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Im not sure if this is the right place to ask, the right category, the righr dorum etc. Also im only 15yo so dont explain in too professionam terms please. But ive always wondered this... When people bring up searching for extraterrestial life its always about if water is present on the planet, why is this? I know we live from water and so do fish, where we originally originate from and the bacteria they originated from lived in water but i dont see this as proof. Cant evolution on a planet without water just work with chlorine for example, or an element not even present on earth and thus not known to humanity. Same applies to distance to the sun to have a temperature sweetspot, wouldnt another planet have life evolved to their temperature? I mean we have had animals for ice ages and, well, not ice ages... unless you really are able to prove me wrong here i feel lile we need another planet with this theory proven for it to be sure. Im not trying to start the next flat earth like community but im just trying to understand.

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37 minutes ago, Stormloop said:

When people bring up searching for extraterrestial life its always about if water is present on the planet, why is this? I know we live from water and so do fish, where we originally originate from and the bacteria they originated from lived in water but i dont see this as proof. Cant evolution on a planet without water just work with chlorine for example,

It's an excellent question!

I'm not sure about chlorine, but I have heard arguments for an ammonia-based lifeform. It's not assumed in science that water is required for life, just that we know how well water supports it. It's also our best chance to find life similar to ours.

You should study water. It's an interesting molecule, with some unique properties. I think it's the only substance where its solid state floats in its liquid state. 

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On ‎10‎/‎26‎/‎2020 at 5:45 PM, Phi for All said:

 I think it's the only substance where its solid state floats in its liquid state. 

I'm not sure about the floating part, but there are other substances that expand when frozen solid.
Silicon and Gallium ( used in semiconductors ) come to mind, but I'm sure there are others.
Has to do with the way molecules aggregate into the solid crystal structure taking up more space than freely moving molecules.

It is fortunate that ice floats for Earth based life, meaning seas and oceans don't freeze from the bottom up, and aquatic life is possible.
But this wouldn't be necessary on a planet where the temperature doesn't drop below 00 , or where the prevailing liquid has a wide temperature range liquid state.
We are limiting our criteria of life, to life 'as we know it'.
But there are certainly arguments for life based on other chemistries.
Carbon based life is suited to temperatures where water is liquid, but at much higher temperatures sulfur based or even silicon based life might be possible ( sulfur and silicon don't form as many compounds as carbon, but they are prolific in their bonding ).

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We have no examples of other kinds of biology. Water, as well as the elements and precursor compounds terrestrial life rely upon, appears to be widespread through the known universe and on planets. Even as hypotheticals/theoreticals, other kinds of chemistry look problematic. We may be able to model possibilities and find something that could work to produce life, but so far as I know none look promising. We may find that even with water based/carbon based life there may only be limited ways self replicating complex biochemistry can arise, ie that alternatives to our RNA/DNA/protein based life as we know it may be very unlikely or even impossible.

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  • 1 year later...

To begin with: why water is important generally on Earth: Almost all life on Earth uses a membrane that separates the body from the environment. To stay alive, the body takes on important materials to generate energy, filtering out toxic substances like waste. Due to this, water is essential because it remains liquid at earth temperatures. As it flows, it provides an efficient way of transferring substances from the cell to the cell's environment. It is much more difficult to release energy from a solid (although there are microbes that eat a stone.

In addition to the fact that water can carry substances into and out of the cell, it is associated with a unique chemical configuration. The humble water molecule is made up of two hydrogen atoms bonded to an oxygen atom. Water's amazing dissolving properties make it ideal for transferring substances like phosphates or calcium ions into and out of the cell. 

Moreover, water can be more than a liquid that makes life easier - it can be the protective cradle that brought the building blocks of life to Earth. According to one of the theories of the origin of life on Earth, the theory of panspermia, ice comets crashed into the Earth, carrying tiny organic molecules that became the basis for life. But traveling through space is an ordeal, primarily because of the powerful levels of radiation that can destroy delicate organic molecules. However, water in its solid form can protect molecules from radiation.

Despite the fact that water is important for life on Earth there may be life forms that do not live by the rules of earthlings. Among the main contenders are ammonia and methane. Ammonia, like water, is a polar molecule relatively common in the universe, but scientists have not yet found large bodies with ammonia in the solar system. Ammonia, like water, is a polar molecule relatively common in the universe, but scientists have not yet found large bodies with ammonia in the solar system. Methane is not polar, but it can dissolve many other substances. However, unlike water, methane becomes liquid only at very cold temperatures - at minus 182 degrees Celsius.
We know that Titan has large lakes of liquid methane and ethane. Thus, a very interesting question is whether life can use liquid methane or ethane.

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On 10/26/2020 at 5:04 PM, Stormloop said:

When people bring up searching for extraterrestial life its always about if water is present on the planet, why is this?

Because of what we know about life and how life evolves and what sustaining life requires. While, in theory, there may be life forms based on other chemicals than carbon, hydrogen and oxygen, it's less likely that we would encounter such a life-form: it seems more efficient use of resources to look for conditions that we know how they work than conditions that we think might possibly work somehow. And since we have never seen an alternative system in operation, we might not recognize such a life-form if we did encounter it, which would be an even bigger waste of resources. 

 

Kind of like a detective, searching a mansion and its grounds : "I'm looking for a blunt instrument that matches this wound." vs "I'm looking for anything that connects the owner to the crime." Of course, you're always doing the second,incidentally,  but the first focuses your search on a specific outcome.  

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Considering how hard it is to get life started WITH liquid water available, I think it's probably unlikely that another kind is out there. 

Having said that, I wouldn't say that lack of water signals necessarily means lack of life. If you look at Earth, we are probably no more than a couple of hundred years from being able to inhabit space, as in large space stations, colonies on the Moon and Mars, etc. etc. So there will be life out there, that can exist without the signs of water that we are looking for elsewhere. 

And in a few hundred years, there might be artificial intelligence here on Earth, able to reproduce new units in  a way that blurs the distinction between machinery and life. So if that could happen here in a few hundred years, what might be out there? There could be civilizations out there millions of year in advance of us, with robots producing new robots, evolving new designs, all without any need for water based life. In fact, if you look at the arithmatic, it's highly likely. 

It might need water based life like us to start it off, but once you reach the stage that we are at now, the brakes could come off. 

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There seems to be some interesting chemistry happing in Titan, liquid methane and ethane lakes and seas, with a mysterious loss of hydrogen. 

 

https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#Other_solvents_or_cosolvents

 

Quote

Methane and other hydrocarbons[edit]

Methane (CH4) is a simple hydrocarbon: that is, a compound of two of the most common elements in the cosmos: hydrogen and carbon. It has a cosmic abundance comparable with ammonia.[47] Hydrocarbons could act as a solvent over a wide range of temperatures, but would lack polarity. Isaac Asimov, the biochemist and science fiction writer, suggested in 1981 that poly-lipids could form a substitute for proteins in a non-polar solvent such as methane.[47] Lakes composed of a mixture of hydrocarbons, including methane and ethane, have been detected on the surface of Titan by the Cassini spacecraft.

There is debate about the effectiveness of methane and other hydrocarbons as a solvent for life compared to water or ammonia.[53][54][55] Water is a stronger solvent than the hydrocarbons, enabling easier transport of substances in a cell.[56] However, water is also more chemically reactive and can break down large organic molecules through hydrolysis.[53] A life-form whose solvent was a hydrocarbon would not face the threat of its biomolecules being destroyed in this way.[53] Also, the water molecule's tendency to form strong hydrogen bonds can interfere with internal hydrogen bonding in complex organic molecules.[46] Life with a hydrocarbon solvent could make more use of hydrogen bonds within its biomolecules.[53] Moreover, the strength of hydrogen bonds within biomolecules would be appropriate to a low-temperature biochemistry.[53]

Astrobiologist Chris McKay has argued, on thermodynamic grounds, that if life does exist on Titan's surface, using hydrocarbons as a solvent, it is likely also to use the more complex hydrocarbons as an energy source by reacting them with hydrogen, reducing ethane and acetylene to methane.[57] Possible evidence for this form of life on Titan was identified in 2010 by Darrell Strobel of Johns Hopkins University; a greater abundance of molecular hydrogen in the upper atmospheric layers of Titan compared to the lower layers, arguing for a downward diffusion at a rate of roughly 1025 molecules per second and disappearance of hydrogen near Titan's surface. As Strobel noted, his findings were in line with the effects Chris McKay had predicted if methanogenic life-forms were present.[56][57][58] The same year, another study showed low levels of acetylene on Titan's surface, which were interpreted by Chris McKay as consistent with the hypothesis of organisms reducing acetylene to methane.[56] While restating the biological hypothesis, McKay cautioned that other explanations for the hydrogen and acetylene findings are to be considered more likely: the possibilities of yet unidentified physical or chemical processes (e.g. a non-living surface catalyst enabling acetylene to react with hydrogen), or flaws in the current models of material flow.[59] He noted that even a non-biological catalyst effective at 95 K would in itself be a startling discovery.[59]

Azotosome[edit]

A hypothetical cell membrane termed an azotosome, capable of functioning in liquid methane in Titan conditions was computer-modeled in an article published in February 2015. Composed of acrylonitrile, a small molecule containing carbon, hydrogen, and nitrogen, it is predicted to have stability and flexibility in liquid methane comparable to that of a phospholipid bilayer (the type of cell membrane possessed by all life on Earth) in liquid water.[60][61] An analysis of data obtained using the Atacama Large Millimeter / submillimeter Array (ALMA), completed in 2017, confirmed substantial amounts of acrylonitrile in Titan's atmosphere.[62][63]

 

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There is no unique definition of life in astrobiology, metabolism is one of the most mentioned features. Still biocentrism manifests life in any diversity, so there are many possible definitions.

 

Any feature of an exoplanet that doesn’t fit statistical data that we have could be a sign of life there. Unfortunately, we still do not have that much statistical data. Often the ‘misfits’ that are already found in the universe are forgotten (for instance, wandering planets).

 

Today there is a lot of activity directed to the exoplanets investigation, habitable zone definitions, even volunteers are called to help AI to search for exoplanets.

James Webb Telescope - the great mission is also targeted for exoplanets observation.

 

Major defining criteria for a candidate of potential life holder are :

- exomoons stable systems;

- water containing planets;

- exomoons near to gas giants;

- any ‘Earth-like’ planet or exomoon might be a candidate for an alien life.

 

'To date, more than 4,000 exoplanets have been discovered and are considered "confirmed." However, there are thousands of other "candidate" exoplanet detections that require further observations in order to say for sure whether or not the exoplanet is real.' - NASA

https://exoplanets.nasa.gov/faq/6/how-many-exoplanets-are-there/#:~:text=To date%2C more than 4%2C000,not the exoplanet is real

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On 12/3/2021 at 12:36 PM, mistermack said:

Considering how hard it is to get life started WITH liquid water available, I think it's probably unlikely that another kind is out there. 

How hard is it?

We have one data point for life getting started on a planet with liquid water, and there is life. How does one extrapolate that to get a level of difficulty?

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41 minutes ago, swansont said:

How hard is it?

We have one data point for life getting started on a planet with liquid water, and there is life. How does one extrapolate that to get a level of difficulty?

It's too hard to do in the lab, with highly trained scientists doing their very best. You would certainly get a Nobel Prize if you could create life from non-life building blocks. 

Having said that, it's true that we only have one example to study, and that suitable planet did produce life. Or did it? It is feasible that life got seeded here from somewhere else. 

I think it's feasible, but less likely. If I had to bet the house I would say that life originated here. It is obviously hard to do in the lab, but out in the primordial world, there were billions of billions of labs, ie, unimaginable numbers of environments with slightly differing constituents and temperatures etc, and at least one managed to produce a self-replicating compound. 

I have my doubts that the same thing could happen without liquid water at room temperature, but you would need to be a real specialist to give an informed guess on that.

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It is a pity that stormloop hasn't participated further in this discussion as it has raised some interesting answers, albeit rather spread out.

I hope he or she is OK.

 

On 10/26/2020 at 9:04 PM, Stormloop said:

Im not sure if this is the right place to ask, the right category, the righr dorum etc. Also im only 15yo so dont explain in too professionam terms please. But ive always wondered this... When people bring up searching for extraterrestial life its always about if water is present on the planet, why is this? I know we live from water and so do fish, where we originally originate from and the bacteria they originated from lived in water but i dont see this as proof. Cant evolution on a planet without water just work with chlorine for example, or an element not even present on earth and thus not known to humanity. Same applies to distance to the sun to have a temperature sweetspot, wouldnt another planet have life evolved to their temperature? I mean we have had animals for ice ages and, well, not ice ages... unless you really are able to prove me wrong here i feel lile we need another planet with this theory proven for it to be sure. Im not trying to start the next flat earth like community but im just trying to understand.

 

I am currently watching a French scifi series on BBC iPlayer called Missions.

Missions is about the first few manned missions to Mars but underlying the day to day adventures one of the themes could belong in this thread.

A latter day Bezos or Musk have come to the conclusion that the only life possible outside Eath would be an artificial intelligence.

The consequences of this are worked out in the two series.

The series is also interesting as it was made at/with the cooperation of the Museum of the Moving Image which I have mentioned before and which is worth a visit in its own right.

Edited by studiot
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50 minutes ago, mistermack said:

It's too hard to do in the lab, with highly trained scientists doing their very best.

Same is true of sustained nuclear fusion, but that's happening all over the place

 

Quote

that suitable planet did produce life. Or did it? It is feasible that life got seeded here from somewhere else. 

The feasibility is debatable and that just kicks the can down the road about life starting.

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18 minutes ago, swansont said:
Quote

that suitable planet did produce life. Or did it? It is feasible that life got seeded here from somewhere else. 

The feasibility is debatable and that just kicks the can down the road about life starting.

The French production I mentioned has an interesting take on this aspect.

Edited by studiot
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8 minutes ago, swansont said:

Same is true of sustained nuclear fusion

Not true actually. The first fusion in the lab was achieved in 1932. 

It can now be sustained for far longer now. It's down to economics now.

Self sustaining I agree can't be done yet, but it's only a matter of time.

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31 minutes ago, mistermack said:

Not true actually. The first fusion in the lab was achieved in 1932. 

It can now be sustained for far longer now. It's down to economics now.

Self sustaining I agree can't be done yet, but it's only a matter of time.

That's why I specified sustained. But similarly, scientists have successfully done steps that would be involved in creating life. It's just a matter of time.

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1 hour ago, studiot said:

 

(...)

Missions is about the first few manned missions to Mars but underlying the day to day adventures one of the themes could belong in this thread.

A latter day Bezos or Musk have come to the conclusion that the only life possible outside Earth would be an artificial intelligence.

 

That conclusion seems paradoxical.  

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Sorry, that was confusing on my part.   I meant the conclusion drawn by the "latter day Bezos or Musk" in your quote seemed paradoxical. 

"...the only life possible outside Earth would be an artificial intelligence."

If they mean that humans can only survive off-Earth by uploading into more durable AI form, that is certainly one speculation.  But I was perhaps taking you too literally, and interpreting it as extraterrestrial life only being AI.  Which would beg the obvious question. 

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28 minutes ago, TheVat said:

Sorry, that was confusing on my part.   I meant the conclusion drawn by the "latter day Bezos or Musk" in your quote seemed paradoxical. 

"...the only life possible outside Earth would be an artificial intelligence."

If they mean that humans can only survive off-Earth by uploading into more durable AI form, that is certainly one speculation.  But I was perhaps taking you too literally, and interpreting it as extraterrestrial life only being AI.  Which would beg the obvious question. 

I can't remember whether it was epside 8, 9 or 10 where they stated exactly this in so many words.

"...the only life possible outside Earth would be an artificial intelligence."

 

I am trying not to spoil the series for those who might wish to watch as it was really quite good and explored many issues in a way that only SF can.
Some ideas were drawn from 'A space oddesy' - but were , in my opinion, much better done. I think oddesy was much overrated.

 

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  • 3 weeks later...
13 hours ago, NinjaFeels said:

You guys have to checkout late Dr. John Mack. Former Harvard Professor.

 

 

 

You're listening to the wrong guy in this; a myth is self perpetuating because we reinforce the mythical with anecdotes, rather than reason or evidence...

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  • 4 weeks later...
On 12/9/2021 at 12:24 PM, swansont said:

We have one data point for life getting started on a planet with liquid water, and there is life. How does one extrapolate that to get a level of difficulty?

Indeed, until we get a second data point, we are limited to informed speculation. I was going to enlarge but here is a blog post I came across elsewhere that makes some good points. It is talking about the current effort to recover physical samples from Mars.

Possible result Conclusion
Mars is sterile Life on Earth is unique hypothesis strengthened
Molecules closely related to life on Earth Panspermia, common source for life on Earth and Mars
Evidence of life unrelated to that found on Earth Life evolved separately on Mars, so life is likely to be teeming across the universe
Something else ?

 

Also Robert Shapiro wrote Planetary Dreams in 1999 advocating exploration of space to search for life elsewhere. Shapiro is best known, unfairly I think, as a critic of the RNA world hypothesis and he does touch on that in a chapter "Birth of the RNA World". The approach is more "needs more work" than "nonsense" and a lot of work has been done since 1999.

On 12/9/2021 at 7:37 PM, studiot said:

I am trying not to spoil the series for those who might wish to watch as it was really quite good and explored many issues in a way that only SF can.
Some ideas were drawn from 'A space oddesy' - but were , in my opinion, much better done.

I missed that as I don't subscribe to OCS. I see it's available on Amazon Prime now. Thanks for the info. I'll give it a go.

Edited by Arthur Smith
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The problem of only having the Earth to go by, a single datapoint, is adressed by this guy on youtube, and although I'm a non-mathematician, I think he presents it clearly and well from a mathematical angle, and he claims that you can use maths to get to a real probability result about the existence of life, and the existence of intelligent life.    Well, I liked it enough to watch both, so here are the links, in case you might too :  

https://www.youtube.com/watch?v=PqEmYU8Y_rI  and       https://www.youtube.com/watch?v=iLbbpRYRW5Y   

And apologies if someone has already mentioned them. 

 

 

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