I can only say 'Hear, hear' even though I have stopped clinging at straws entirely on the matter of life on Mars. As said elsewhere im old to have lived since the days when almost every astronomical textbook described the seasonal growth of lichen on the Martian surface.
That most certainly started my life long obsssion with the planet, and its still there even after I have faced the truth that the planet are dead.
It might or might not have had life in the past, we might find the signs of that past life later, after some future lander or rover drills down a few feet into the permafrost. I would view that as icing on the cake.
Remember we are a very privileged group of people with the fantastic exploration we got here and now, one kind of exploration the writers of those textbooks from the 1960's would have given one arm and a leg to witness!

If Marsian organisms, even microscopic, evolved into the depths, they could find hot environments rich into nutrients, like on Earth with the "black smokers", hot water springs in the bottom of the oceans. So Marsian bacteria may have evolved into forms able to survive on Earth, and may be brought to surface in hot springs. Eventually, if their "DNA" or whatever plays its role, is faster to duplicate than Earth DNA, they could overcome many microbian life on Earth. It is why a mission like Mars Sample Return can be very dangerous, if appropriate cautions are not taken (for instance the box should withstand a full speed impact on Earth, withstand corrosion and self destroy itself if it is not found)

Could martian bacteria destroy all Earth life? Several more conditions are required for this. Most likely, they could create shifts into ecosystems, or new diseases. But if they can interact with our DNA in a virus-style way, every life form is at risk.

Very very unlikely. Remember that nearly all microorganisms are completely harmless. It takes very special adaptations to circumvent immune defences and actually infect another species. Martian bugs are not likely to be that closely related to us.

Virus are even more unlikely. They reproduce by injecting their DNA into a cell, incorporating themselves into the cell's DNA and using its biochemical facilities to make copies of themselves. This requires exquisite adaptation to work, and viruses (fortunately) don't often manage to jump species barriers even among us closely related terran life-forms.

Also if it could happen it would already have happened. Martian meteorites have been arriving for four billion years without self-destruct facilities. Shades of Hoyle and Wackramasinghe.

tty

that bacteria could survive a several million years space travel is only an hypothesis until now, not an established fact. It has been proposed only to explain a strange life form, the nanobacteria, which are even not recognized by all the scientists as they are much smaller that the minimum size expected for a bacteria.








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Marsian bug may be very dangerous by creating ecological unbalance. For instance if they could live into the soil, they could take the place of humus bacteria and destroy all our food resources. And if they are made of something else than our usual amino acids, they could be invisible for our immune systems and develop anywhere uncluding in our bodies, creating dangerous diseases without immune responses.




OK not viruses which are very specialized. But if a martian "something" feeds with proteins or DNA without our cell barriers are able to stop it, a bit like the prions, abnormal proteins able to pervert normal proteins and propagate like an infection, we are all dead.


Numerous scenarios are possible for Marsian life hampering or destroying Earth life, some predictable, other we can even not imagine. This is why we cannot bet that what will be in the sample return capsule does not pose a dreadfull threat for us all. Even the surface of the capsule should be thoroughly sterilized before sending it to Earth.

With my opinion the safest scenario is to send the capsule on a trajectory where the Moon places it in Earth orbit, never aiming at Earth itself. It will be more costy to recover it, but safer than to send it direct on the ground, especially in the case where recovery fails. We never know, for instance a war or a major natural catastrophe breaks up during the travel... At least with this scenario the capsule is left in space and not rusting in some desert, releasing death fifty years later.

Well, any life on Mars ia also just a hyposthesis as well. Over time as we know more and more about Mars the area where life could possibly reside has shrunk considerably. In the 1890's it was (almost) accepted wisdom that a civilization was there. In the 1950's - 60's it was "known" that plants or lichen came and went with the seasons. In the 1970's, until Viking, it was thought that life could be in the soil on the surface. Still nothing.

Now we are left with the only possibility that life is deep underground. It seems that life is always "just around the corner" on Mars but as soon as we look around it and it is not there , we just come up with even more unlikely scenarios of where it might be. I am sure once we start drilling the surface and do not find life, people will say we did not drill in the right place or deep enough and that life is really in the mantle not the crust, etc, etc.

The problem is that we can never "prove" that life does not exist on Mars (you cannot prove a negative). It seems clear that there is no life on Mars' surface and if any life exists below the surface it would have to be in very small quantities since we would have detected the gases associated with biological activity in the atmosphere by now.

Therefore we should not let contamination issues overly affect our exploration of Mars. Yes, reasonable precations should be taken like clean rooms and sterilization when needed, but to put a blanket ban on all manned landings or sample returns makes no sense and is not supported by the evidence to date.

There is no law in celestial mechanics that a martian meteorite has to spend millions of years before reaching Earth.
Just to get a handle on numbers and probabilities. I seem to remember that a total of 18 martian meteorites have been identified so far. Assuming (very optimistically) that the number of meteorites in scientific collections is equal to one average years crop of meteorites falling to Earth that sums to about 7*10^10 Martian meteorites since the late heavy bombardment!




I should think that would make the immune system react very strongly. In any case a life-form containing other amino acids than earthlife would be harmless since it couldn't possibly feed and procreate here.

tty

"Marsian bug may be very dangerous by creating ecological unbalance."


Should Mars have life at all, it would be a much less complex ecosystem. I think the real risk here is that our own microbes will destroy any such martian microbes before we can study them. I think the risk of the reverse of this happening is too insignificant to worry about.

An essential point is that there are probably essentially two types of life-bearing planets.

1) Planets with cryptic life, possibly abundant and profuse, but in a hidden, protected ecosystem. Martian life, if present, is probably restricted primarily to the probable watertable, concentrated in areas of "geo" thermal heating and active chemistry. Europa life, if present is in the probable brine layer between the ice-crust and the rock-mantle. It may have periods of flourishing during episodic tidal heatnig cycles. In both cases, life does not dominate the open surface environment and controle the chemistry and physical properties of the surface and atmosphere.

2.) Profusely life-bearing planets. Earth. See the "Gaea Hypothesis" stuff by Lovelock and Margolis <sp?> for an extreme take on the ideas.

I don't seem to see this point made in discussions of exobiology. Type 1 planets probably outnumber type 2 by hundreds to tens of thousands to one, but we can only voice prejudice on the odds so far.

Interesting idea. According to the latest biological ideas, the Earth actually is of both types! This theory claims that most of life (in mass and in numbers) can be found deep below the surface, up to 3 or 5 kilometers deep. Life on top of the surface should be regarded as 'icing on the cake'. From time to time, the icing is destroyed and for a short while the Earth is a pure type 1 planet. (Like after the impact that created the Moon or when our planet is covered with ice from pole to pole) However, it doesn't take long for those critters underground to find their way up and colonize the surface once more.

This leads to the conclusion that every living planet is actually of type 1 and only under very special conditions (liquid water on the surface) can it migrate to the surface. The question is whether Mars is a prime candidate for such underground life. I think the icy moons of Jupiter and Saturn are better candidates, as they possess lots of active vulcanism and the perfect chemistry.

The good news is of course that within 2 years we will know if there is liquid water under the surface of Mars! (With 2 ground penetrating radars in orbit that shouldn't be too much to ask...)

I think you're right, but with the caveat that the second group of planets is actually a sub-set of the first - even on Earth, the visible surface macro-ecology appears to be grossly out-performed by the bugs which live well below our feet. What we tend to describe as a 'less complex' cryptic ecology may well be a highly evolved and highly efficient system, which our prejudiced world-view fails to acknowledge.

As well-preserved life-bearing rocky material may travel quite quickly between the terrestrial planets and planetary bodies (not to mention asteroids and comets, KBOs, moons...) then I, for one, would be quite surprised *not* to find some form of life-as-we-would-know-it-if-we-could-be-bothered-to-look in most potential ecological niches. As for which came first, and the relationships between the various branches, well, that's a fascinating set of questions for once we have some samples!

The impact that created the Moon almost certainly sterilized the Earth completely. In any case it is doubtful if life had had time to develop (it probably happened 4.45 bya). The Late Heavy Bombardment c. 3.85 bya may well have sterilized the surface, but probably no incident since then, not even the extreme neoproterozoic ice ages. A number of macroscopic metazoan lineages go back before that time, and so must have survived somewhere (deep sea vents? hot springs?). As far as can be judged from the sparse data (mostly acritarchs) a lot of lineages did become extinct.

tty

Although the proto-Earth was, it appears, dealt a mighty whack, and the whole place became untenable as an abode of life, presumably much debris was ejected which then returned to the planet over a period of a few tens of millions of years - just as it would today. Much debris would have landed on a very hot and inhospitable planetary surface, but as time went on things would have improved. I suspect that while Earth may have been sterilised, any rock-dwelling life from before the big impact might have returned to the planet in due course. A good proportion of such returnees probably got hit by the next pile of junk falling onto the surface, but...

Additionally, if life did gain a foothold here before the big whack then imagine how much debris from Earth contaminated the whole inner Solar System! From what I've read, the collision which is accepted as creating the Earth/Moon system must have been just about the biggest ever in our locale, and would have generated a commensurate amount of rocky spaceships!

If by "our locale," you mean Earth or the inner Solar System, you're right. But for the Solar System in general, I bet the impact that tilted Uranus on its side was a bigger, more violent event.

-the other Doug

At number #3 in the charts there's the one that ate up (and then some) Venus' rotational energy.

Number #3?

Let's see - lifting the Moon to lunar orbit = ~4*10^30 joules
Cancelling the spin of Venus (assuming initial 24hr rotation period) = ~4*10^28 joules.

That's a lot!

Andy G

Two other big (though somewhat hypothetical) collisions:

1. The one that stripped the mantle off Mercurius

2. The one (or maybe more than one) that differentiated the northern and southern hemispheres on Marss.



And the same thing happened again on a somewhat smaller scale (and perhaps a little less violently) during the Late Heavy Bombardment, at which time lots of material must have been exchanged between all four inner planets. Also at that time it is rather more likely that life had had time to evolve somewhere. I suppose Mercurius has always been a pretty hopeless case, but who knows about Venus back then when the sun was weaker and perhaps less CO2 had outgassed....

Incidentally an awful lot of rocks from Earth must have landed on the Moon during the LHB and the Moon is quite possibly the best place to find out what happened on Earth pre-3.85 bya. It seems there is little chance that we will ever find much more than detrital zircons from pre-LHB days here on Earth.

tty

I've always thought that when/if He3 mining takes place on the Moon then in the spoil tip will be some real treasures!

ESA: Lichen survives in space (temporarily)



This is pretty interesting. I wonder if the lichen communities would survive in deep space though and for how long. What would happen if this got transported (safely) to the martian surface?

Should be a fairly easy experiment to do on the ground, at least the atmosphere and Uv portion of it. The rock/soil composition might be harder.

An enterprising young PhD should take this up, with simulated variations in the atmosphere and irradiance based on martian years, for different locations on Mars.