[X] My Assistant

[dburt]

Aussie - Only the big picture, I might argue. Diffusion is a function of having chemically different pore fluids above and below, not necessarily of what's in the matrix (although that may affect the speed of diffusion). In the presence of liquid water, chemical constituents dissolve and move up and down chemical gradients in the liquid, and they thereby segregate into distinct monolayers, as in the Australian lakes. Basically, if there was brine diffusion, show me the monolayers (including pure salt beds) - not a fine mechanical admixture, approximately uniform over many meters in every vertical exposure. (And I exclude the bright surface coating or efflorescence produced by upwards wicking of moisture and salts - no one is arguing that the rocks weren't once moist).

My basic problem with the brine story is that immersing the mysterious salt-sediment admixture (allegedly produced by wind erosion of granular "mudballs" off the surface of a drying playa) in brine should basically undo the mixing done by the wind and leave you with something close to the playa lake you're supposed to have started with (e.g., separate mud and coarsely crystalline salt layers). No such diffusional segregation process is evident. The inference is that the granular salty sediments, whatever produced them, were not immersed in brine afterwards. The Australian lakes, except for their acidic chemistry (easily explained by the fact that they are at the opposite exteme from Mars in terms of degree of chemical weathering and leaching), are not unusual. They are chemically "well-behaved." Meridiani is not. (In fact, it seems to be extremely naughty.) I hope this explanation helps. And keep in mind that I actually like the idea of brines on Mars!

-- HDP Don

[Doc]

Well put Burt... I must say you have an almost mystical way of peeling the multilayered Meridiani paradox.
But Im afraid its going to take more than that to make me accept your impact surge hypothesis
(No hard feelings... )
The fact that acidic water cannot exist on Mars is well... but the brine idea has a certain logic in it when it comes to explaining alien places like Mars. But it may make you happy to know that I am looking into the thing afresh...(which is partly the reason why I dont post alot these days ).

[marsbug]

This seems to have been overlooked, and it talks about ice deposits formed during the amazonian, perhaps it's old news that I missed? Anyway if there has been volcanic activity in the geologically recent past, as the article juramike linked suggests, then (IMHO) the chance of there having been habitable niches in the amazonian era take a boost.

[dburt]

This seems to have been overlooked, and it talks about ice deposits formed during the amazonian, perhaps it's old news that I missed? Anyway if there has been volcanic activity in the geologically recent past, as the article juramike linked suggests, then (IMHO) the chance of there having been habitable niches in the amazonian era take a boost.

Marsbug - Thanks for the link. No doubt there's lots of ice on Mars. What I found most interesting about that story is that to depth of a kilometer, apparently, they detected no liquid water or brine (or they would surely have announced it) - just ice. This again implies to me that the surface (and shallow interior) of Mars has been freeze-dried for a very long time - possibly since before the end of the Late Heavy Bombardment, despite episodic, highly localized brine releases later. This inference is supported by this new news article on numerous small, highly localized putative chloride evaporite deposits and their intimate involvement with cratering (3.8 billion year old age in the story) in the ancient highlands terrain. As I've suggested here before, if you want warm, habitable niches today it might be safest to look inside the long-lived giant volcanoes (as indirectly implied by that earlier article on volcanism).

-- HDP Don

[Doc]

As I've suggested here before, if you want warm, habitable niches today it might be safest to look inside the long-lived giant volcanoes (as indirectly implied by that earlier article on volcanism).

-- HDP Don

I can agree with you on that statement. Also I can agree that perhaps the sediments that we see rich in clay minerals are not necessarily the best place to look for signs of life. In the end places with past (or current) magmatic interaction could be the new goldmines.

[SickNick]

Back in the Paolo's Plunge thread, someone recently made a statement to the effect that the idea of an early wet, warm Mars has gone from a proposition to a belief. The statement made it clear that this was a bad thing -- that the concept of an early wet, warm Mars is keeping us from seeing how the planet's histopry has actually played out.

I'm responding to that statement here since I don't want to continue to hijack the other thread. But I feel the following two points must be made:

1) Mars was once warm enough (and had a thick enough atmosphere) to support flowing liquid water on its surface.

2) Mars was once wet enough for that liquid water to form well-developed river drainage systems and for enormous floods to scour thousands of square kilometers of its surface.

Those two statements aren't theoretical. Observed landforms verify them with primary, empirical evidence of river channels and catastrophic flood plains.

Those are statements of fact, not belief. My own feeling is that we must proceed from that point and not continually try and postulate a Martian history which cannot account for these proven facts.

Also, to the comment made several times that the LHB was responsible for the stripping of Mars' atmosphere, I must point out that several reputable studies have shown that the interaction between the solar wind and Mars' upper atmosphere is sufficient to have reduced an atmosphere as dense as Earth's to what we see today over the course of three billion years. And that neither Venus nor Earth seem to have had their atmospheres stripped during the LHB.

Just a few points I felt needed to be made at this juncture.

-the other Doug

What you say may well be true, but it's also misleading.

let us restate the observations:-

2a) The erosion patterns in e.g. Warrego Valles are almost impossible to produce without liquid water and precipitation (which could be snow, with basal melting trickling down snow-covered gullies)
2b) The catastrophic floods in various areas of Mars are most easily explained by Mars being WARM enough to melt subterranean ice in a once-only local event
1) Given the above, Mars must have been at least locally and transiently warm and wet enough for liquid water.

Now let's look at the rest of the context. ESA have published a very useful and compelling chronology of the role and activity of water on Mars, as seen from planetwide distributions of mineralogy:-

1- A widespread and active (but not necessarily permanent) water system producing clays - Back in the Noachian
2- A limited water system with strong acid brines producing sulphates - Back in the early Hesperian or late Noachian
3- An extended and planet-wide aridity lasting to the present day - some 3.5 billion years. Local exceptions occur associated with volcanic heating and consequent floods, but little if any chemical evidence results.

The simplest way to interpret all this is in a scenario where the stable state of Mars is arid and frigid, at almost all times. Back in the Noachian, major impact events caused atmospheric transients (lasting tens of years to thousands of years) during which the atmosphere was kicked into a metastable state with liquid water activity. Essentially, after the Noachian, no impact was big enough to cause a global ocean and rain. After the Hesperian, there was nothing left. Thisd model was originally proposed in concept form by myself but developed more carefully by Teresa Segura.

Essentially, we're looking at the evolution of Mars *as it accretes*. During THIS time, the system is energetic enough to enable liquid water (Recall that on earth, at the same time, the atmosphere was beleived to be superheated steam, or even silicate vapour! Mars is colder - there is "only" liquid water, but it's as stable on Mars as superheated steam is on Earth, imho...)

[sjbradshaw]

This is a fascinating discussion, and it makes me wonder if anyone here could offer their thoughts on the following question.

If we assume for the sake of argument that infrequent large impacts can produce a temporary warm or wet Martian environment, how long would such conditions last? In particular:

- How dense would the resulting temporary atmosphere credibly be? 0.1 bar, or more?
- What would it comprise - CO2 liberated from frozen deposits, or vaporised rock?
- What would be the process by which the Martian environment reverted to its steady state?

Thanks for any insight you may be able to provide,

Simon

[marsbug]

My uneducated guess: To produce heating over a long time or large scale an impact would need to trigger vulcanism on a global scale. So I'd think the chixelub impact, where a ten KM body hit mexico leaving a crater 200 odd km across, and maybe triggered vulcanism in the deccan traps on the other side of the earth, as a reasonable hand waving lower limit. As to how long it would last, I'd guess hundred to tens of thousands of years, but not hundred of thousands or millions unless the impact was really huge (just a stab in the dark). I doubt vapourized rock could comprize an atmosphere that would be cool enough for water, so vaporised ices and volcanic gases are the likely candidates. As the vulcanism or residual heat from a really big impact dies down i imagine the surface becomes cooler, gases making up the temporary atmosphere freeze out and atmospheric pressure drops back toward 0.01 bar. And Nick it's good to see you posting here again.

[SickNick]

My uneducated guess: To produce heating over a long time or large scale an impact would need to trigger vulcanism on a global scale. So I'd think the chixelub impact, where a ten KM body hit mexico leaving a crater 200 odd km across, and maybe triggered vulcanism in the deccan traps on the other side of the earth, as a reasonable hand waving lower limit.

---snip---


And Nick it's good to see you posting here again.

Yeah, I took a break. I lost my wife, got over it, got Cancer, got over it, got married again, still can't get over how good it is...

As for Mars, and impacts, you need a planetary-scale impact that will deposit an impact sheet AT LEAST 1 m thick. That will keep the atmosphere hot for 1 year, and the surface warm for 10 years. A 10m impact sheet is worth about 30 years in the atmosphere and 300 years at the surface, and a 100m sheet is 1000/10,000 years

But when you look at the size of impact require to acheive this, the mind boggles. Isidis and Hellas are the sort of thing we need. I think Teresa Segura failed in her effort to show that impacts on mars are important for dynamic/transient atmospheres because she statted too late in Mars time, AFTER the giant basin-forming impacts. If we go back to this time, and to the time of ultra-giant basins like the entire northern plains, then it becomes a no-brainer. Clearly, at this time, Mars had some liquid water. It probably had a lot of steam, and then a lot of rain... it was probably at this time that the water was active on Mars and did most of its doings. Later, Mars was a lot quieter, but we still see the last echoes of that early activity...

[marsbug]

Congratulations on coming through what sounds like a very rough patch Nick, and congratulations on getting married!
Vulcanism on mars would have been a lot more active at the end of the late heavy bombardment, would that not have kept at least some locales warm between, and for some time after, the giant impacts? I'm not sure when the giant basins were formed. Could a more or less continous stream of smaller impacts contribute to keeping the planet warm? I'm afraid I'm throwing ideas around wildly here as I'm not familiar with how the late heavy bombardment/final planetary accretion was structured in time.

[sjbradshaw]

I doubt vapourized rock could comprize an atmosphere that would be cool enough for water, so vaporised ices and volcanic gases are the likely candidates.

Ah, I phrased my original question rather ambiguously. I was wondering about CO2 liberated from carbonate rocks by the impact; I seem to recall a rather extreme terraforming proposal that involved very enthusiastic, er, nuclear engineering to do this.

[tty]

My uneducated guess: To produce heating over a long time or large scale an impact would need to trigger vulcanism on a global scale. So I'd think the chixelub impact, where a ten KM body hit mexico leaving a crater 200 odd km across, and maybe triggered vulcanism in the deccan traps on the other side of the earth, as a reasonable hand waving lower limit.

Sorry, but no. The Deccan eruptions started well before Chicxulub, which is proven by the fact that the iridium layer from the impact is found in one of the intertrappan beds within the Deccan traps. I think something more like the Hellas impact is probably needed.

[marsbug]

Thanks for the info tty, I was under the impression it was still being debated.

[dburt]

...As for Mars, and impacts, you need a planetary-scale impact that will deposit an impact sheet AT LEAST 1 m thick. That will keep the atmosphere hot for 1 year, and the surface warm for 10 years. A 10m impact sheet is worth about 30 years in the atmosphere and 300 years at the surface, and a 100m sheet is 1000/10,000 years

But when you look at the size of impact require to acheive this, the mind boggles. Isidis and Hellas are the sort of thing we need...

Hi Nick, I'm also happy to see you posting here again (although I've enjoyed following your occasional Mars-related comments elsewhere). I seem to have ended up agreeing with most of what you've said in the distant past, even about White Mars, except I feel that it's adequate to suppose that the "white" can be some combination of ice and salts (and of course impact-derived steam), rather than some form of carbon dioxide (not that the latter can be excluded). We met in 2001 when Knauth and I presented our low-melting salts idea at an LPI workshop.

Anyway, in response to sjbradshaw, as I understand it, and as you stated above, a major impact will volatilize nearly everything, including silicate rocks (even ephemerally separating, e.g., Si from O), but the silicate fractions will condense relatively rapidly, possibly to glassy spherules, as on the Moon. Carbon dioxide from target rock carbonates was a major vapor component for e.g., Chicxulub on Earth, but it remains to be seen if such target rocks ever occurred on Mars (probably not). The most important impact-derived greenhouse component on Mars is probably simple steam (water vapor) from impacted ice (or brine), together with sulfur dioxide from impacted sulfides and/or sulfate salts (you don't need unusual episodes of volcanism to make it). Condensation of impact-derived sulfur dioxide as ferric acid salts, and/or late oxidation of impact-distributed sulfides, could account for the mine-dump type mineralogy of the surface of Mars, without requiring acid seas, lakes, or groundwaters (which are nearly impossible from a geochemical standpoint).

Nick, I'm not sure that a Hellas-sized impact is actually required, if one accepts the Late Heavy Bombardment (LHB) as having occurred at about 3.9 billion years ago (long after initial accretion at 4.5 billion years). As suggested by marsbug, a concentrated stream of smaller impacts at the height of the LHB might be sufficient to account for the buried clays, drainage networks, and so on. I agree with you that as the LHB was tailing off, and afterwards, impacts were generally too small to yield much of a greenhouse, and, in fact, late impact debris seem to have covered up the clay minerals in most areas of Mars.

-- HDP Don

[SickNick]

Hi Nick, I'm also happy to see you posting here again (although I've enjoyed following your occasional Mars-related comments elsewhere). I seem to have ended up agreeing with most of what you've said in the distant past, even about White Mars, except I feel that it's adequate to suppose that the "white" can be some combination of ice and salts (and of course impact-derived steam), rather than some form of carbon dioxide (not that the latter can be excluded).

---snip---

-- HDP Don

Thanks Don. I also have come agree with most of what you and Knauth have been saying. With time, there is a convergence of concepts, driven by the accumulation of evidence. Most Mars scientists are coming to terms with a long-term dry and cold Mars, but that doesn't stop volatiles having an important role at some times and places. The trick is to understand when, where, and how the volatiles act.

I'm still learning...