Why are scientists always assuming life on other planets need water or similar climates to ours to exist?

Question

It seems that they always assume that life has to be similar to ours to exist, but why don't they consider the fact that life could be completely different elsewhere? A form of life that lives off perhaps something that doesn't exist even on Earth? Who knows maybe there is even life on Mercury or Pluto despite the extreme temperatures? We know so little about space and considering most of the stars you can see at night are "suns" of other solar systems who knows what's out their?

Answer 1

It's not necessarily that they assume but more or less that it would be easier to find life if we have a certain set of criteria to look for. Since there are technically no theories, evidence, or anything else that would give us a set of guidelines to go by on the search.

Answer 2

They don't, not in absolute terms anyway.  However, water is a very special compound, I could write pages about it, but not here.  Suffice it to say scientists know that the presence of certain conditions will produce life likely in some form we would easily recognize as life, one of these conditions is presence of liquid water, the universal solvent, even if it was in the past.  Until we find something else that re defines how life can begin, we will always look for water first.

Answer 3

I think they are also looking for a planet that we could go to if we ever need to. Or are looking for life that is as close as possible to us.

Answer 4

They don't assume that anymore.

There are groups of scientists that are investigating and experimenting with alternative environments for life.

But to find life, we have to start with what we already know.

Life on Earth needs water (and to some degree oxygen, though that's not as critical to all life).

Water is made up of hydrogen (the most abundant element in the universe) and oxygen (the 4th most abundant element in the universe).  Water molecules have been found in nebulas, in comets, and likely in asteroids as well (not to mention Mars).  So water is likely a common compound everywhere.

Answer 5

Because h20 is the most common thing that is liquid at room temprature.  A liquid environment is needed for molecules to move around and interact with each other.

Answer 6

Because 100% of every kind of life we know about needs water to exist - or at least, to start out.

Other elements/molecules just aren't as good at both bonding to and breaking down stuff as water is.  Water is efficient for all the life proccesses we can conceive of.

Even the extremophiles on Earth started OUT in watery conditions, and adapted to life inside rock or ice later.

What you're saying is certainly at least theoretically possible.  But it seems unlikely from what we do know.  Even so, we know how to look for "life as we know it."  Since we don;t know what form "life as we don't know it" would take, it's nearly impossible to look for it on anything but the extremely macroscopic scale (so, if we found obvious roads and cities and moving "things" on a planet like Venus, we'd have to reconsider) so until that happens it just makes more sense to look for what we can identify.

Answer 7

Always?  no.

There are scientists who have looked at other types of life, using solvents different than water.

However, there are two things that favor life based on water, for intelligence.

1.  The solvent must have certain properties such as an acceptable level of polarity and weak bonds, a wide range of temperatures where it is liquid (all the previous properties lead to a strong surface tension);  as a bonus, water offers that its frozen state is less dense.  This means that ice stays on top, acting as insulation for the rest of the water body (life can go on in the depth).  

If ice sank to the bottom, then the top liquid layer would be exposed and freeze.  In winter, all rivers and lakes would freeze and aquatic animal life would die.

2.  Speed of chemical reaction are faster at higher temperatures.  Chemical reactions double in speed for each 20 C increase in temperature.  On Titan, there seems to be a sufficient abundance of carbon-based molecules, with oxygen nitrogen, etc., and stable bodies of liquid (ethane and methane).  However, the surface temperature of -180 C would mean that chemical reactions are going on at (roughly) 1/1000 th the rate of chemical reactions at +20 C.

It would bring new meaning to the phrase "slow-witted".

There are other solvents that are considered for life, but they all have a lot more inconveniences that a water-based life does not have.

Answer 8

bcuz you have to start somewhere.

we know, in some detail, how water-based life behaves. we know what to look for, and we will know it when we see it.

when we send space probes to other planets we have to be very specific in what we put on them, and what it does. again, looking for water-based life is a reasonable place to start.

Answer 9

We don't - life could be silicone based, all kinds of possibilities

Answer 10

You're right. They assume too much, all based on the laws of nature they have around them to go by. But who knows what may be possible, with all the combinations of ingredients in the universe, anything is possible.

Answer 11

Because it's a good place to start. Once we find life on other planets living in circumstances similar to ours, we will have a basis to start looking for life forms that are more diverse.

It all takes time, and since we have yet to discover life outside of our own planet it's best to start simple and work toward the complex, rather than the other way around.

Answer 12

There are over 9 billion people on this planet. Our resources won't last forever. One day we're going to have to go out into the stars and find another planet.

Answer 13

We won't be able to actually land on any of these planets at any time in the foreseeable future.  At the moment, the only kind of life we know how to recognize is our kind of life, which needs water.  So that's why we're looking for water.

Answer 14

just that all life as we know it needs water to survive.  There are many other possibilities for life to exist, such as being Silicone based rather then Carbon, however they look for water because that is the only proof we have so far.