Life On Other Planets

[CoolVikingCo]

Just a quick question: How do we know what life on other planets (if there is) would need? For example, life on Earth needs oxygen, water, etc. But what about life on other planets? Is it possible that they use methane instead of oxygen?

Sorry if you didn't understand my question

[Bill Phil]

Life would likely have a lot of Carbon, Hydrogen, Nitrogen, and Oxygen in it. Not to mention a little bit of sulfur and phosphorous. The biggest difference would be the cycle, perhaps red photosynthesis will be more dominant?

Likely using water as a solvent...

The biggest difference would be the shapes of the animals and their anatomy.

[technicalfool]

It's possible for some life on Earth to get energy without oxygen.

Aerobic respiration is what you're familiar with, however there are organisms that work through anaerobic processes that don't involve oxygen, and some that can switch between different methods of producing ATP or whatever chemical is being used as a cellular energy source.

Methane has been proposed theoretically as a chemical that could be involved in some kind of life form, but the only way we're really going to find out is to send probes or go there!

[Sirrobert]

Actually life on earth started without any oxygen. The sudden influx of oxygen caused a mass extinction. Oxygen is actually pritty toxic stuf.

More generally, methane is an example of an organic molecule, which can only be formed by life (or geological activity), and is (relatively) quickly decomposed in an atmosphere. So the exitance of such organic molecules would be a strong hint towards life

[lajoswinkler]

Life doesn't require oxygen. Even today, large part of the total living biomass is anaerobic. It's part of the biosphere that survived the oxygen disaster and managed to stay undercover, away from that poisonous gas.

Methane we see on places like Titan is primordial. It's condensed nebula we were made from.

Because of their high abundance and extreme stability and versatility of carbon, oxygen, hydrogen, nitrogen, phosphorus and sulfur compounds, you can bet all life begins with those in aqueous solutions.

Shapes of organisms depend on what they do and where they do it and you can bet on high similarities to our invertebrates, if they get to complex multicellular levels.

[CoolVikingCo]

OK thanks guys! Just started Biology, so sorry if this question seemed a bit dumb to you .

[musicpenguin]

Just a continued question. How do we know that some other life somewhere in space needs anything that we need? Something we might think that isn't alive might be alive but due to our standards we dont consider it alive. For example viruses(?) aren't really considered alive.

[magnemoe]

Life doesn't require oxygen. Even today, large part of the total living biomass is anaerobic. It's part of the biosphere that survived the oxygen disaster and managed to stay undercover, away from that poisonous gas.

Methane we see on places like Titan is primordial. It's condensed nebula we were made from.

Because of their high abundance and extreme stability and versatility of carbon, oxygen, hydrogen, nitrogen, phosphorus and sulfur compounds, you can bet all life begins with those in aqueous solutions.

Shapes of organisms depend on what they do and where they do it and you can bet on high similarities to our invertebrates, if they get to complex multicellular levels.

However oxygen is pretty much required for advanced life. anaerobic reactions provides far less energy so you will hardly find large creatures and at least not something fast or smart.

Agree on shapes, fun thing is how fish, sharks, wales and dinosaurs who lived in water looked so much alike.

It depend a lot on conditions, animals in water has to be streamlined, large animals has weight and structural constrains, yes you could get six limed creatures if the first fishes who entered land had six fins.

[Bill Phil]

Life doesn't require oxygen. Even today, large part of the total living biomass is anaerobic. It's part of the biosphere that survived the oxygen disaster and managed to stay undercover, away from that poisonous gas.

Methane we see on places like Titan is primordial. It's condensed nebula we were made from.

Because of their high abundance and extreme stability and versatility of carbon, oxygen, hydrogen, nitrogen, phosphorus and sulfur compounds, you can bet all life begins with those in aqueous solutions.

Shapes of organisms depend on what they do and where they do it and you can bet on high similarities to our invertebrates, if they get to complex multicellular levels.

Oxygen is in sugar, which forms the backbone of DNA and RNA, and is present in amino acids which are extremely important to life.

Breathing oxygen is not the same as using it. Oxygen is quite important in the overall cycle.

Edited February 1, 2015 by Bill Phil

[NFUN]

Carbon, which almost certainly will be integral to nearly all life, makes some pretty interesting bonds with hydrogen and oxygen. Since these elements are known to be common in the Universe, they are also going to make up much of life.

[Stargate525]

There are some biologists which have discovered bacteria living in some lakebeds which breathe metal, and another which can survive on the head of an electrode without any additional energy input.

So... Go there and see if something moves?

[Newt]

Go there and see if something moves?

I like that.

Really, we can make a lot of guesses about life, but, at present we have a tiny understanding of life. You cannot really understand the politics, culture and history of a country by looking, however deeply, at a village, and we probably cannot understand the diversity of life by looking at a planet. We did not expect, really even conceive of a hot Jupiter, until we saw one. we did not expect gysers on Triton. When we first came to Mars, we were surprised by the great number of craters, ad when we came back, we were surprised by the duststorm, the volcanoes, the huge canyon system, we keep finding new things, and that is the essence of exploration.

Life needs some resources, molecules and energy. Very likely a solvent, and some decently versatile atoms like carbon. But not necessarily carbon, and not by definition water, or methane, or helium. We can best understand what life is by finding it, and what we need now, is probably at best a working definition, something that can meet the needs of our current society, but acknowledge that those will change in the future. Because currently, we can only see one town in a potentially very large state, and it is foolish to suppose we understand the full complexity and diversity of life in the universe from looking at the example of one planet.

[Bill Phil]

Intelligent life, or at least civilization, requires that the life form have an effective mechanism for changing the environment, or basically hands. That's why primates have built a civilization here, we have hands for grabbing branches when moving around in trees. And we kept those hands. A life form will not just evolve into a state with the ability to make tools, or it's at least very unlikely.

And it's more like comparing one person in a city to the world...

[Scotius]

http://www.sciencedaily.com/releases/2001/09/010928070246.htm

Glass eating bacteria.

Let me repeat it: living organisms that eat volcanic glass\obsidian. Gain sustenance from it. If life can find a way to eat glass and thrive on it, then it will find its way everywhere else.

[Sirrobert]

Just a continued question. How do we know that some other life somewhere in space needs anything that we need? Something we might think that isn't alive might be alive but due to our standards we dont consider it alive. For example viruses(?) aren't really considered alive.

We don't. Everything is we know is is theories and asumptions based on what we currently know.

Currently, we have a set of critiria that a thing needs to fulfill in order to be concidered alive. I can't find the exact list at the moment, but the ones I remember are:

Interaction with the enviroment, reproduction.

Viruses can't reproduce on their own. They need a host to do it for them. That's the reason they are not concidered alive.

This definition seems to encapsulate all super strange new life forms we find, and if we find something that common sense would call alive, but doesn't fit in the definition, we might have to change the definition.

[lajoswinkler]

Just a continued question. How do we know that some other life somewhere in space needs anything that we need? Something we might think that isn't alive might be alive but due to our standards we dont consider it alive. For example viruses(?) aren't really considered alive.

A sufficiently advanced computer program (AI) would be considered alive, but we're talking about biological organisms. Such life has a set of rules governing its definition. For example it must have a metabolism which it uses for gaining energy from the environment by absorbing matter and energy, it must have a membrane and an interior different from the environment (that's a hardcore rule you can not avoid), it needs to react to input (whatever the input is) by trying to nullify its effects in order not to change its basic structure. Additionally, it should be able to reproduce. That is one of the weaker rules because such ability might be lost.

Viruses are in the gray zone. They sometimes display some features of life. There are even simpler phenomena like viroids and prions. They are basically smart molecules. We might even consider them sort of a molecular error which got its ability to be expressed outside pure nucleotide code, using a foreign cell.

Even biological life is not something you can say it "is" or it "isn't". There is the gray zone.

However oxygen is pretty much required for advanced life. anaerobic reactions provides far less energy so you will hardly find large creatures and at least not something fast or smart.

Agree on shapes, fun thing is how fish, sharks, wales and dinosaurs who lived in water looked so much alike.

It depend a lot on conditions, animals in water has to be streamlined, large animals has weight and structural constrains, yes you could get six limed creatures if the first fishes who entered land had six fins.

True, anaerobic metabolism we know gives only a handful of ATP molecules.

And sedentary ones who prey will have radial symmetry with tentacles. Filtrators don't need symmetry at all.

Oxygen is in sugar, which forms the backbone of DNA and RNA, and is present in amino acids which are extremely important to life.

Breathing oxygen is not the same as using it. Oxygen is quite important in the overall cycle.

I thought it was obvious we were talking about breathing elemental oxygen.

There are some biologists which have discovered bacteria living in some lakebeds which breathe metal, and another which can survive on the head of an electrode without any additional energy input.

So... Go there and see if something moves?

They don't breathe metal, as metals are solids and also you almost never encounter metals in their elemental forms in nature, except when they're so inert they stay like that forever (gold). They get energy from reacting metal ions with something else.

You have them in your home. Iron bacteria. They get energy from oxidizing Fe²⁺ into Fe³⁺, and get the matter from traces of organic molecules in the water.

It's the gooey rust you probably encountered before.

http://www.sciencedaily.com/releases/2001/09/010928070246.htm

Glass eating bacteria.

Let me repeat it: living organisms that eat volcanic glass\obsidian. Gain sustenance from it. If life can find a way to eat glass and thrive on it, then it will find its way everywhere else.

It might not even be their sustenance, but only a source of energy. Then again, they probably incorporate some of the liberated ions into their cells.

Edited February 1, 2015 by lajoswinkler

[magnemoe]

A sufficiently advanced computer program (AI) would be considered alive, but we're talking about biological organisms. Such life has a set of rules governing its definition. For example it must have a metabolism which it uses for gaining energy from the environment by absorbing matter and energy, it must have a membrane and an interior different from the environment (that's a hardcore rule you can not avoid), it needs to react to input (whatever the input is) by trying to nullify its effects in order not to change its basic structure. Additionally, it should be able to reproduce. That is one of the weaker rules because such ability might be lost.

Viruses are in the gray zone. They sometimes display some features of life. There are even simpler phenomena like viroids and prions. They are basically smart molecules. We might even consider them sort of a molecular error which got its ability to be expressed outside pure nucleotide code, using a foreign cell.

Even biological life is not something you can say it "is" or it "isn't". There is the gray zone.

True, the problem with viruses is that they are not alive an way without cells to infest, not so simple as saying an predator will starve to death without prey too as its alive but has not that it need to survive. The virus does not have metabolism. Prions are far less alive its an molecule who is able to make copies of itself in the right solution, no inside or outside, just a decent complex organic molecule.

True, anaerobic metabolism we know gives only a handful of ATP molecules.

And sedentary ones who prey will have radial symmetry with tentacles. Filtrators don't need symmetry at all.

Yes however this is a bit below that I call advanced life as in after cambium, yes octopus are are also advanced life and pretty smart however they have a two plane symmetry.

- - - Updated - - -

Intelligent life, or at least civilization, requires that the life form have an effective mechanism for changing the environment, or basically hands. That's why primates have built a civilization here, we have hands for grabbing branches when moving around in trees. And we kept those hands. A life form will not just evolve into a state with the ability to make tools, or it's at least very unlikely.

And it's more like comparing one person in a city to the world...

True, trunks or tentacles might work but has downsides. An six limb body plan might be beneficial here as you have the front limbs pretty free without having to walk on two legs, however the dinosaurs managed that part a long time ago, however none of them had useful hands.

[Bill Phil]

Life doesn't require any oxygen.

Not obviously talking about breathing it if you ask me.

[GoSlash27]

The short version is we don't.

Life is essentially a chemical process, and can exist in all sorts of weird circumstances.

The thing is, if it's sufficiently chemically different we may not be able to recognize it as "life"

Therefore we seek circumstances we are familiar with so we'll recognize life when we see it.

Best,

-Slashy

[Sirrobert]

True, the problem with viruses is that they are not alive an way without cells to infest, not so simple as saying an predator will starve to death without prey too as its alive but has not that it need to survive. The virus does not have metabolism. Prions are far less alive its an molecule who is able to make copies of itself in the right solution, no inside or outside, just a decent complex organic molecule.

Didn't life basicly start as complex organic molecules that were able to copy themselves?

[KerikBalm]

True, anaerobic metabolism we know gives only a handful of ATP molecules.

Well, glycolysis does, there are other anerobic metabolisms that are nearly as energetic.

For example, sulfate reducing bacteria. In this case S basically substitutes for O... which makes sense... same column of the periodic table and all.

But there are many limitations that make it unlikely there would ever be a world where this dominates over Oxygen (Oxygen dissolves much more readily, is a gas, is more common in the universe, is more electonegative, etc)

http://en.wikipedia.org/wiki/Sulfate-reducing_bacteria

But there are other terminal acceptors of electrons from the respiratory chain... some of which are metals... which means the following is false:

They don't breathe metal, as metals are solids and also you almost never encounter metals in their elemental forms in nature, except when they're so inert they stay like that forever (gold). They get energy from reacting metal ions with something else.

You have them in your home. Iron bacteria. They get energy from oxidizing Fe²⁺ into Fe³⁺, and get the matter from traces of organic molecules in the water.

There are bacteria that reduce metals.

http://en.wikipedia.org/wiki/Shewanella_oneidensis

http://en.wikipedia.org/wiki/Geothrix_fermentans

https://microbewiki.kenyon.edu/index.php/Dissimilatory_metal_reduction

Reactions like:

acetate- + 8 Fe(llI) + 4 H2O → 2 HCO3 + 8 Fe(lI) + 9 H+

or

formate- + 2 Fe(III) + H20 → HCO3 + 2 Fe(II) + 2 H+;

lactate - + 4 Fe(llI) + 2 H2O → acetate - + HCO3 + 4 Fe(II) + 5 H+;

pyruvate - + 2 Fe(lII) + 2 H2O → acetate - + HCO3 + 2 Fe(II) + 3 H+.

As to those that think these bacteria mean life can be anywhere... uuuhhh... no

They are carbon based

with water as a solvent

they make use of a chemical energy gradient.

None of this changes what we'd look for in a habitable planet.

For a long time (since the 70's), we've known that the energy sources that can be used are highly divergent.

One simply needs:

1) an energy gradient, and life will likely have find a way to use it (well... to an extent, we've got no evidence of life mediating nuclear reactions... it seems limited to chemical reactions).

2) Carbon (as the main constutient of the biological molecules). Its got to be carbon based... don't give me that silicon based life spiel.... the varieties of abiotic naturally forming carbon molocules are astounding. In contrast, Silicon molocules are rather monotonous and only a handful of varieties are found. No other element has the flexibility. Even if Boron did - Boron is cosmically rare

3) A solvent for the various chemical reactions to take place in.

Water is the best candidate... but I'm not entirely put off the idea of ammonia, ammonia/water mixtures, or even a non polar solvent (in which case, the arangement of hydrophobic/hydrophllic groups would be reversed, and complex lipid may substitute for proteins).

1) is easy, its available on Titan and Europa (we know there is a chemical energy gradient on Titan, and assume one is there on Europa due to tidal heating)

Direct sunlight (ie, the surface of a planet) also drives chemical reactions - mars meets this requirement (it likely has residual geothermal as well

2) Available on titan and Europa, mars, etc... its pretty common

3) A major problem... a solvent is a liquid, and the only body with surface liquid that we know of is:

Titan... and thats not water, and its doubtful that it would work. Ter energy gradient isn't that large as well, and its really cold which would slow the reactions...

Well... there is also io, with magma reaching the surface. Magma is far too hot for something made of Carbon, the chemical bonds would breakdown, and your molecules with complex structure are gone (and any hope of life along with it).

So that leaves subsurface liquids.. Europa, Enceledus... Mars?

Subsurface means that while ou do meet requirement #1, you're missing out on a major source of energy... sunlight, and biomass and biodiversity are probably limited in comparison.