"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?

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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.