. It's too long since I actually looked at Vic Baker's paper.

Phil


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... because the Solar System ain't gonna map itself.

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NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain)
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ngunn
post Apr 8 2009, 10:29 PM
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Tim Parker I'm really delighted you're here. I always believed in those shorelines, even when it turned out they aren't level now and even though their morphology is quite unlike terrestrial shorelines.
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Geert
post Apr 9 2009, 12:19 PM
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QUOTE (tim53 @ Apr 8 2009, 05:15 AM) *
But it's very interesting to note that these boundaries are still elevated, sometimes by hundreds of meters, with respect to the plains immediately interior to them. Tens or even hundreds of millions of cubic kilometers of water is "easier" to get rid of than the equivalent volume of lava, so I think it's more likely that these are some sort of ocean shorelines rather than volcanic plains margins.


I'm an absolute amateur in this so hopefully this isn't a too dumb question: but if these are ocean shorelines, does this imply that the water had to be liquid at that (or any other) time? What happens if the lava flows at the time just ran into ice instead of water, would we see the difference?

Giving the precession of the rotation axis, moving fields/glaciers of ice seem to my simple mind the easiest answer, the ice caps wonder around the surface pending the direction of the rotation axis at the time, without ever resulting in large liquid oceans. Ice sublimates in one spot and builds up again in another with at the very most only very short local periods of liquid water (due volcanic activity or impacts).
In an other threat on this forum we discussed already the theorie that the deposits we see at Meridiani could have been formed inside ice fields instead of in liquid water, so instead of a shallow liquid ocean the area might also have been covered by an icefield which later disappeared.
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tim53
post Apr 9 2009, 06:17 PM
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QUOTE (Geert @ Apr 9 2009, 04:19 AM) *
I'm an absolute amateur in this so hopefully this isn't a too dumb question: but if these are ocean shorelines, does this imply that the water had to be liquid at that (or any other) time? What happens if the lava flows at the time just ran into ice instead of water, would we see the difference?

Giving the precession of the rotation axis, moving fields/glaciers of ice seem to my simple mind the easiest answer, the ice caps wonder around the surface pending the direction of the rotation axis at the time, without ever resulting in large liquid oceans. Ice sublimates in one spot and builds up again in another with at the very most only very short local periods of liquid water (due volcanic activity or impacts).
In an other threat on this forum we discussed already the theorie that the deposits we see at Meridiani could have been formed inside ice fields instead of in liquid water, so instead of a shallow liquid ocean the area might also have been covered by an icefield which later disappeared.


Not a dumb question at all. Ice has a tremendous heat capacity, so it's even possible that the surface (and the margins that I interpreted as shorelines) are plains lavas that flowed out over an entirely frozen ocean, and that as the water was lost over geologic time, the flows interior to the margins simply settled. Some melting and steam production would have occurred, of course, possibly explaining the abundant cones that many have interpreted as pseudocraters, but that others (myself included) interpreted as pingos.

-Tim.
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stevesliva
post Apr 9 2009, 07:45 PM
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QUOTE (ngunn @ Apr 8 2009, 06:29 PM) *
Tim Parker I'm really delighted you're here. I always believed in those shorelines, even when it turned out they aren't level now and even though their morphology is quite unlike terrestrial shorelines.


When the ice sheets on Earth retreat, the underlying crust springs up somewhat. If an entire ocean-size sheet on Mars sublimated, the crustal relaxation wouldn't necessarily be even. Nor would it necessarily be analogous to Earth, because a mantle might be necessary. I just mean to throw out the point that the elevations around that amount of mass might change once it disappears.
http://en.wikipedia.org/wiki/Post-glacial_rebound

Of course it's also interesting to think along the lines of the hemispherical elevation / cratering dichotomy as indicating that there wasn't a total rebound.
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ngunn
post Apr 10 2009, 12:57 PM
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There was a nice paper that we discussed in an earlier thread which proposed polar wander caused by the growth of the Tharsis bulge as the main mechanism for disturbing the gravity equipotential from where it was in oceanic times. I'm sure somebody has the reference to hand.

EDIT Here:
http://www.google.co.uk/url?q=http://www.s...gv0n5_UnwNJ0W6g
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marsbug
post Apr 18 2009, 12:26 PM
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Reading this paper, which i'm sure most people here already have, the thought has occured to me that occasional exceptional events , like small meteorite impacts , could bring preserved ice to the surface in areas where it would not ordinarily be stable, and that this ice might in a smallest of ways melt (short lived thin films on rocks in the debris field etc). Over bilions of years, could events like this account for some of the chemical evidence we see of liquid water on mars? That could have some bearing on theories like an ancient northern ocean.


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centsworth_II
post Apr 18 2009, 06:41 PM
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QUOTE (marsbug @ Apr 18 2009, 08:26 AM) *
...this ice might in a smallest of ways melt (short lived thin films on rocks in the debris field etc). Over billions of years, could events like this account for some of the chemical evidence we see of liquid water on mars?

I wonder what the relative contributions to water-mediated changes in mineralogy are of:
1) Hot steam released by the initial explosive impact
2) Lingering sub-surface water/mud created by the impact
3) micro-films as part of an ice-rich environment equillibrium

I wonder if the impacts add much to the changes caused already by near surface ice. There was evidence of water films at the Phoenix site as part of the normal equilibrium between ice, soil, and atmosphere. Why would the same films not exist in regions of near surface ice at lower latitudes even without the impacts?
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marsbug
post Apr 19 2009, 09:52 AM
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Isn't the phoenix data relating to thin films of water kind of ambiguous? There were some things, like soil stickiness, that could be evidence for thin water films, but the one sensor that would have given an unambiguous answer, the TECP, told us the soil was bizarrely dry considering it was sitting on a slab of ice and the humidity in the air above could reach 100%.

I think that the effect small ice exposing impacts would have on Martian soil and rock would depend on how frequent they are. Ice exposed on the surface at low latitudes will be more active than ice sequestered a meter or so below. If small impacts are frequent then they might up the overall rate of water activity at the surface.


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Geert
post Apr 19 2009, 12:34 PM
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QUOTE (marsbug @ Apr 19 2009, 04:52 PM) *
Isn't the phoenix data relating to thin films of water kind of ambiguous?


I'm an amateur in this, but I still think those TECP readings are among the weirdest data Phoenix has been throwing at us, and with all the talk about water films on the lander etc I haven't seen any theorie which seems to explain those TECP readings. There is still a lot we don't know.

Getting back to the 'warm and wet Mars', I'm still wondering whether we have any data which absolutely requires a long period with large liquid 'oceans' on Mars, also given the fact that it now looks like mineral deposits can also be formed inside ice fields. I can imagine there might be short 'floodwaves' and such due to vulcanic activity or large impacts on (surface or sub-surface) icefields but it's still a big step from there to an 'earthlike mars'.
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Fran Ontanaya
post Apr 19 2009, 05:17 PM
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They'll need to reproduce the TECP results and see what happens in that clay + salts + iron oxides + water solution. It looks like a funny mixture to do electric experiments with. tongue.gif

A quick Google search gave me this, which I don't know if it may be related:
http://soil.scijournals.org/cgi/content/abstract/67/2/518
http://www.agu.org/pubs/crossref/2006/2005WR004590.shtml
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