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Old 21st August 2019, 05:37 AM   #1
Puppycow
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The frequency of earthlike planets

Interesting new study published recently with relevancy to the Drake equation.

How many Earth-like planets are around sun-like stars?

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Date: August 14, 2019
Source: Penn State
Summary: A new study provides the most accurate estimate of the frequency that planets that are similar to Earth in size and in distance from their host star occur around stars similar to our Sun.
So this study is billed as the best estimate to date of the number of "earth-like" planets in orbit around "sun-like" stars.

If you are wondering how those terms are defined for purposes of the research, a sun-like star is an FGK star (link) and an earth-like planet is a planet "from three-quarters to one-and-a-half times the size of earth, with orbital periods ranging from 237 to 500 days". So basically a planet roughly the size of the earth, roughly in a similar orbit to the earth, around a star roughly the size of our own sun.

So their middle estimate is one in four, with one in two at the high end of the range and one in 33 at the low end. So that seems pretty common.

Obviously, to be sure, those parameters do not mean that all or even most of those hypothetical planets would be hospitable to life as we know it. Many are probably closer to Venus or to Mars. But if as a wild guess, 1 in 10 is more like earth than Mars or Venus? What would that imply about the frequency of planets where life is possible?

Never mind intelligent life. If anything, I think it would be cool if the first planet we discover with extraterrestrial life doesn't have an intelligent species like us. That way it wouldn't be a threat and if we could somehow get people there (I know, not easy) we could be the dominant species and just think of all the scientific things we could learn.
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Old 21st August 2019, 05:44 AM   #2
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I heard about this on SGU last weekend. Surprising, but very welcome indeed
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Old 21st August 2019, 05:58 AM   #3
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Originally Posted by lionking View Post
I heard about this on SGU last weekend. Surprising, but very welcome indeed
Me too. I learn a lot of interesting things listening to them. Do they pronounce Melbourne correctly though?
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Old 21st August 2019, 06:04 AM   #4
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How many of these planets could be life bearing is really hard to estimate, mainly due to the fact that we only have one data point to go on for what life bearing planets are like.

There are a ton of unanswered questions, most of which won't get answers until we can reliably measure the atmospheric constituents of some of these planets. It's something that researchers have been working on for several years now, but it ain't easy.
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Old 21st August 2019, 06:15 AM   #5
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Originally Posted by wollery View Post
How many of these planets could be life bearing is really hard to estimate, mainly due to the fact that we only have one data point to go on for what life bearing planets are like.

There are a ton of unanswered questions, most of which won't get answers until we can reliably measure the atmospheric constituents of some of these planets. It's something that researchers have been working on for several years now, but it ain't easy.
If I understand correctly that should get a lot easier with some of the new telescopes that should be coming online in the next decade or so, right? James Webb? But also several others?
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Old 21st August 2019, 06:32 AM   #6
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My assumption is that, for life, an earth sized planet in the right zone is required. Additionally, I believe that the planet requires a moon in almost exactly the same spot as ours is, carved off in exactly the same way as ours, in a large impact that peeled off a load of planet to make a moon.

I believe that life can only exist toughly this far out from galactic centre and absolutely requires at least two gas giants sharing the orbit to protect the poor little rock from asteroid collision.

I believe that all of these things and many more are required for life to even be a possibility and that the earth is all but unique in producing life.
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Old 21st August 2019, 08:05 AM   #7
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Originally Posted by Roboramma View Post
If I understand correctly that should get a lot easier with some of the new telescopes that should be coming online in the next decade or so, right? James Webb? But also several others?
Yes, the various 30m ones.

But perhaps more important will be the new instruments attached to the telescopes (not just the new ones, also existing ones like the VLT) ... various adaptive optics gadgets will feed really spiffy spectrometers, for example.
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Old 21st August 2019, 08:11 AM   #8
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Originally Posted by 3point14 View Post
My assumption is that, for life, an earth sized planet in the right zone is required. Additionally, I believe that the planet requires a moon in almost exactly the same spot as ours is, carved off in exactly the same way as ours, in a large impact that peeled off a load of planet to make a moon.

I believe that life can only exist toughly this far out from galactic centre and absolutely requires at least two gas giants sharing the orbit to protect the poor little rock from asteroid collision.

I believe that all of these things and many more are required for life to even be a possibility and that the earth is all but unique in producing life.
If we find fossils on Mars, even if only of something like bacteria; if we find life in the Europan ocean, or in whatever liquid water there is under the surface of Enceladus; if ... we will learn that life my arise in many different environments, several homeworlds of which, outside our own solar system, will be hard to detect, let alone assess for life.
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Old 21st August 2019, 08:26 AM   #9
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Originally Posted by JeanTate View Post
If we find fossils on Mars, even if only of something like bacteria; if we find life in the Europan ocean, or in whatever liquid water there is under the surface of Enceladus; if ... we will learn that life my arise in many different environments, several homeworlds of which, outside our own solar system, will be hard to detect, let alone assess for life.


I appreciate that. I hold my position mostly out of contrariness.

Every time someone postulates that life is likely to be prevalent throughout the universe I like to point out that we have one data point which, by itself, is statistically insignificant - it is literally impossible to draw any conclusions from a single data point.

The bottom line is we have no clue, unless and until we find what you describe above we have zero method of accurately predicting how often life appears in the universe. We're guessing.

Because everyone seems to like to guess that it's everywhere, I like to guess that it's almost nowhere. Just to be contrary.
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Old 21st August 2019, 08:39 AM   #10
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Originally Posted by 3point14 View Post
I appreciate that. I hold my position mostly out of contrariness.

Every time someone postulates that life is likely to be prevalent throughout the universe I like to point out that we have one data point which, by itself, is statistically insignificant - it is literally impossible to draw any conclusions from a single data point.

The bottom line is we have no clue, unless and until we find what you describe above we have zero method of accurately predicting how often life appears in the universe. We're guessing.

Because everyone seems to like to guess that it's everywhere, I like to guess that it's almost nowhere. Just to be contrary.
Some of us really hope that you're right:

https://nickbostrom.com/extraterrestrial.pdf
Quote:
But I hope that our Mars probes will discover nothing. It would be good news if we find Mars to be completely sterile. Dead rocks and lifeless sands would lift my spirit.

Conversely, if we discovered traces of some simple extinct life form—some bacteria, some algae—it would be bad news. If we found fossils of something more advanced, perhaps something looking like the remnants of a trilobite or even the skeleton of a small mammal, it would be very bad news. The more complex the life we found, the more depressing the news of its existence would be. Scientifically interesting, certainly, but a bad omen for the future of the human race.
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Old 21st August 2019, 08:43 AM   #11
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Originally Posted by Roboramma View Post
Some of us really hope that you're right:

https://nickbostrom.com/extraterrestrial.pdf
I wholly disagree with the author. First of all, we know the sun's going out in a few billion years so unless we A) survive to that point and B) get the hell out of here, the future is already grim. Also, that one planet saw the end of its ecosystem has nothing to do with us. Plenty of planets, I'm sure, are now lifeless that used to not be.
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Old 21st August 2019, 08:51 AM   #12
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Originally Posted by 3point14 View Post
I appreciate that. I hold my position mostly out of contrariness.

Every time someone postulates that life is likely to be prevalent throughout the universe I like to point out that we have one data point which, by itself, is statistically insignificant - it is literally impossible to draw any conclusions from a single data point.

The bottom line is we have no clue, unless and until we find what you describe above we have zero method of accurately predicting how often life appears in the universe. We're guessing.

Because everyone seems to like to guess that it's everywhere, I like to guess that it's almost nowhere. Just to be contrary.
Indeed.

Note that, if there is, or once was, life under the surface of Enceladus - a small moon of a gas giant - it will likely be centuries before we could even detect such moons orbiting an exoplanet, and millennia before we could put realistic constraints on the likelihood of life. However, getting an answer as to whether there is life on/in Enceladus may take mere decades (“was” will be harder to answer, but still more likely decades than centuries).
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Old 21st August 2019, 08:52 AM   #13
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It'd be rather funny if we eventually find that eighteen of the solar system's planets or moons have harbored or are harboring some sort of life.

That would sure change our outlook of where it could be found.
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Old 21st August 2019, 07:57 PM   #14
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Originally Posted by Puppycow View Post
Me too. I learn a lot of interesting things listening to them. Do they pronounce Melbourne correctly though?
Apart from rhoticising the R, they get pretty close.
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Old 21st August 2019, 07:59 PM   #15
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Originally Posted by 3point14 View Post
My assumption is that, for life, an earth sized planet in the right zone is required. Additionally, I believe that the planet requires a moon in almost exactly the same spot as ours is, carved off in exactly the same way as ours, in a large impact that peeled off a load of planet to make a moon.

I believe that life can only exist toughly this far out from galactic centre and absolutely requires at least two gas giants sharing the orbit to protect the poor little rock from asteroid collision.

I believe that all of these things and many more are required for life to even be a possibility and that the earth is all but unique in producing life.
As, when life emerged, the moon was nowhere near where it now is, I think that assumption is mistaken.
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Old 21st August 2019, 08:19 PM   #16
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An arXiv article up today (dated tomorrow) is intriguing ... it is a proposal to send a mission to Ceres. Among other aims, to look for evidence of past (even current) environments conducive to life.

I’ll post a link later.
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Old 21st August 2019, 10:13 PM   #17
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Originally Posted by 3point14 View Post
My assumption is that, for life, an earth sized planet in the right zone is required. Additionally, I believe that the planet requires a moon in almost exactly the same spot as ours is, carved off in exactly the same way as ours, in a large impact that peeled off a load of planet to make a moon.

I believe that life can only exist toughly this far out from galactic centre and absolutely requires at least two gas giants sharing the orbit to protect the poor little rock from asteroid collision.

I believe that all of these things and many more are required for life to even be a possibility and that the earth is all but unique in producing life.

Seconded. I'd also like to point out that the Milky Way Galaxy is ours for the taking!!
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Old 22nd August 2019, 12:07 AM   #18
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Originally Posted by Belz... View Post
I wholly disagree with the author. First of all, we know the sun's going out in a few billion years so unless we A) survive to that point and B) get the hell out of here, the future is already grim.
Sure, but some of us are optimists. The point is that the lack of evidence of alien life out there in the galaxy should quell that optimism about the likelihood of "get[ting] the hell our of here", unless we've already passed whatever the improbable step is on the way to that.

If you already think that getting the hell out of here is unlikely, well, there's not much more to worry about.

Quote:
Also, that one planet saw the end of its ecosystem has nothing to do with us. Plenty of planets, I'm sure, are now lifeless that used to not be.
If intelligent life has arisen many times but never spread throughout the galaxy, then it's very unlikely that we will spread throughout the galaxy. If, on the other hand, intelligent life hasn't arisen before then the fact that it hasn't spread throughout the galaxy doesn't give us any information about the how likely we are to spread throughout the galaxy.

If you are optimistic about the likelihood that we will spread throughout the galaxy, then finding life elsewhere can dim that optimism, for this reason.

Further, if intelligent life arose many times but didn't spread, there should be some explanation for it's not spreading. It may be something banal, like that interstellar travel/colonisation is simply too difficult (I don't think), or uneconomical (maybe), but another possibility is that intelligent life just doesn't tend to last long enough to start that process.
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Old 22nd August 2019, 12:15 AM   #19
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Kurzgesagt has a good summary of the Fermi Paradox which covers most of the important points.

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Old 22nd August 2019, 01:35 AM   #20
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Originally Posted by sphenisc View Post
As, when life emerged, the moon was nowhere near where it now is, I think that assumption is mistaken.
I stand corrected.
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Old 22nd August 2019, 02:18 AM   #21
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My personal belief, is an extreme take on the "Rare Earth Hypothesis" and in turn, that life of the humanoid sentient type exists ONLY on earth ... and there are no other life forms like us.
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Old 22nd August 2019, 05:03 AM   #22
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There is a whole range of life, from very simple life forms to very complex animals. I think if we explore the galaxy we will find simple life forms to be common, but the more complex forms of life to be much more rare as better conditions need to exist for them to evolve.
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Old 22nd August 2019, 05:07 AM   #23
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Originally Posted by Roboramma View Post
If intelligent life has arisen many times but never spread throughout the galaxy, then it's very unlikely that we will spread throughout the galaxy.
Right, I meant life in general.

Quote:
If you are optimistic about the likelihood that we will spread throughout the galaxy, then finding life elsewhere can dim that optimism, for this reason.
Well, I'm somewhat optimistic about it, but the possibility you mention doesn't dampen it at all.

Quote:
Further, if intelligent life arose many times but didn't spread, there should be some explanation for it's not spreading.
Internet. It's the stupid internet they all come up with. They become stuck in the virtual world, stop innovating and die out plugged to their machines.
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Old 22nd August 2019, 06:56 AM   #24
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Originally Posted by Roboramma View Post
Further, if intelligent life arose many times but didn't spread, there should be some explanation for it's not spreading. It may be something banal, like that interstellar travel/colonisation is simply too difficult (I don't think), or uneconomical (maybe), but another possibility is that intelligent life just doesn't tend to last long enough to start that process.

My guess is that, if there is any other life out there (doubtful) then it mostly arises on planets that are too dense for things to leave from.
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Old 22nd August 2019, 07:01 AM   #25
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Maybe it's the inhabitants who are too dense.
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Old 22nd August 2019, 08:16 AM   #26
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Originally Posted by Belz... View Post
Right, I meant life in general.



Well, I'm somewhat optimistic about it, but the possibility you mention doesn't dampen it at all.
It's not clear to me whether or not you follow the logic from the link. Do you think you could explain what he said in your own words? I think that would help the conversation.



Quote:
Internet. It's the stupid internet they all come up with. They become stuck in the virtual world, stop innovating and die out plugged to their machines.
Jokes aside I actually think that's a pretty strong possibility.
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Old 22nd August 2019, 08:44 AM   #27
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Originally Posted by Roboramma View Post
Further, if intelligent life arose many times but didn't spread, there should be some explanation for it's not spreading. It may be something banal, like that interstellar travel/colonisation is simply too difficult (I don't think), or uneconomical (maybe), but another possibility is that intelligent life just doesn't tend to last long enough to start that process.
I personally think that the difficulty of interstellar travel is probably a huge bottleneck. I practically despair when I think of all the difficulties involved. 20 light years may as well be a billion light years. Physically transporting living people in a spaceship across such distances that is.
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Old 22nd August 2019, 08:55 AM   #28
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Originally Posted by Puppycow View Post
I personally think that the difficulty of interstellar travel is probably a huge bottleneck. I practically despair when I think of all the difficulties involved. 20 light years may as well be a billion light years. Physically transporting living people in a spaceship across such distances that is.
You might be right. On the other hand: we usually think about this problem with certain constraints in mind, for instance a human lifespan. But there's no reason that lifespans couldn't be extended indefinitely. I also don't really think there's much reason to send manned interstellar missions. We haven't had a manned mission further than the moon, but we've had probes to every planet, and our robotic technology will only improve.

Also, I recently read Project Orion by George Dyson, and the idea of nuclear pulse propulsion has a lot more going for it than I had realised.

Finally, to some extent the difficulties of interstellar travel can be overcome by just extending your time scale. The stars are all already moving relative to one another. Rather than travelling to another star, why not just wait for it to come to you?
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Old 22nd August 2019, 08:58 AM   #29
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Originally Posted by Roboramma View Post
It's not clear to me whether or not you follow the logic from the link. Do you think you could explain what he said in your own words? I think that would help the conversation.
I'm following the logic that you posted. If we discover dead lifeforms everywhere somehow it makes out odds of expanding outside of Earth more grim. I don't agree, especially in the general case. If we find traces of dead civilisations it might be more indicative.

Quote:
Jokes aside I actually think that's a pretty strong possibility.
I was actually serious.
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Old 22nd August 2019, 09:21 AM   #30
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Originally Posted by Belz... View Post
I'm following the logic that you posted. If we discover dead lifeforms everywhere somehow it makes out odds of expanding outside of Earth more grim. I don't agree, especially in the general case. If we find traces of dead civilisations it might be more indicative.
Right, I'm asking if you can express why Bostrom thinks finding life everywhere would make the odds of expanding outside earth more grim.



Quote:
I was actually serious.
Well, in that case we agree.
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Old 22nd August 2019, 09:23 AM   #31
Belz...
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Originally Posted by Roboramma View Post
Right, I'm asking if you can express why Bostrom thinks finding life everywhere would make the odds of expanding outside earth more grim.
I didn't read the PDF. I can't even download it. I just went from the post you made.
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Old 22nd August 2019, 10:25 AM   #32
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Originally Posted by 3point14 View Post
I appreciate that. I hold my position mostly out of contrariness.

Every time someone postulates that life is likely to be prevalent throughout the universe I like to point out that we have one data point which, by itself, is statistically insignificant - it is literally impossible to draw any conclusions from a single data point.

The bottom line is we have no clue, unless and until we find what you describe above we have zero method of accurately predicting how often life appears in the universe. We're guessing.

Because everyone seems to like to guess that it's everywhere, I like to guess that it's almost nowhere. Just to be contrary.
Yeah dat. I don't know how "the most accurate estimate" is defined. Because The Amazing Kreskin says so?
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Old 22nd August 2019, 10:27 AM   #33
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Arthur C Clarke? "there's billions of planets out there. Perhaps only one in a million has life? Either way it is astounding."
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Old 22nd August 2019, 01:28 PM   #34
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The Fermi Paradox has already been solved:

https://www.smbc-comics.com/comic/monkey
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Old 22nd August 2019, 02:12 PM   #35
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Originally Posted by wollery View Post
How many of these planets could be life bearing is really hard to estimate, mainly due to the fact that we only have one data point to go on for what life bearing planets are like.

There are a ton of unanswered questions, most of which won't get answers until we can reliably measure the atmospheric constituents of some of these planets. It's something that researchers have been working on for several years now, but it ain't easy.
One known planet with life, but we know a lot from this planet besides Life: Y/N?

1) Life formed almost as soon as conditions emerged that life could exist in.
If abiogenesis were the result of some rare coincidence of the right things coming together, one would not expect to see life developing so soon geologically speaking.
2) Life exists and has adapted to incredibly diverse extremes all over the planet.

Our one example contains a wealth of information.
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Old 22nd August 2019, 02:16 PM   #36
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Originally Posted by 3point14 View Post
My assumption is that, for life, an earth sized planet in the right zone is required. Additionally, I believe that the planet requires a moon in almost exactly the same spot as ours is, carved off in exactly the same way as ours, in a large impact that peeled off a load of planet to make a moon.

I believe that life can only exist toughly this far out from galactic centre and absolutely requires at least two gas giants sharing the orbit to protect the poor little rock from asteroid collision.

I believe that all of these things and many more are required for life to even be a possibility and that the earth is all but unique in producing life.
Sure, "common" is relative. I agree, not only should we be looking for planets in the Goldilocks Zone relative to their star, but also relative to the location within the galaxy and probably a planet with water and tides, though I'm not positive that the tides are crucial.

As for almost nowhere though, have you seen the Hubble Deep Field? If there was only one planet with life per 100 galaxies, there would still be billions of planets with life.
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Old 22nd August 2019, 03:23 PM   #37
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Originally Posted by Skeptic Ginger View Post
One known planet with life, but we know a lot from this planet besides Life: Y/N?

1) Life formed almost as soon as conditions emerged that life could exist in.
If abiogenesis were the result of some rare coincidence of the right things coming together, one would not expect to see life developing so soon geologically speaking.
2) Life exists and has adapted to incredibly diverse extremes all over the planet.

Our one example contains a wealth of information.
I agree with this. It's certainly true that one planet is only one planet, but I think we can infer a few things from our own planet. One of those things is probably that so-called intelligent life, if we define that as a technological species like ourselves, it probably relatively rare, even on planets that support life. Because it takes a long time to evolve to that point and the planet has to maintain the conditions that allow life to exist for billions of years to maybe get one "intelligent" species.
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Old 22nd August 2019, 05:48 PM   #38
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Originally Posted by Skeptic Ginger View Post
One known planet with life, but we know a lot from this planet besides Life: Y/N?

1) Life formed almost as soon as conditions emerged that life could exist in.
If abiogenesis were the result of some rare coincidence of the right things coming together, one would not expect to see life developing so soon geologically speaking.
2) Life exists and has adapted to incredibly diverse extremes all over the planet.

Our one example contains a wealth of information.
This is why I'm virtually certain that there is life elsewhere.
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Old 22nd August 2019, 07:53 PM   #39
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Originally Posted by Elagabalus View Post
Seconded. I'd also like to point out that the Milky Way Galaxy is ours for the taking!!
The Romulans have a different opinion.
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Old 22nd August 2019, 11:00 PM   #40
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Originally Posted by Belz... View Post
It'd be rather funny if we eventually find that eighteen of the solar system's planets or moons have harbored or are harboring some sort of life.
You know what would be even funnier? It it turned out the 'alien' life actually came from Earth.
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