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Italian magazine claims Phoenix contaminated Mars with terrestrial bacteria
marsbug
post Sep 3 2008, 07:08 PM
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Well this conversations been done to the death on every space forum I've ever looked at, so I won't post again on this thread. The main counter-arguments I'd give you for a near surface habitable zone are:

1:Low temperature bacteria I've covered in the links in my last post, they are actually quite common in some places and survive of tiny amounts of water too contaminated with salts to freeze.

2: The atmospheric pressure at the phoenix site is usually above the triple point pressure for water, and any water present at -20 ( which would need to be saturated with a natural antifreeze such as sodium chloride salt) would have a vapour pressure so low it might persist even below that. The pressure needed to give pure water a liquid phase is only 6.7 millibars, and that can be provided by any atmospheric gas, so the absurdly low partial pressure of water in the martian atmosphere doesn't affect the argument. Although in dry air water will evaporate faster it can still form a liquid phase, and at martian polar temperatures I guess evaporation rates would be low even in bone dry air.

3:Most bacterium would be well protected from UV radiation by only a millimetre of Martian regolith.

That leaves whatever chemical nasties might be lurking in the soil, and high energy radiation like cosmic rays. For an example of a species that can survive several extreme conditions at once, including dessication, radiation, and oxidising chemicals I give you the absurdly tough Deinococcus radiodurans, probably the best know polyextremophile but not the only one!

I will point out myself, before I'm embarrassed by someone doing it for me, that even if a microbe might survive on mars if introduced to the right spot, conditions may well still be to harsh for it to grow. Hence the critter wouldn't be able to 'go' anywhere, however as some microbes can metabolise and synthesis proteins at -15 deg c, a warm midsummer day at phoenix's location, I wouldn't rule out very slow reproduction entirely.

Or as I said above, it's right on the edge of possibility, but we've been surprised by micro organisms before...

Edit: I'm sure I've read that there might be a habitable zone in Venus upper cloud layer, but I can't find the article, I'll post a link for you If I can find it.


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gallen_53
post Sep 3 2008, 09:44 PM
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QUOTE (marsbug @ Sep 3 2008, 07:08 PM) *
Well this conversations been done to the death on every space forum I've ever looked at, so I won't post again on this thread.


You're right, it has been done to death and I'm bored with it. I'll just mention that Deinococcus radiodurans accomplishes its resistance to radiation by having multiple copies of its genome and rapid DNA repair mechanisms. If the bacterium is frozen such that its metabolism has stopped then the radiation damage just accumulates. I don't know if the experiment has ever been performed but I suspect if deinococcus radiodurans is irradiated while frozen then it dies.
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jmknapp
post Sep 3 2008, 09:59 PM
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You could add:

5. What does it do for food?

I followed the link to the -40C organism & there was something about one cell division every 100 years.

There's a question of whether the metabolic rate (repair processes, etc.) can keep up with spontaneous damage.


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gallen_53
post Sep 4 2008, 12:35 AM
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QUOTE (marsbug @ Sep 3 2008, 07:08 PM) *
I'm sure I've read that there might be a habitable zone in Venus upper cloud layer, but I can't find the article, I'll post a link for you If I can find it.


There are altitudes on Venus that border on comfortable, e.g. at 56 km, the pressure is 0.46 bar and the temperature is 18 deg.C. Unfortunately that altitude is in the middle of the sulfuric acid clouds. One could counter argue that there are microbes that LIKE sulfuric acid, e.g. archaea acidophiles. However Venus also has strong atmospheric convection and the whole atmosphere eventually gets convected down to the lower depths where nothing living could survive. This sort of argument also holds for Saturn and Jupiter (atmospheric jellyfish are not really feasible).
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mike
post Sep 4 2008, 01:56 AM
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Nothing's feasible until it happens.
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dvandorn
post Sep 4 2008, 05:22 AM
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No, Mike -- feasibility, by definition, is a projection of what is not only possible but actually achievable, based on your best information. Once something happens, feasibility is a dead concept for that phenomenon.

As for life processes, we're going to have to start thinking outside of the box in order to make any major progress in this area, I think. Life sciences are (rather necessarily) very terro-centric right now. For example, even our Martian life experiments all look for organic compounds, and if we don't find any, we state assuredly that there is no possibility of extant life.

Instead of making the (almost definitely false) assumption that any and all life forms in the universe will *always* be made of what we recognize as organic compounds, that it will *all* be powered by ADP-ATP chemical reactions, and that it *all* will require liquid water and free oxygen to become abundant, maybe we need to start asking things like:

What alternative chemical engines to ADP-ATP can be successfully hypothesized?

What other compounds than classic organic compounds could support life processes? Does silicon have enough chemical reactivity to produce living tissues? Does sulphur?

Completely regardless of its chemical composition, what do life processes *do* that we can identify from probes? *Must* it respirate oxygen? *Must* its internal tissues be water-rich? *Must* it reproduce, and how often?

I know some people have been trying to address these issues for decades -- and yet, we still see Mars probes that are designed to look for organic compounds, on the theory that life *must* incorporate the same compounds it does on Earth.

I personally think that one of the first non-terrestrial forms of life we will find will be composed of something other than organic compounds, and all of the textbooks will need immediate and thoroughgoing rewrites!

smile.gif

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Shaka
post Sep 4 2008, 07:06 AM
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OK, oDoug, we're all dying to see your detailed proposal for a Mars probe designed to test for these 'alternate' life forms.
Meanwhile, along with our friend Willy of Ockam, we have no alternative but to proceed along these trite paths of inquiry.
(Willy has the funding agencies in his hip pocket.) cool.gif


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dvandorn
post Sep 4 2008, 03:48 PM
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Well, Shaka -- just go ask all of Willy's friends who figured all they had to do to reach the Moon was to build a big enough balloon how their assumptions are doing for them these days... rolleyes.gif

-the other Doug


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Shaka
post Sep 4 2008, 08:17 PM
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If this were a Science Fiction forum, this issue would offer endless possibilities for heart-felt wrangling, Doug.
But as UMSF professes to be based on science fact, it's not worth wasting the bandwidth, so I'll drop out.
By all means take the last word, and shoot a few more straw men in the process. cool.gif


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tedstryk
post Sep 6 2008, 10:10 PM
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I think the source is questionable as well. I mean, it would be like a scientist in the U.S. going to the New York Times or Newsweek to make their claim instead of a scientific journal (or even a press releasefrom their institution with a paper to follow). Yes, sterilization isn't perfect, but I think this is really overhyped.


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hendric
post Sep 8 2008, 05:58 PM
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QUOTE (gallen_53 @ Sep 3 2008, 11:31 AM) *
I might add that a similiar argument could be invoked for life on Venus, i.e. it's deep under the surface.


Dumb question, but how would the surface temps be lower than the average atmospheric temperatures above? I understand the heat in the atmosphere comes from the Sun, but wouldn't that "cap" prevent temps below it in the subsurface?


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Juramike
post Sep 8 2008, 06:31 PM
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QUOTE (hendric @ Sep 8 2008, 01:58 PM) *
Dumb question, but how would the surface temps be lower than the average atmospheric temperatures above? I understand the heat in the atmosphere comes from the Sun, but wouldn't that "cap" prevent temps below it in the subsurface?


You are right, the temperature of Venus's subsurface would be "beyond hellish". But the high pressure might allow critters to have some sort of metabolism in a liquid (which one?) phase due to the high pressure.

Some extreme thermophiles on Earth can live above 100 C as long the pressure is enough to prevent boiling. Strain 21 can survive (and multiply) at autoclave temperature/pressures (major "Oh crap!" revelation for sterilization techniques).

Article on Strain 121 here (yet another wonderful thing from the Puget Sound region)

The upper limit for DNA-based life is thought to be around 150 C, due to breakdown of DNA and enzymes (folding of tertiary structure and all that). A biochemistry based on "harder" linkages and "harder" structure holding features (i.e. no wussy hydrogen bonds or cysteine-cysteine linkages) might be possible at higher temperatures.

Wikipedia/Hyperthermophile

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Juramike
post Sep 9 2008, 08:12 PM
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I realize I'm treading a thin line here, but this article was just too interesting and relevant to the discussion to pass up:

According to the article, some tardigrades (water bear) exposed to vacuum, cosmic radiation, and UV radiatoin in a low orbiting satellite survived and were able to reproduce on return to Earth.

So, yeah, transfer, survival in space, and reproduction if the right niche were found, is possible at least for these critters.

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ZenDraken
post Sep 9 2008, 10:43 PM
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QUOTE (dvandorn @ Sep 3 2008, 09:22 PM) *
Completely regardless of its chemical composition, what do life processes *do* that we can identify from probes? *Must* it respirate oxygen? *Must* its internal tissues be water-rich? *Must* it reproduce, and how often?

-the other Doug

One thing we can look for is out-of-equilibrium chemistry. An example is the molecular O2 level in Earth's atmosphere, which is driven by plant respiration. Absent biology it's difficult to figure out how natural processes could sustain a 20% oxygen atmosphere. And forgive me if I'm wrong about this, but as far as I know you don't generally see oxygen floating around all by itself when there's energy and plenty of other stuff it can combine with.

Another example would be Titan's abundance of methane. By no means am I claiming this is evidence of life, but out-of-equilibrium chemistry could be a "flag" for possible life or life-like activity.
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Juramike
post Sep 10 2008, 03:33 AM
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To get back to the original speculative claim for bacterial contamination from Earth...

IF life is ever detected on Mars, it will require a bit of detective work to determine if life originated on Mars, was inoculated from Earth in the distant past (big impacts on Earth would've splatted some stuff around the solar system), or might've even been inoculated from a recent mission.

If it's an alien biochemistry that's detected (how?), it's a slam-dunk that we didn't do it.

If it's DNA-based stuff, we'll have to do a lot of work to confirm it wasn't instrument contamination, or contamination from a "clean" spacecraft (or a dirty one either!). From articles above, it is "possible" that spores or dormant critters could survive long enough and lay dormant long enough that they could be a possible contaminant in a later experiment. (Although bonus: anything with DNA-repair mechanisms to be able to survive radiation exposure probably wouldn't have a high mutation rate - I'd think a quick genetic check with "usual suspects" would determine if it was originally terrestrial.)

So I'll give the article a "remotely possible" and remember to save any future backflips for detecting martian life for after the DNA results are in.

(Was Huygens sterilized?)

-Mike


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