http://www.abc.net.au/news/stories/2008/02/16/2164485.htm
http://cosmiclog.msnbc.msn.com/archive/200.../15/668749.aspx

and http://marsrovers.jpl.nasa.gov/newsroom/pr.../20080215a.html

All the more reason to search aggressively for any signs of past or present life; we need to understand constraints (and extinction factors, if applicable) as well as possible.

I used to eat a lot of salt and vinegar potato chips and I'm still alive.

Of course, Opportunity is only showing us one niche in the martian history. If there was a global sea, it would have uniform salinity and acidity, but otherwise, perhaps different basins would have different chemistry.

Yeah, I was actually thinking something very like that too, JR. Mars may well have been a bewildering patchwork of microclimes in its infancy, much more so than the Earth has been throughout its history due to the persistent ocean cover. Think it's going to be quite awhile before we can reconstruct the entire story...if ever.

99 days till Phoenix lands - maybe she'll show us something different.

I'm confident enough to say yes, if for no other reason that the terrain gets buried under CO2 snow (undoubtedly with some H2O clathrates) every year; there's gotta be some ongoing chemical alteration of the upper regolith. Suspect that we won't see shallow salty layers like we have @ Gusev, though hard to verify that prediction without mobility.

Agree about one specific niche, but it need not be an especially rare one. Five Mars surface landers, dating back to Viking, all detected abundant salts, on different areas of Mars. The highest levels may have been measured by the two rovers, but there seem to be on the order of 10% sulfate salts nearly everywhere on the dusty surface, judging from measurements made by the other three landers (and more recently, from orbit). You might not even need seas or sedimentary basins, because on any water-rich terrestrial planet where the vast majority of the water is frozen, frozen-out crystalline salts should be abundant. (Compare also Europa.) Surface evaporation of concentrated brines, "wicking" (capillarity-driven salt efflorescence) involving moisture, and sublimation of ice layers that once covered brines, probably also contributed to the surface saltiness. Impacts and the wind probably served to distribute the salts planetwide, as well as (in the case of impacts) to generate ferric acid sulfates (e.g., jarosite), although Roger Burns-type moist weathering of pulverized sulfides would also serve. Millenia of frost leaching of salts with the largest freezing point depressions (i.e., chlorides), should have left the surface enriched in those salts with the least F.P. depression (i.e., sulfates), whether or not minor quantities of sulfates were also added to the surface by later volcanism. On a basaltic planet, especially one with migrating wind-driven basaltic sands and pulverized basaltic regolith, acidic seas or lakes are extremely unlikely, as is acidic groundwater, a Chemistry 101 fact that I keep repeating (and that Roger Burns knew well). The only way acids should be able to persist on basaltic Mars is in a frozen or crystalline state (e.g., trapped in ferric acid sufates like jarosite, as Roger Burns first proposed). Paul Knauth and I published on Mars surface saltiness (sulfates vs. chlorides) well before the rovers landed (in 2002 in Icarus and in 2003 in JGR), and I recently reviewed these ideas for participants at the LPI Martian Gullies Workshop in Houston.

As a general comment, I'm not aware that the cross-bedded salty rocks at Meridiani have ever been named "evaporites" except by a few posters to this site. More precision in terminology might be appropriate.

-- HDP Don

Mars too salty for life as we know it, maybe..

Yes....but then Venus is too hot for life as we know it and Titan is too cold for life as we know it. I'm not advocating we give up hope. No one would be more pleased than me if the right niche for life on Mars exists or once did, but if I were a bookmaker I might be altering the odds I offer on any bets.

There has been a bit of "wanting to believe" despite mounting evidence against.

Balderdash. Life always has a way. On Earth we have it in hot oceanic smokers and in evaporitic desert playas and there are acidophiles and sulfate bacteria and other extremophilic bacteria.

--Bill

Yes, but did life actually begin in such extreme environments? It's one thing for it to adapt to an extreme environment, it's another to actually develop there.

Here in the UK the BBC is announcing this as "The death knell for boffins' hopes of finding life on Mars" but I'm with you, Bill, this isn't the end of the story, not by a loooooooooooooooooooooooooooong way. These are just results from two tinier than tiny areas of Mars, and there are places on Mars where conditions would have been radically different, I'm sure.

I'm taking this news with... ahem... a pinch of salt.

I feel a theory coming on...
Maybe high acid on Mars is the norm for all smaller planetary object at a distance from their stars where the metal concentration drops off and the concentration of volatiles increases. Not enough iron to bind and sequester sulfur into the core as sulfide. Thats what makes the Earth habitable its massive iron core.

Europa, Io and Titan even if they were warm enough would be sulfuric acid hell holes incapable of sustaining life. There seems to be enough indications on Europa for sulfuric acid, its just a giant tank of battery acid under that icy crust.

Maybe the habitable zone around a star not only relies on temperature but also on the iron/sulfur ratio being above a certain threshold, the further out you go the more acidic the planetary bodies become.

Ammonia, as well as many heterocyclic nitrogen compounds are actually basic. I'd expect anything with a larger amount of ammonia ices (outer solar system bodies that fomed beyond the ice limit) might be basic.

["base" in this sense = materials that suck up protons when dissolved in water, shifting the water equilibrium to favor hydroxyl ions (-OH) in solution, raising the pH and making the solution more alkaline].

-Mike

"Nasa's Mars rovers - Opportunity and its twin, Spirit - have now spent more than 1,400 days on the Martian surface. They are due to be replaced by the Phoenix lander, expected to reach Mars on May 25." - Richard Gray, Daily Telegraph

Sigh...

Do newspaper science reporters have to pass an exam to prove they actually know *****r all about astronomy and space before getting the job?

No, they don't. A fact we're reminded of every so often.

Is there sampling bias? All five landers have set down below "zero altitude". It seems like on Earth, salt has drained from high elevations to low, as it is dissolved in water and washed downslope, but it doesn't make the return trip by evaporation. So the low elevations continue to get saltier. The higher lakes in the world are usually freshwater (Titicaca, Baikal), whereas the near- and below- sea level lakes that comprise drainage basins are all salty (Dead Sea, Caspian, Aral).

So maybe the martian Eden would have been somewhere upslope like Solis Lacus?

Where would Venus fit into that theory? Isn't there sulphuric acid in those Venusian clouds?

======
Stephen

Volcanism + liquid water = acid - no matter what the orbital radius.

Yes but the amount I assume is relatively small on a planetary scale and I also that most of Venus sulfur is also locked up in its core. The temp of Venus changes the equilibrium. Dont forget we are talking salt as well and on Venus there is not much opportunity for the acid to react with the basaltic rock.

Yes but its the amounts that I'm referring to. In the inner solar system the amounts of acid and salt is relatively small and capable of being regulated by the large amount of rock and metal and as we move outwards they increase in concentration start to get out of the range that we know of as being capable of sustaining life.
My point is that the Earths iron core removes most of the free sulfur from the surface system and therefore limits the amount of salt produced.

Quite possibly, Gordan. The environment near a hydrothermal vent on the ocean floor might be quite benign compared to the early Earth's surface conditions. No lethal UV, reduced cosmic radiation, no unstable climate with large temperature swings, a ready and consistent supply of nutrients (sulfates and sulfur compounds). Acidic conditions make for mobile metal ions (like iron), which means more foodstuffs.

As I said, a virtual Eden compared to Dante's inferno upstairs.

--Bill

I will point out that, at least according to a lot of recent reports, *all* life on Earth is descended from extremophile organisms -- i.e., organisms that had adapted to conditions in which life as we know it could not have started.

At least on Earth, life is adaptable enough to adapt to *global* conditions in which it could never have begun. Is there any reason to believe that life on Mars could not have done the same thing?

-the other Doug

Yes, we could consider, in an un-chauvinistic moment, that we're living in extreme conditions now (even those organisms in Hawaii, much less Greenland). Oxygen is nasty stuff that life had to adapt to. Now I'm sucking down thousands of liters a day and loving it.

But not all versions of "inhospitable" are equally inhospitable. If life originated at a certain temperature and then adapted to survive at a given temperature X degrees warmer, that doesn't mean it could have adapted to X degrees colder.

I fondly remember an Isaac Asimov essay in which he considered about six different kinds of "life not as we know it" and postulated organisms based on chemistry applicable on the surface of Venus and Titan and other places. Those were wild possibilities, and not apt to be feasible, but is super-high salinity or low PH in the same category? Beats me.

Yes, but the LUCA (Last Universal Common Ancestor) was probably not an extremophile. At least that is the word from the geneticists.
That all extant life has extremophile ancestors is probably a result of the Late Heavy Bombardment. Only extremophiles survived, and "nonextremophiles" had to re-evolve from these.

On the other hand lots of those extremophiles ought to have been transported to Mars by the LHB and so wouldn't have to evolve there.

Just to clear the table a bit, here: do we definitively know what is and is not possible with respect to the evolution and survival potential of life? Definitely not talking about way-out stuff, here, but merely organic chemistry, which seems to provide an endless series of surprises. (Shining the Juramike spotlight into the cloud layer right now to summon The BatChemist...it's the silhouette of a double helix with Groucho Marx glasses... ) Come to that, do we have an unassailable understanding of the geological history & climatology of Mars? I think not.

Main point here is categorically ruling out life on Mars is both practically & statistically impossible, especially based on an extremely limited number of very localized samples. In fact, if Mars is indeed dead, then it will probably take at least a thousand years of intensive exploration to prove that beyond a reasonable doubt, since every conceivable ecological niche would have to be exhaustively analyzed, including possible subsurface bioenclaves. Proving a negative is very difficult; in this case, all it would take is one little bug demonstrably not of terrestrial origin (a gigantic can of worms in itself to prove, esp. since we've landed/crashed a fair amount of unsterilized hardware), to overturn the entire proposition.

Not to come off as a zealot, you understand. In my personal estimation, Mars has, at best, a 1% chance of harboring extant life, and very optimistically a 10% chance of ever having had native life at all. Still, those are way better than zero odds, and it's gonna be a bear to settle the issue either way unless we find an organism that doesn't use DNA, RNA, or anything else Earth life hasn't thought of already...

I'm hoping to read the paper before I form any strong opinions. I'm a bit surprised by all the fuss this has caused though, from what I've read it fits very well with the picture of martian history we were already building up. Three things i'd like to say are; 1) Hoping for extant life on mars has always been an against the odds kind of thing, thats what has made it attractive to me.
2) The fact that the climate went bad doesn't affect the evidence that it was once more benign, even if only for a fairly short period waaay back at the begining.
3)If mars was truly never habitable, even for microbes, it's a disapointment but not as great as some will say. Europa and ganymede both hold strong promise of oceans, the nature of the plumes of enceladus has still not been settled to my mind. In addition, we know that there is a lot to learn about the prebiotic chemistry that led to life from titan, and learning more about life here is the whole point of looking for life out there.
Does any one know how to get hold of the paper ?

Reflecting back to Mars James Lovelock's Gaia Theory (which I can buy in small doses - but certainly not the family-pack hippy-trippy "Aum" versions you sometimes meet)...

The alleged "bad climate" is surely going to be the most stable and suitable one for any extant indigenous life to maintain, if life's present. After all, if atmospheric mass is going to be lost over geological time, then life might well have to put up with the physics of living on a low mass planet and work with it rather than against it. It can only hold CO2? Then use it and vent your methane! Not much access to "water"? No problem, restrict the biomass, think bacteria-size and below. Extremophiles living in saline? A mere Earthcentric viewpoint...it could well be the environment Mars' life works best in.

I don't see this report reducing the chances of life on Mars to nil - we know life is ferociously adaptable, has survived many major disruptions to Earth's conditions. If it started (and that's just chemistry+time) then I wouldn't be ruling it out just yet.

Andy

My take on this is that whenever "experts" step forward on a subjective topic and declare some aspect of it to be "impossible", the chances of those experts being wrong go way up.

That's not to dis all expert scientific opinion, but when there are so many open-ended variables, I find it hard to accept blanket pronouncements like this.

"There is absolutely no likelihood man can ever tap the power of the atom." Robert Millikan, Nobel prizewinner in physics, in 1923

"The bomb will never go off. I speak as an expert in explosives." Admiral William Leahy

"Heavier-than-air flying machines are impossible." Lord Kelvin

"Man will never reach the moon regardless of all future scientific advances." Dr. Lee De Forest, inventor of the vacuum tube and father of television.

Well, there's something called extremophiles...
An extremophile is an organism adapted to living in physically or geochemically extreme conditions.

Think the core issue is whether life could have ever evolved on Mars given the salty surface, and my argument is twofold:

1. Do current conditions reflect conditions in the distant past? (I doubt it.)

2. Is there only one golden biochemical pathway to the evolution of life? (I doubt that, too.)

Keep in mind, we still don't know how life arose on Earth, let alone
how or under what circumstances it may have arisen on Mars. I've
seen ideas expressing that life may have started on clay surfaces,
in sea foam, on -- or in -- ice crystals and who knows how else. I
expect one day to read that life may have started in fluid-filled
cavities within salt crystals!

Well, I've had salt on my chips for years, and I'm fine...

Seriously tho, we just don't know, do we? This "Life was impossible because Mars was salty" extrapolation is based on observations of just two tiny locales. Very premature to doom the idea of martians to the history or science fiction books.

Come on Phoenix, surperise and delight us...!

Centsworth, that's an excellent point. The only thing we probably know about the origin of life on Earth is that it happened in one way due to the overall biochemical similarity between all extant organisms...and even that's open to debate, since it's possible that our particular flavor of life just won out over competitors.

Mars...who knows if, or what, or how? That's why we're looking.

Actually, what neutralizes S-rich acid is not iron (iron sulfides oxidize to highly acid iron sulfates, after all), but stronger bases such as soda (Na2O), lime (CaO), and magnesia (MgO), abundant mainly in silicate rocks such as basalt. It doesn't matter how much oxidized, acid sulfur (H2SO4, sulfuric acid) or chlorine (HCl, hydrochloric acid) was emitted, what matters is that there was enough silicate rock to neutralize the acid, producing neutral salts, such as gypsum (CaSO4*2H2O) or halite (NaCl). This is how most salts on early Earth were formed, shortly after acid degassing, and it is how most salts on early Mars were likewise produced. Earth's oceans remain relatively basic owing mainly to interactions of seawater with the basalt that makes up the sea floor, despite all of the acids that volcanoes and our civilization constantly emit into the atmosphere. In short: salty yes, acid no.

I don't see why some people expect Mars to be so different, if liquid water was present. As Knauth and I have stated in print, the ferric acid sulfates on the surface of Mars (both rover sites) probably indicate dry, cold, and salty, not warm, wet, and acid. Planets do get more volatile-rich as you go out from the sun, but these volatiles are not necessarily acid species (e.g., ammonia in the gas giants, as someone else pointed out). Note that I am not commenting on oxidation state, only acidity (although the two variables can be related), because both Earth and Mars appear to have oxidized surfaces (probably for different reasons - photosynthesis on Earth, UV radiation and hydrogen loss on Mars). I'm also not commenting on whether or not Mars has or had life, because I don't know the answer.

BTW, in 2001 I asked the late Graham Ryder of LPI what he thought at a party, and I really liked his reply: "Where are the shopping centers?" That was his droll British way of pointing that any life on Mars seems to have kept a pretty low profile. Note: his special interest was lunar geology, particularly regarding the LHB (late heavy bombardment, or lunar cataclysm, as it was also called).

-- HDP Don

Even as we speak, Oppy is parked 473 meters above the Starbucks in the *Meridiani MegaMall*.

*Open until 10. Unlimited free parking

Those are some classic failed predictions, and there are many more (which I always enjoy reading), but then we could probably generate some pretty solid blanket pronouncements, too. Things about time travel, putting a galaxy into your pocket, kids listening to their parents' wisdom, people acquiring Superman-like powers, bacteria that thrive at the center of the Sun, etc. The whole domain of post-reviewing futurology is skewed by the fact that you only have the examples of the "never" statements that were proven wrong. The ones that actually WILL hold up forever can always be nonfalsifiably rebutted with a "...yet."

Still, this looks like shaky ground for the experts. Aside from the existence proof of terrestrial life, we don't know much about the parameters of what is possible, biologically, and what is not.

JR, I'd take that one step farther and say that we know virtually nothing. One sample does not a continuum make.

If the "Pluto is/is not a planet" debate taught us anything useful by way of analogies, it's that natural things exist along contiuua, thereby complicating time-driven processes & our ability to assign labels to things. The only truly discrete objects are subatomic particles, the building blocks; variation to some degree exists at any higher order of organization.

(This might make a decent thesis topic for anybody out there looking to finish their MS, BTW; introducing some mathematical/statistical rigor into that proposition in order to prove or disprove it... )

That one has been done already .

Truly when we cannot seem to agree on a definition of what constitutes life, it is pretty arrogant to think that we can identify it, or indeed exclude it. I'm with Nprev, the probabilities remain within acceptable limits.

...And arrogant as well to think we can easily detect it.

Somewhere around in this forum was a link to a NASA study of life and the potential chemical pathways for life in exobiotic environments. [EDIT: link to article found in post 184, thread "The Surface Chemistry of Titan, link here]

The bottom line is: never say never.

A safe statement regarding the brine study on Mars would be that "the putative past environments on Mars might be difficult for many of the currently known microbes."

But as we are quickly learning, we know less about Life on Earth than we thought. Craig Ventner's recent genetic bioprospecting voyages around the globe's oceans have uncovered a huge genetic diversity previously unknown.

Here is one interview: http://www.nrdc.org/OnEarth/06sum/frontlines2.asp
(There was also a recently produced show on the Science channel that covered this voyage - definitely a must-view.)

A better statistic would be to figure how many of the currently known microbes on Earth could have survived in the past environments on Mars. Even if the answer is only one microbe species, it strengthens the claim that life could and still exists on Mars.

Since absence of evidence is not evidence of absence, proving that (microbial) life DOESN'T or DIDN'T exist on Mars will be very difficult.

-Mike

It's always hard to do meaningful statistics from a single data point. :-)

Personally, I think the most encouraging evidence for life on other worlds is that fact that it got started here so fast. Once the place had liquid oceans, pretty much, life appeared. That suggests it's pretty likely to appear again, given similar circumstances. (Claims that life came from outer space, I don't take seriously.)

On the other hand, the fact the multicellular life didn't arise until about 650 million years ago, suggests that that really is rare -- possibly unique. It boggles the mind that for over three billion years, the Earth had an oxygen atmosphere, but no plants and no animals -- just bacteria and mats of algae. in the oceans.

Anyway, like I said, reasoning from one data point is always hazardous. But I sure wouldn't bet on finding anything above the level of bacteria. On ANY world but this one.

--Greg

All the more impressive given the Late Heavy Bombardment, perhaps 100atm of hot gas above the microbes' heads, and tides magnitudes higher than the ones we're used to. Hadean indeed.


Multicellularism goes back a little further, and oxygen levels, while rising, are really quite low until around that point. Surely that's a link? Plentiful oxygen is required for increasing metabolic rates? That it took Deep Time for tectonics and life to get into a cycle where this could occur, and for the anaerobes to poison themselves off, isn't an issue for any world (ok, any world in a stable orbit within the HZ, perhaps with a stabilising moon) orbiting a star cooler than, say F5-ish - and there's got to be around 10^21 of those in the universe.

I would be startled if multicellular life occured just once out of a number that large.

Andy

The 3 or 4 billion year span from single cell to
multi-cell organisms may not indicate slim chances
of that advance occurring. It may be more a result
of frequent hits by killer asteroids which kept viable
life on Earth at the most rudimentary levels.

The same conditions would most likely occur in any
developing planetary system. But my point is that
the change from single to multicellular life may be
a simple, inevitable step which just needs to wait
for the right moment to occur. This is different from
thinking that it is an unlikely step in the first place.

IMO, anyway.

I don't just mean we shouldn't be expecting multicellular life -- I mean we shouldn't even be expecting eukaryotic single-celled organisms. If we seriously want to look for life on other worlds, we should be looking for tiny bacteria-class organisms. Based on the history of our own world, this is the best bet.

As far as life-as-we-do-not-know-it, we go from reasoning from one data point to reasoning from none. However, if we're looking for life in very low temperature environments, even if there are special low-temperature chemical reactions that could drive it, the sheer lack of energy is going to mitigate against anything large. Space Worms on Titan would have to somehow find enough energy to crawl, and I'm just not convinced that's possible. Space bacteria, on the other hand, I could easily imagine living very slowly.

That doesn't mean I think there is no chance we'll ever find anything bigger -- even on Titan. Life is full of surprises. But if we want the best shot at finding something, I think we need to figure out how to get an electron microscope out there.

--Greg

I certainly agree with that.

I think y'all might be amazed at how quickly, once we do start examining extrasolar planets in situ, such ubiquitous bacteria will fall from the heights of "There is now proof we are not alone in the Universe!" to "That bacteria is nasty -- how do we kill it?"



-the other Doug

[quote name='Greg Hullender' date='Feb 21 2008, 05:37 AM' post='109687']
It's always hard to do meaningful statistics from a single data point. :-)

It is impossible to do meaningful staistics from a single data point

Life on Earth is not a single data point. It is a case study.