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[Quixote]

KennyR kibitzed:

Nope, it's a matter of chemistry. At the temperature ranges where water could be used as a solvent for life (0-100C of course), green chlorophyll happens to be the most efficient chemical for photosynthesis. There are other kinds - brown, red...but these are a lot less efficient and are used by plants that don't have any other choice, like deep seaweeds.

;-) Ken, there are trees near my house that are purple. The color may be due to other elements in the leaves besides the chlorophyll, but the point is that they don't look green to the eye, or camera.

[Quixote]

Cecilia chided:

unless something can hybernate for millions of years and if you drop some water on it suddenly wakes up, we ain't seein' no martains.

;-) There have been cases of that happening on Earth. Microorganisms captured in amber for millions of years springing to life once the appropriate environmental conditions were restored.

[cecilia]

I didn't say it was impossible, just that for me to believe anything I need proof.
Being Sceptical is rational.

[Speelgoedmannetje]

Quixote wrote:
;-) There have been cases of that happening on Earth. Microorganisms captured in amber for millions of years springing to life once the appropriate environmental conditions were restored.

hum, I thought that evidence was proven false...
that earth microorganisms could have penetrated it.
With the ability of microorganisms to survive everywhere, life could be found on the moon either, since we have been there

(btw, Quixote, do you got something in your eye? -> ;-))?

[Quixote]

@ Cecilia:

;-) That's fair. I'm a bit of a skeptic, myself.


@ Speelgoedmannetje:

Nope. There is nothing in my eye, but thanks for your concern.

[ivier]

Things needed for life on Mars...

Surface :
Warmth - Gets upto 86 degrees F at the eguator around noon (mars time ofcourse). Plenty warm enough, life would just have to hibernate when it gets to cold.

Liquid Water - Areas where the martian atmosphere are higher then normal go above the 'tripoint', where liquid water can exist, though in a smaller tempreture range then earth, in these areas, water can remain liquid between 0 - 10 Centigrade. Areas where the atmostphere would be thicker include deep craters, and massive canyons.

Light - Mars has plenty of light on the surface

Underground:
Liquid Water - Mars is covered in a permafrost that goes very deep into the planet. this permafrost is mostly ice. Mars seems geothermally dormant, but looks can be decieving, unlike earth which 4.8 billion years ago got smacked by a small planetoid, which knocked by a rather sizeable chunk into orbit, and provides enough stress on our crust to keep it thin. Mars has a normal thick crust like most other terrestrial planets. But that does not mean it's asleep, it just means that events happen less often, but on a much larger scale, thus Olympus Mons. So in the deeper parts of the martian crust it is likely warmer, possible with huge ungerground rivers, lakes, and maybe even oceans.

Warmth - see above

Light - we already know that life does not need light

Under the icecaps:
liquid water - liquid water needs 2 things, pressure and heat. the more pressure you have, the less heat it takes.
The martian icecaps are huge, and express a great deal of pressure on the lower parts of the icecap. It is not inconcievable that the pressure under the ice could be great enough, to compress the ice into liquid water, and if theres even one tiny geothermal dome or vent under the ice, it's pretty much assured.

Warmth - having warth is well and good, but life does not actually need it. Seeing as how life lives on or in every continent on earth. Some forms of algae actually live IN artic ice, melting it as they need it, by excreting antifreezes.

Light - life does not need light, only energy, which can come so many ways.


Summary:
Despite Mars' harsh conditions, and the obvious fact that the surface is not infested with martian life, the conditions are there for life to exist across large expanses of the planet. Some are more likely then other to harbor life. Most will be microbial, but maybe some will be large enough to see, and maybe even crawl across the surface. The trick to finding this life, is finding where the conditions exist for the life, and waiting to see them wake up.

AfterThought: It is often stated, that mars is too small to sustain a sizable atmosphere neccessary to sustain a living planet. I believe this to be wholey untrue, but rather, that mars had it's atmosphere destroyed by a very massive impact, after most of the free material in the solar system that could replinish it's atmosphere had dissipated. the evidence is in the southern hemisphere, a crater 6 miles deep. The majority of all life on mars would have parished shortly after this impact, but the oceans would take a long time to evaporate and snow down onto the poles. Life during this time would have been adapting to a collapsing ecosystem, finding nitches where ever they lie. These lifeforms could possibly still be there today. They would likely be so fragile, they the very act of discovering them could kill them. We must tred cautious in our exploration of Mars, and hope we find life, but also that it remains living after we find it.

[KennyR]

Quixote wrote:
Ken, there are trees near my house that are purple. The color may be due to other elements in the leaves besides the chlorophyll, but the point is that they don't look green to the eye, or camera.

Wrong, they do - to a spectrographic camera. Those chlorophyll lines will be there and strong. Mars has no such lines. Therefore, Mars has no photosynthesising life.

[Karlos]

AfterThought: It is often stated, that mars is too small to sustain a sizable atmosphere neccessary to sustain a living planet. I believe this to be wholey untrue, but rather, that mars had it's atmosphere destroyed by a very massive impact, after most of the free material in the solar system that could replinish it's atmosphere had dissipated. the evidence is in the southern hemisphere, a crater 6 miles deep.

I'm not sure about this, but it could be true. However, the reasons given for mars' inability to sustain a dense atmosphere aren't invalid even if the past calamity you suggest is true.

Firstly, if you determine the mean speed of lighter gases such as nitrogen and oxygen for the upper end of the martian temperature scale, you find they are quite close to escape velocity. That's not to say they simply escape into space since the atmosphere isn't warm enough overall. However, if mars was warmed, as is central to so many terraforming ideas, this might be a problem ;-)

Secondly, there is no significant magnetosphere around mars. This allows the solar wind to erode the upper atmosphere unchecked.

Thirdly, even if mars had the same mass of atmosphere as earth, the surface pressure would not be nearly as great simply because the gravitational pull is less.

All that aside, I agree. If there ever was life on mars earlier, I expect it would still be found here and there, simply because once established it's very difficult to eradicate :-)

[KennyR]

AfterThought: It is often stated, that mars is too small to sustain a sizable atmosphere neccessary to sustain a living planet. I believe this to be wholey untrue, but rather, that mars had it's atmosphere destroyed by a very massive impact, after most of the free material in the solar system that could replinish it's atmosphere had dissipated. the evidence is in the southern hemisphere, a crater 6 miles deep.

The atmosphere of Mars isn't thick for one reason - solar wind. Because Mars is so small, its iron core cooled and solidified a long time ago. The magnetism it generated that was protecting the atmosphere disappeared, and the solar wind stripped off what remained of the atmosphere.

It's the eventual end of all rocky planets, although it happens to the smaller ones (or the low-iron ones) first. Earth really is quite exceptional in every way.

[blobrana]

Yea this is true...
The core has cooled down, (although not quite solid) and the protective magnetic shield has gone...

Impacts would have blown away parts of the atmosphere (and planet) into space, but they also (in the early bombardment era) brought water, and frozen gases etc to the planet surface.

The inner planets all started out completely molten, so any water or gases that we find on the planets today have been transported there by comets and asteroids...
(Quite remarkable, when one looks at earth`s oceans...) :-o

[Karlos]

Quite remarkable, when one looks at earth`s oceans...

It seems we weren't the only planet to be awash with water.
Studies of the Deuterium to Hydrogen ratio in the water vapour in Venus' upper atmosphere suggests that an oceanic quantity (ie comparable to the total volume of earths oceans) simply boiled away at some point in it's history.

The ratio of the heavier duterium isotope is much higher there than here.

-edit-

Thinking on the solar wind issue, whilst I don't disagree (as I already posted) the solar wind is eroding it, I am curious as to the extent.

Assuming the solar wind flux/unit area diminishes as 1/(r*r) [it should do considering a constant number of particles emitted with spherical symmetry], given the orbital semimajor axis of mars is about 227 million km compared to earth's 150 million km, so the intensity of the solar wind (per unit area) relative to earth is

F = 1/(r'*r') [where r' = 227/150] = 0.43

....assuming no other losses.

Given mars' smaller radius (about 3390km verus earth's 6370), the total sunward side of mars is exposed to:

T = F * (R' * R') [where R' = 3390/6370] = 0.43 x 0.28

= 0.12

So, a very crude guess that mars is exposed to approximately 12% of the total flux of solar wind we get.

Now, given venus also has no appreciable magnetic field and is exposed to much higher levels of solar wind than mars (given its larger and closer) and retains a vast atmosphere, how much damage to mars' atmosphere is the solar wind producing I wonder?

[KennyR]

Karlos wrote:
Now, given venus also has no appreciable magnetic field and is exposed to much higher levels of solar wind than mars (given its larger and closer) and retains a vast atmosphere, how much damage to mars' atmosphere is the solar wind producing I wonder?

Venus has its own Van Allen belts. Even so, it doesn't prevent some of its atmosphere being blown into a torus in wake of its orbit.

The fact that Mars has no thick atmosphere due to solar wind erosion is the current scientific theory right now. I don't know how to check your calculation but 12% does seem rather a little.

[Karlos]

@Kenny

I'm not disputing the fact that it causes atmospheric erosion, I'm just guestimating the extents.

As for the erosion of venus atmosphere, the point I was making is that if the solar wind has had billions of years to reduce it, why is it still so massively dense? Its true that venus does have its own van allen belts, but the total magentosphere of venus is very weak compared to earth (hinting at some differences in internal state).

As for the calculation, like I said, its a simple inverse square calculation to estimate the solar wind flux at mars' mean distance relative to earths, and that was 0.43.

Then I just factored in the difference in area of the earth and mars. Mars surface area is 0.28 that of earth (if you divide out you get rid of the 4pi terms etc), so it can only be exposed to 0.28 x 0.43 = 0.12 the total flux we are based on it's relative size and distance from the sun.

Perhaps the reasoning is flawed, feel free to play with the figures.

[Karlos]

Still on the issue of magnetospheres, according to this geology site, Venus' magnetosphere is 1/25000 the strength of earths.

Hence it can't exactly offer much protection from the solar wind, which is even more intense there (inverse square law again) than here.

Since venus average orbital distance is 108 million km compared to earth's 150 million km, the solar wind flux at it's distance relative to here is 1.92x greater, assuming inverse square relationship again.

According to the same site, Mars' magnetosphere is 1/5000 that of earth, which makes it 5000 times stronger than venus.

So again, how come the atmosphere is still so vast after so long?

[ivier]

Myth: Chlorophyll is green
Fact: Most Chlorophyll on Earth is green, BUT alot of it is purple, and has 70% efficiency when compared to green chlorophylls. Green however is NOT neccessarily as efficent as chlorophyll can get, just the most efficient, that earth life has found. 95% of all plant species on earth use green chlorophyll, but theres still the other 4.9999999% using purple. but there are other chlorophylls as well, they are quite rare, usually found in unusual algae and moss.

To say mars has no photosythisizing life because there is no green, is the same as saying, a city has no taxis, because there are no yellow cars.