# Life on mars

1. Dec 7, 2004

### primal schemer

Hi Guys,

Just a question that has been bugging me for a while about looking for life on mars (or any other planets).

When landing on mars, NASA (or whoever) always seem to search for water as a sign that life once existed on mars. Is it not a bit presumptious to think that just because life on earth requires water, that life on different planets will too??
Is it that unconceivable to think that there could be a life form that can live off different 'food' (minerals from rocks, sunlight, for example)???

I know that the biology of everything we know (obviously) comes from the life forms on this planet, but isnt that a fairly small sample to be using??

Cheers,

PS

2. Dec 7, 2004

### Nereid

Staff Emeritus
This is, of course, a problem when it comes to searching for 'life'.

There are many fine-sounding reasons why 'life' needs water, and it's quite a challenge to point to some carbon-based chemistry in which complex systems of complex molecules can do their things without water.

However, not all searches for extra-terrestrial life are searches for water. For example, even on Mars, one of the main instruments used to look for life is the humble camera ... if you can see something moving, and it's not a shadow, being blown by the wind (etc), then it could well be life! In other searches, there is no immediate assumption of the need for water ... one way you could infer life on Earth is the presence of gases that are not in (long term) equilibrium, so analyses of the atmospheres of other planets could suggest life is their compositions were 'unbalanced.'

Finally (for now), consider the famousSeti@Home - the only assumption about 'life' being made by this search is that ET can transmit powerful radio signals!

3. Dec 7, 2004

### jcsd

If you saw that program on the telly "What we don't know" (or something like that) with Martin Rees, they pretty much answred that question. Organic molecules are known to exist in outer space and we alreday know that they blueprint of carbon-based life with water as a solvent works.

4. Dec 7, 2004

### Chronos

It makes sense to look for the kind of life forms we do know exist and they all require water.

5. Dec 8, 2004

### Phobos

Staff Emeritus
Welcome to Physics Forums, primal schemer!

6. Dec 8, 2004

### turbo

It is certainly not inconceivable. I prefer a very loose definition of life: I would define as "life" any organized self-sustaining and (preferably) self-reproducing construct that can exploit energy differentials for its own benefit. Could there be creatures living in space, creatures living in the atmospheres of gas giants, creatures living on the surfaces of planets with no water? If not, why not?

We may find that life is both pernicious and tenacious, and I suspect that statistically, any environment that lasts long enough and is not subject to radical swings in condition may eventually give rise to "life" of some kind.

7. Dec 8, 2004

### Nereid

Staff Emeritus
How would you - primal schemer and turbo-1 particularly - go about searching for life (other than the methods already being considered - and implemented - by NASA)?

8. Dec 9, 2004

### primal schemer

Thanks!! You guys are friendly, thats about the 4th welcome Ive got!!!

Good question. I realise that, of course, only having one sample life type (if you can group all life on earth into a 'life type') means that it's the only one we can base a search on, but

1) Even if we do find water on another planet, it is no guarantee that there will be life (seeing as we have an abundance of water and life only started here once!!)
2) If we dont find water on another planet, it is no guarantee that there cannot be life there.

As to how I would go looking, well I hadnt thought that far ahead really!! But I guess I would try and cast as wide a net as possible (which I am sure NASA are doing). Although looking for life on other planets kinda reminds me of a blindfolded man trying to find his way around a room!!

9. Dec 9, 2004

### Nereid

Staff Emeritus
and some of us are gals too!
yes you can ... with the possible exception of some viruses (which may not be 'life'), all earthly life shares an astonishingly broad range of things
I think you mean liquid water ... H20 exists in vast quantities throughout the universe, but almost entirely as either gas or solid. Also, it's not at all certain that life 'started' here (maybe life was seeded, via interplantary meteors, or even interstellar dust grains :surprised ); also, we probably have no way of ever knowing how many times life began on Earth, only the wiped out by the next planetismal impact (which melted the 'crust' to a depth of, say, 10 km).
Indeed. However, you then have the problem of determining whether there is, in fact, life there!
Fascinating, isn't it! If you've read some of the good science fiction, you'll have seen that some writers have put a lot of serious effort into thinking about what 'life' based on entirely different systems might be ... one of my favourites is (Benson?) mid-density plasmas; a second favourite is 'lifeforms' on the surface of neutron stars (or was it white dwarfs?). The one I've not seen any writer even try to imagine is 'life' made of (non-baryonic) dark matter. :tongue2:

10. Dec 9, 2004

### Andromeda321

I always thought water was sought so much based on what we've seen on Earth: it is incredibly diverse to the point where it boggles the mind but virtually all of it needs some form of water to survive. The opposite is true: where you have water you are pretty guaranteed to find life. This is an incredibly universal thing on our little planet so as a result it seems like a good place to start when searching for life elsewhere.

11. Dec 9, 2004

### turbo

I have no idea. Someone from outside out solar system should be able to find us pretty easily if they had developed microwave/radio communications, for instance, but what if the most highly developed form of life on Earth was a whale? Whales communicate through acoustic signals, which they developed (presumably) because such signals are efficiently transmitted through water. None of us here (I hope!) would deny that whales are highly developed, very intelligent life-forms. Nevertheless, they would be undetectable from Mars or even the Moon. Detectability should not be considered a factor in the definition of life, nor should it be a factor in the definition of intelligent life. There may be intelligent life near us (in the cosmological sense) that has left NO traces that are discernable to us.

Last edited: Dec 9, 2004
12. Dec 10, 2004

### Chronos

The same may be said of human life forms. Radio signals may be so primitive and range limited that no 'intelligent' civilization could ever hope to detect them.