All, I know this isn't the right place for this post, but I've looked around and can't find an appropriate, current UMSF forum (Doug, perhaps you could give me some guidance on establishing such) -- so here goes: I think a [the] new paradigm for Martian geology is rapidly coalescing, namely, that Mars is very much like the Earth in terms of the preponderance of water -- except that it is all frozen, and covered under a thin layer of dust/regolith! See, for example, this article:

http://www.skyandtelescope.com/news/41995902.html

Hence the "seepages" found in crater walls; hence the evidence of catastophic flooding -- the result of volcanism melting huge pockets of ice. And I am going to add my own wrinkle (probably not original): that the differentiation of Mars into a rougher southern hemisphere and smoother northern hemsphere represents something like Earth's Pangea stage, ie, the northern hemisphere is a vast frozen sea covered with a thin layer of ice.

Oops, of course I meant thin layer of dust, not ice . . .

New thread to move Glens posts in to.

And Glen - you should just 'edit' your first post, rather than replying to it to make a correction.

Doug, thanks for moving this. And Glenn, not a particularly new paradigm for many scientists. Everyone wants to emphasize similarities with Earth, but you have spotted a major difference - that the water is all or mostly frozen. This has been speculated on for a long time; it's nice to find direct proof. Freezing/sublimating the water released all the salts that were held in solution; both rovers, plus orbiting satellites are continually finding more salts. Another difference is the extreme age of the martian crust - billions of years, owing to an apparent lack of plate tectonics on Mars since then (implying the comparison with Earth's Pangea stage may not be an appropriate one). The ancient crust has preserved the record of ancient Martian impact cratering much better than on Earth; even the hemispheric division of Mars has been blamed (by many scientists) on a giant impact.

Incidentally, the northern hemisphere is just as heavily cratered as the southern one, except that it is lower-lying, and so the ancient craters are mostly buried under a thin layer of dust and ice, as that article pointed out. Orbital studies involving detailed elevation and radar have allowed the northern buried craters to be detected (see numerous articles by Herbert Frey). The very thin atmosphere means that impact cratering is still a far more important process than on Earth - small meteorites do not burn up in the atmosphere. A final difference from Earth is that the martian crust and lavas are at least twice as rich in iron as on Earth - an important difference that probably relates to the initial degree of hydrogen loss (core oxidation) during the formation of Mars. In part, this iron-rich nature accounts for the rusty red color of Mars - and presumably accounts, in some fashion, for the prevalence of shiny gray hematite (iron oxide) spherules at the Opportunity landing site.

The big scientific question regarding Mars now is not its water-rich nature, but rather how much of, and for how long, this water might have remained liquid, rather than frozen, on ancient Mars, during and just after ancient impact cratering episode that ended about 3.8 billion years ago (age assumed from dating of Moon rocks sampled during the Apollo astronaut program). I find it easiest to relate abundant evidence for early liquid water to the impact cratering episode itself (an easy way to generate lots of heat, a temporary steamy atmosphere, and layered sediments resembling those seen by both rovers), but others prefer to relate liquid water to early volcanism, an unusual and dense atmosphere, or both. Impacts and volcanism are not mutually exclusive, of course - both were occurring at at a high rate at roughly the same time, and afterwards both continued at a greatly reduced rate.

-- HDP Don

Dburt, thanks for the thoughtful summary. I think I am agreeing with you in referencing Pangea -- given the lack of plate tectonics, the uber continent never split into smaller pieces.

Was it really ever an uber continent at all? Perhaps it is merely a remnant of the original ancient crust before Mars got hit by a HUGE dwarf sized planetary object. The idea is that Mars was struck similar to how the Earth was smashed early in its history (the Mars sized object that created the Moon). In this respect, perhaps Mars is similar to Earth.

Did a larger Moon on Mars once exist, then smashed into Mars again later in its history? That possibility of a second event could give us a false date concerning early bombardment (assumed to be 3.8 billion years ago because of the Apollo rock dating). Mars is not the Moon. It is possible that there was more than one extreme event and the evidence is mounting that this may have occurred, but it is still not convincing. Occam’s razor still suggests the more simple solution.

I’m keeping my mind open because there is still so much that we don’t know about Mars. Answers won’t come as quickly as we might want. But look at the speculation of frozen water on Mars! It has taken almost 30 years for it to now become established fact. Just a few years ago, I was almost laughed at because of my suggestion there might have been large numbers of glaciers on Mars at one time. Few are laughing at that idea now.

Marsisimportant, thanks for adding the primeval collision to the overall picture -- you and Dburt have covered all the important bases, and in doing so, you have clarified for me what I was hoping to do with my original post, which was to paint a picture -- at which I will now, thanks to the infinite patience of Doug Ellison and all you other UMSF members, take another whack. To wit: I have been looking at the global pictures of Mars for some years now, and I have never been able to make sense out of what I am seeing. Yes, it is Earth's sister planet, but it just hasn't made any sense to me. But suddenly -- seeing the Hirise photo of a recent meteor strike on the Northern plains throwing out rays of ice -- it has all become clear. Imagine Earth at the Pangea stage with its seas frozen, and the entire planet covered with a thin layer of dust -- it would look very much like Mars today (allowing for the fact that the dust covering Mars is rich in iron oxide). I hope I am not beating a dead horse, I am just trying to explain my eureka moment. But maybe I'm behind the curve, and all of this has been obvious to most UMSF members for some time . . .

A picture of Mars with somewhat ubiquitous sub-surface ice seems to be emerging (for some value of "ubiquitous" yet to be firmly established, but certainly less than 1), and this is relatively new. I haven't seen any informed speculation about, or estimates at upper and lower bounds for, the thickness or volume of these layers (and would welcome some pointers, if anyone has any?) I like your "eureka moment" image, though, I just think it'll turn out to be a bit less dramatic than ocean-basin scale volumes.

There's the Medusae Fossae radar profile.

http://www.nasa.gov/mission_pages/mars/new...s-20071101.html

Imipak and Fran, thanks for the excellent additions to this thread. And I'm wondering inf anyone else out there has been as confused as I have been in trying to decipher the big picture of Martian surface geology?

On behalf of all who have joined this thread, I am adding for discussion purposes an image (with which I have taken some BIG liberties) showing 1) an early, "earthlike Mars", 2) Mars with its "seas" frozen, and 3) the seas covered with a thin layer of [red] dust -- voila, current day Mars! But I am not nearly so good a graphic artist as many of you . . .


Click to view attachment

A very interesting picture and discussion.

However, how much evidence is there really that all of the water was liquid at the same time? Would it not be possible that the effects were more local, resulting from various causes and not one 'tropical period'.

Lacking a large moon, precession, nutation, and polar motion of Mars rotational axis will probably be larger then on Earth, resulting in several cycle's of 'super seasons' imposed on the existing seasons (which are already stronger then on earth due to Mars more elliptical orbit). Area's with exposed ice around the poles might receive more solar heating due to this, resulting in the ice sublimating (increasing air pressure) or possible become liquid for a short while, however at the same time other area's might 'cool down' due to the same effect, and ice might start building up again on these area's (reducing air pressure again). So the ice would more or less shift from one area to the other and this might even be possible without a liquid phase in between??

Local effects might be vulcanism (volcanic heat might rapidly heat a layer of ice, resulting in the ice sublimating and possible a short local liquid period if the air pressure rises sufficiently locally during a short period) or impacts (same effects, local heating). So you might have local 'flood-waves' during short periods without the need for a planet-wide 'tropical period'.

How much prove do we have that we are looking at a planet-wide 'tropical period' instead of just a series of (more or less unrelated) local events?

So basically, it's Tim Parkers old Northern Hemisphere Ocean idea. I saw it mentioned in a few books, but the evidence wasn't water-tight at the time.

Glennwsmith, your map is OK ( and similar to other visualizations of this concept) except for one glaring error.. the ocean, if it existed, would be confined to low elevation areas, so you need to make its outlines fit contours, not albedo markings. The bright central part of your image, Arabia Terra, is actually highlands.

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

Geert, you are certainly justified in bringing up local constraints on ocean formation -- my simple-minded conception of a Mars ocean is like talking about "liberal" or "conservative" voters as if they have a uniform profile. And I stand properly corrected, Phil, for my simple-minded map-drawing technique. But it is the Dougmeister who has really got this thread unspooling into a nice, fat pile, with his mention of Tim Parker, the real pioneer of the northern ocean theory. I've done some quick (and belated?) research, and the theory of Dr. Parker and his colleagues is all over the web -- not to mention a lengthy discussion thereof on UMSF back in June of 2007! (And not to mention, as per Phil's comment, several scientific depictions of same.) Despite my discomfiture, the point remains that these photos of fresh, ice-penetrating craters will bring roaring back into well deserved focus the thought that oceans -- whether large or small -- lie frozen beneath them. Dr. Parker, we would love to hear from you!!!

My ears just burst into flames! (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!

-Tim.

Can I just say that I love this board?

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!

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.



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


-Tim.

Hi Tim - sorry about that, I had the order wrong. It's too long since I actually looked at Vic Baker's paper.

Phil

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.

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.

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.

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

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.

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?

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.

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'.

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.

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

The work of UMSF members has, on several occasions, risen above the amateur level to represent a real contribution to space science. I refer, in particular, to the graphic work which has appeared in national publications.

May I suggest that the question of the existence of an Oceanus Borealis represents a similar opportunity for UMSF members, and that this opportunity has both a primary and a secondary aspect?

Primary, in that question of an Oceanus Borealis does not depend so much on esoteric data such as, say, methane concentrations, but is to a great extent a question of visual interpretation. What are we seeing when we look at photos of these smooth northern basins? UMSF, with its four thousand plus pairs of educated eyes, can certainly make a contribution. (Indeed, some of the Mars imaging teams have issued a general invitation to interested amateurs to help scan their photos.)

Secondary, in that we can serve as an informed sounding board. Dr. Parker, for example, seemed to enjoy the opportunity of reviewing with us various northern basin scenarios. And, ultimately, a hypothesis which can be explained clearly and convincingly to an educated public is better than one which cannot.

Indeed, what we have with a possible Oceanus Borealis is one of those eureka! moments in science, or, more properly, the emergence of a new paradigm as depicted by Thomas Kuhn in his "The Structure of Scientific Revolutions". (Another example can be found at http://www.worldenergysource.com/articles/...uty_WE_v3n2.cfm -- a lovely instance of the primacy of an idea over the wealth and fame that may flow from it.)

To this end, I hope this thread will remain current, and posts added to it as additional findings become available, and as additional insights are gained.

In fact, I have a possible such insight of my own: Dr. Parker has cited the cobbled surfaces of the northern basin(s) as militating against the frozen ocean hypothesis; but surely someone in the professional ranks has had the idea that many of these cobbles, as on the Antarctic ice sheets, are accumulated meteorites?

(And thanks for the thoughts on relevance of Phoenix data.)

My only problem with the concept going around that the *entire* Martian northern hemisphere was excavated down a few km below mean by an enormous impact, whose basin is the entire northern half of the planet, is that I'd have to think such an impact would disrupt the entire planet, causing it to re-accrete rather as Earth and Moon re-accreted after the impact of a Mars-sized body on the proto-Earth.

How could Mars retain its structural integrity during an impact whose crater is roughly half the size of the planet? I'm not a mathematician, but it seems to me that the energies released by such an impact would have to be enough to disrupt the entire planet... in other words, I can't imagine a solid body that wouldn't come apart under such an impact, no matter the angle of impact.

-the other Doug

Doug,

There's an interesting paper by Melosh in Nature Geoscience summarizing recent work on the martian giant impact theory. see http://www.nature.com/ngeo/focus/planetary...CFcZM5QodGTJbCA The paper was briefly available for free, but apparently no longer. (But I may be able to find it on my hard drive.)

If I recall correctly, Melosh said that the energy released by the putative impacter would have amounted to "only" about one percent of the total gravitational binding energy of the planet, and that accordingly disruption and re-accretion would not be expected.

TTT

As part of an imaging project I've been planning, I've made a list of all the Mondo Big Impacts in the Solar System.
"Mondo Big" I defined as rim or feature diameters > 350 km. Most of the data on the list comes from the USGS Gazetteer.

Click to view attachment

This list is better entitled as "List of big impact features that have been preserved."

Kinda interesting on the list that in the Jovian and Saturnian system only the outer satellites have preserved craters.
And in the inner solar system, Earth and Venus are notably absent. Either they didn't get whapped (doubtful) or surface process have done a nice job of obliterating the evidence.

Relevant to this thread, the putative Vasititas Borealis on Mars fit's nicely with other basins seen on Mercury and the Moon. It's still on the big size, but not too weird when looking at the other planets.

-Mike

[EDIT: 20090504 2030 Updated coordinates for South Pole/Aitken basin]

That's an interesting observation about Jupiter & Saturn, Mike. Shooting from the hip, I wonder if the fact that both planets probably have had a significant amount of small stuff orbiting in their equatorial planes (the ring systems being mere tattered remnants of the originals) has contributed greatly to erosion of large impact features on their moons, which would presumably tend to form more infrequently and therefore also generally be older.

FWIW, I think you're spot on assuming that Earth, Venus & Mars wipe out really big craters pretty fast, although Argyre & Hellas are proportionately huge. Plate tectonics cleans up Earth rather well, and even the largest expanse of old terrain (the Canadian Shield) preserves only a few hefty ancient craters. Venus' surface looks a little like warm taffy at macroscales, and I bet that it's pretty malleable as silicate planetary crusts go over short geological timescales.

I thought that MOLA had detected a heavily cratered Northern landscape buried by a comparitively thin resurfacing layer - eolian or aqueous deposition or possibly both? If so this would indicate that even if the northern basin was the result of a very early impactor, this occurred before the LHB. So an impact origin and the later formation of a sea would not seem to be mutually exclusive events.

But the northern basin doesn't look particularly circular, nor does it seem to have the depth or the surrounding (kilometer deep) ejecta material that characterises Helles.

Relative to the current discussion, check out this picture of the Rembrandt impact basin on Mercury:

http://antwrp.gsfc.nasa.gov/apod/ap090504.html

This "mare" is clearly, to me, the result of lava flows -- and my money is still on actual H2O, though now frozen, forming the smooth surface of the northern Mars basin.

And as has just been pointed out, correctly I believe, there is no contradiction between an impact basin and a subsequent sea.

Some more modelling on the idea of early mars being cold and wet.

I have some difficulty with the concept that the current temperature conditions (cold) applied to Mars in the beginning. To put this in perspective Earth was apparently warm, then we had the snowball earth followed by continuous warmth (always areas above freezing regardless of cyclical swings) . Lots of speculation on sun activity levels, interstellar dust, tectonics etc but no definite explanation for this. So why do we think Mars has always been stable at sub zero temperatures and pass off the clear evidence of major liquid water effects as brines or short term impact phenomona?

Given the evidence of large impactors (including the one that formed Earth's moon) these, and near misses would have caused variations in orbits of the inner planets, particularly for Mars given its size in comparison to Earth and Venus. If we can accept that a Mars sized planetoid collided with Earth then we should accept that there is a possibility that it also had a close encounter with Mars which at that time had an orbit closer to the sun. Potentially such an encounter moving Mars away from the warmth and setting the other body on a collision course for Earth.

Flight of fantasy perhaps. But no more so than trying to explain the water features on Mars purely in terms of impact or brines

As I understand it we can explain the evidence of water using brines and impact phenomena at the average temperatures we see today, so why do we need to invoke some unknown force to warm the planet up?

I think this discussions been done before on this forum by people more knowledgable than me: Here and here. Have a read if you've got the time (lots of time) , it's interesting and quite heated in places!

Edit: Based on the last couple of paragraphs of this report (I don't have access to the full nature article) the significance seems to be that, in the right combination, salts found at the landing sites of the MER's and viking could depress the freezing point of water enough for a stable liquid to form at those locations. There might be some room to discuss how that gels with the theories already discussed, but we'd need to be carefull not to run the discussion into the ground or cross any lines. Doug and the other mods run a zero tolerance / benevolant dictator regime here. You'll notice one of the threads I linked above has been locked for causing the mods headaches!

That is the big problem with in our exploration of Mars. I myself took part in the 'great debate' with Professor Dburt and even though the idea that Mars was probably warm and wet in the past looked ok, I couldn't help but feel that maybe we are on the loosing side

For example, I used to wonder; if Mars was indeed warm in the past, how do we consider the fact that the solar output at that time was probably significantly less than now and probably we should be talking about a tundra Mars instead of an Earthly paradise. The announcement of a cold and wet Mars model ushers in yet another and seemingly more accurate way of how we view the martian geological record.

As for the locked topics; it was probably for the best (we would just be going in circles anyway )

Whoa! Marsbug and Doc, thanks for alerting me to the fact that the question of an Oceanus Borealis is entangled (as of course it must be) with the heated debates regarding basal surge versus water-based processes. I have been involved in that frustrating loop myself when I, along with Dvandorn and many others, remarked on the incredible layering of Meridiani. So part of my goal with this thread is to approach things from a different, simplistic angle: was there (or is there still, in frozen form) a vast ocean in the northern basin? When Phoenix landed on a sheet of ice, and when meteorites at widely spaced intervals are turning up ice, the presence of such seems likely to me. Interestingly, even Dburt advances the possibility of a northern ocean, in post #36 from the thread which Marsbug turned me on to, "Welcome Professor Brine Splat":

"Large amounts of water apparently survived in the subsurface, however, as both ice and (probably) deep brine (as evidenced by occasional catastrophic releases to outflow channels that possibly formed ephemeral seas in the northern lowlands)."

And I will now succumb to the temptation to use an emoticon:

Thanks for the emoticon, Glenn, but do you have a question? If Mars has almost always been rather cold and icy compared to Earth, owing to a much greater distance from the Sun and a paucity of atmosphere, this does not prohibit temporary surface warming (i.e., for perhaps several thousands or hundreds of thousands of years) owing to major meteorite impacts or groups of impacts, nor does it prohibit liquid water from existing on present-day Mars as concentrated brines or as very ephemeral snowmelt in low elevations containing dark (easily heated) basaltic rocks or dust. It also does not exclude local warming and brine beakouts near volcanic centers, although these centers seem to have rapidly declined in number after the end of major meteorite bombardment (the so-called Late Heavy Bombardment or LHB). Given how ice-rich Mars seems to be, soon-to-be-frozen-over lakes filling impact basins or even a temporary sea filling the Northern Lowlands could easily form following a really major impact event or series of events.

That said, 5 years of two rovers wandering across the present-day surface of Mars has as yet revealed no direct geological evidence of standing or flowing liquid water (such as a single shale bed or single pebbly stream channel) in the bedded rocks that make up both rover sites, although various interpretations have been made, entirely on the basis of preexisting expectations and putative terrestrial analogs. All the exposed fine layering at both rover sites is consistently cross-bedded, generally at low angles, and both sites contain enigmatic concentrations of generally unclumped tiny spherules (in distinct layers) and of acid sulfate salts. One site, in which most of the layering is rather coarse (breccias with abunandant lava fragments), contains a distinct horizon with silica-rich fragments, such as might originally have been produced in a boiling (easy to do on low pressure Mars) hot spring related to an impact crater or volcano. AFAIK, both sites contain abundant evidence of meteorite impacts, including evidence of very recent impacts and of actual fragments of meteorites on the surface, but neither site contains locatable volcanic vents.

I don't care to discuss further my own rather obvious and by now way over-explained (to most readers) interpretations of these highly interesting and valuable scientific observations. Occam's Razor, the Rosenthal (experimenter expectation) effect, and all that. Nuff said, although new contrary observations and interpretations remain highly welcome (send me a private message if you wish).

-- HDP Don

I'd suggest that buried ice exposed by small impacts (as seen in this LPSC paper) at low elevations might be a better source of ephemeral liquid water, as it's an idea I've taken a shine to.

Thanks. No problem with that very good idea either, although keep in mind that on very low-humidity Mars, exposed white ice or snow (alone) is much more likely to sublime (simply evaporate) than to melt. That's why I hypothesized dark rock or dust.

-- HDP Don

An small impact could do a good job of mixing dark rock and dust with ice....ok like I said it's my pet idea this month!

But, with regards to the presence of a frozen northern ocean, wouldn't a census of small craters churning up ice be a nice cheap way to map ice distrubutions at depths greater than a meter? I assume that's beyond the limits of current techniques or the ice turned up at these craters wouldn't have been a surprise! A job for someone with patience who doesn't mind combing HIRISE images of mars I think, with some follow up by CRISM to confirm that it is ice not just light toned soil .

Interesting thought. In fact, I'd be surprised if someone hasn't already submitted a proposal to NASA to do something very similar (not that I've seen one yet). If not, someone (not me!) may well do so now that you've posted that excellent idea. (Sometimes you just gotta love academia...)

-- HDP Don

A press release from Prof Vincent Chevrier (who's been known to hang out on BAUTforum and answer questions on the Phoenix mission), whose university of Arkansas group do a lot of work simulating conditions on mars.

Thanks for posting the link Marsbug, it has all been very quiet on the Phoenix results analysis front. But there is a gap between between 'potential' to exist and 'do' exist. The article doesn't make clear whether the Mg perchlorate brine was introduced to the experiment, or if it formed naturally from ice deposits in the in the simulated martian environment of pressure / temperature / atmospheric composition and regolith. As Vincent has rightly pointed out elsewhere, the contentious 'droplets' on the lander legs do not prove the existence of brines on Mars, but are (whatever they may be) the result of the alien environment created by the landing and operation of Phoenix. Introduction of a formed brine to an experiment has the same caveat and the use of 'potential' in the article could reflect Vincent's normal and laudable, conservative approach. The TECP results did not provide any evidence of the development of films or brines. That doesn't mean they are not there - but it does reduce the likelihood.

I suspect it was introduced to the chambre to, but I'll ask. For anyone following this topic we're talking with Prof Chevrier here.

The evidence doesn't point to the phoenix site being rich in brine, but if a brine formed from components present at the phoenix site can be stable under accurately reproduced conditions then, given the size of the martian arctic, I'd bet my favourite coat (and it's a very nice coat, if a bit matrix-esque for every day use) that brines do occur, even if only rarely.

There is another thread, here, where we were taking over the formation of brines with Hanna Sizemore, a phoenix team postdoc. She is adamant that even under ideal conditions the most liquid water you'd see at the phoenix site is a few monolayers. However she was fending off talk of liquid droplets on the landers legs, and even open pools of brine, so she might be willing to go as far as 'ten monolayers, in the right spot under the best conditions imaginable' or similar if she doesnt feel like the only skeptic in the room. I hope there's room in the martian arctic for a few exceptional microclimates where brine can form in detectable amounts, becuse I reeally like that coat!

It seems that stable brines can exist on mars, using solutes available at the phoenix landing site, and at the MER's sites and the viking 1 site (see link on post 40), and there are reserves of water ice at lattitudes as low as 45 degrees north (see link on post 44), so I'll eat the coat if there aren't a few damp patches up there from time to time. It's leather so I'll have to get a big tenderiser