9 ms·

Kepler has certainly made a lot of discoveries. It should be fairly clear to us now that planetary systems are pretty common and, by extension, sentience must (

by cletus 15y ago

Kepler has certainly made a lot of discoveries. It should be fairly clear to us now that planetary systems are pretty common and, by extension, sentience must (by sheer odds) be out there too. But I have to wonder how many assumptions go into this so-called "habitable zone". Doesn't it greatly depend on the atmospheric composition? With a different atmosphere, couldn't Venus be habitable (actually it might be in our Sun's habitable zone)? If Mars were larger, couldn't it support the kind of atmosphere that would allow liquid water. Particularly if such planets were geologically active. Even if all this stacks up, at 600 light years away, like pretty much any other star system, this planet is across a gulf I'm not sure we'll ever cross, which is a somewhat depressing thought.

blhack 15y ago
>sentience must (by sheer odds) be out there too. Why? Sentience just happens to be an evolutionary trait that was beneficial to us, like wings on a bird. There millions of species animals on our planet, and only a handful of them are sentient. We have a bit of a cognitive bias towards thinking that sentient life is something that evolution would work towards, but that isn't really how evolution works.
- RyanMcGreal 15y ago
  It's not anthropocentric to assume that sentience will appear elsewhere in the universe, given the sheer number of opportunities for evolution to solve similar problems in similar ways. I expect sentience to exist in other species for the same reason that birds, bats and flying squirrels have convergent adaptations.
- jarin 15y ago
  Well I mean it runs kind of counter to your argument that there is not just one, but multiple sentient species on the planet. It also didn't take very long in cosmological terms for humans to go from sentient to supercomputers, either.
- maratd 15y ago
  > that isn't really how evolution works. Taking this a step further, finding intelligent life out there is simply impossible. The reason our intelligence is unique to only humans on our planet is largely because we defined intelligence as traits that only we possess. We defined it based on our own nature. Finding life out there that would be socially compatible with us is ridiculously unlikely. That life would have had to spring up in an evolutionary environment identical to ours and that's so unlikely that it might as well be impossible.
  - cryptoz 15y ago
    > Taking this a step further, finding intelligent life out there is simply impossible What? How can you take this position? That's absolutely crazy. Really, you're going to take observations from just a couple of decades and determine that finding something is "impossible"?! No way. There's absolutely no way that finding intelligent life is impossible. > The reason our intelligence is unique to only humans on our planet is largely because we defined intelligence as traits that only we possess Slow down there. Nobody is looking for "human intelligence" on other planets. Maybe that's why you think it's impossible. I'd say dolphins are intelligent. So are some of our computer systems. There's a lot more intelligence that we can recognize that isn't like ours. > Finding life out there that would be socially compatible with us is ridiculously unlikely. I agree. That has nothing to do with intelligence though. > That life would have had to spring up in an evolutionary environment identical to ours and that's so unlikely that it might as well be impossible. identical? Sure, nearly impossible. But why bother making it identical? Do you need 20.946% O2 in the atmosphere? Nope! There are probably billions of planets in the Milky Way alone that could support Earth-like life, if we extrapolate from the Kepler mission data. The chances are better than you might think.
    - maratd 15y ago
      > Slow down there. Nobody is looking for "human intelligence" on other planets. Maybe that's why you think it's impossible. I'd say dolphins are intelligent. So are some of our computer systems. There's a lot more intelligence that we can recognize that isn't like ours. When I think of intelligent alien life, I think along the lines of Klingons, not alien dolphins. Are we going to find alien dolphins? Absolutely. Klingons? Nope.
- marshallp 15y ago
  There's a fundamental flaw in that argument. Once a sentience, or as i would define it, a species capable of creating technology, exists, it is highly likely to not die out as other traits easily can. It only needs to occur once. One could argue it has -almost- occurred on earth many times, including dolphins, elephants, octopus along with apes right now.
  - InclinedPlane 15y ago
    A lot of the more grandiose doom-and-gloom scenarios put forth regarding global warming are a bit overwrought. The Earth will continue to harbor life even if we pumped all of the carbon from every fossil fuel on the planet into the atmosphere. The main issue is that such a world will be different, it may have different species (more of some, less or none of some we've come to know) and it may be more difficult for human civilization to exist. But there's absolutely no risk of human activity re: CO2 emissions in making the Earth uninhabitable.
  - extension 15y ago
    Lots of animals have technology.. beavers, for example.
- rokhayakebe 15y ago
  How can we know if there is life on any planet (close or far) if we can only look for it using our senses? Forget Mars, is it just possible that there is life on earth that we simply cannot know of because we do not have the required senses to perceive it.
  - nitrogen 15y ago
    Physicalism is essential to science. What sense could we (and our instruments) lack that still exists in the physical world? There is no doubt that there are species we have yet to identify and categorize, but those species will still be made of the same matter that comprises the rest of the universe, detectable by the same means. The only major obstacle I see to knowing about some form of life on Earth is location -- we can't scan the entire ocean floor, nor can we penetrate into the mantle.
    - VladRussian 15y ago
      >of the same matter that comprises the rest of the universe, detectable by the same means. man, that plugs nicely into the whole dark matter/energy discussion.
- bluekeybox 15y ago
  > Sentience just happens to be an evolutionary trait that was beneficial to us ... but that isn't really how evolution works. Actually that is how evolution works. Evolution results in species acquiring traits that are beneficial to them. Of course you could make a counter-case that perhaps sentience is only beneficial to us in particular, and not so much to other species -- To which I would completely disagree. There is this fascinating, relatively new theory of how humans became sentient. Previously (1960s) it was thought that humans became sentient either somehow out of the blue or due to having to construct tools etc., which then allowed them to organize into groups. The new theory, on the other hand, claims that high intelligence (and by extension sentience) is an inevitable consequence of living within a particular type of group -- largely the type of group that many primates live in (the original studies were done on baboons), though this is not limited to primates. The idea is that if you are a member of a group where grooming behavior, alliance-making, and status-related interactions are common, you benefit tremendously (in a reproductive sense) from possessing a "theory of mind" capable of making predictions about the actions of others that are at least a few percent more accurate than those of your peers. The way it works is a bit like the stock market -- all you need is to beat the market average. So this "theory of mind" -- being preoccupied with what others think -- is actually claimed to be a runaway effect of the intelligence "arms race" which always occurs among animals living within that type of group. Now, sentience is merely a theory of mind applied to self. I fully expect that within the next 10 million years at least two other mammal species will become sentient, if we humans don't make them extinct that is... Anyone willing to make a long bet?
  - daliusd 15y ago
    I heard theory that there will be no other sentient creatures on Earth because humans will destroy them. I read this theory from article about Birutė Galdikas (http://en.wikipedia.org/wiki/Birut%C4%97_Galdikas http://en.wikipedia.org/wiki/Birut%C4%97_Galdikas) who is studying orangutans. Let's not forget neanderthals as well in this context.
    - deleted 15y ago
      [deleted]
    - 15y ago
ugh 15y ago
If you look at the diagram for the habitable zone in our own solar system you can see that Nasa would class both Mars and Venus as habitable planets. They already place pretty generous bounds around the habitable zone. Given the very real possibility that there could have been (still is?) life on mars that makes a lot of sense. (Nasa just sent Curiosity on its way to Mars and one of its main goals is to look for signs of life.) Still, the only life we currently know of is here on earth. There could be life on Europa, maybe even some other weird places in the solar system but it’s certainly sensible to start with what we know.
- jarin 15y ago
  Both Venus and Mars have good odds of having had liquid water oceans in the past. From what I understand, Venus would possibly be habitable today if it had a carbon cycle and planetary magnetic field to prevent the runaway greenhouse effect.
  - VladRussian 15y ago
    it allows to imagine that something could be a "life" in Venus like conditions as well: "Scientists once thought that no living thing could survive the harsh combination of toxic chemicals, high temperatures, high pressures, and total darkness at these vents. " "Vent bacteria use hydrogen sulfide as their energy source instead of sunlight. " http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/ps_vents.html http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/ps_vents.html
davedx 15y ago
The 'habitable zone' is overly simplistic in general. Look at Europa - it's nowhere near the habitable zone, but is one of the most Earth-like plants in our Solar System. That's just inside the one Solar System we have a fairly complete planetary record of! It also assumes that liquid water and an oxygen atmosphere are prerequisites for life. Extremophiles [1] living on our own planet prove that this is not so. [1] http://en.wikipedia.org/wiki/Extremophile http://en.wikipedia.org/wiki/Extremophile
- CWuestefeld 15y ago
  It also assumes that liquid water and an oxygen atmosphere are prerequisites for life. Extremophiles living on our own planet prove that this is not so. Maybe this is splitting hairs, but we have evidence that life can exist in such extreme condition. We have no evidence that life can arise under those conditions. I think it's perfectly plausible that it's path-dependent: life needs the friendlier conditions to first develop; once it's up and running with a means of evolving, it's able to acclimatize gradually to the extremes. If I'm right, then it's still correct to exclude worlds that could never have had the "correct" conditions.
  - eric-hu 15y ago
    Adding onto this thought, even if life can arise under extreme conditions, the probability of necessary events could still be far lower than the probability of necessary events for life to arise under earth-like conditions. Thus, the habitable zone criteria is simply narrowing the search space to planets with a high(er) probability of developing and supporting life--while discarding planets with a low(er) probability (though some discarded may indeed have life). It seems reasonable to me in this light, as well.
    - majmun 15y ago
      there is probably more chance of finding intelligent life on planet that is not habitable and can't originate life. because once life becomes "intelligent" it will probably try to colonize more than one "uninhabitable" planet by intelligent machines designed for specific environment.
ChuckMcM 15y ago
I find these questions interesting too, when the Global Warming group argues that we have to fix it because climate change caused a great die off, one wonders if we're in the 'habitable zone' for our Sun or if we're in the conditionally habitable zone if the planetary chemistry is correct. The latter would seem to both widen what could be habitable, and narrow the probability that somewhere is habitable (have to both be in a zone and chemically appropriate) As a thought experiment it would be interesting to figure out what it would take to put a satellite in orbit around that planet. One that simply had a plate on it would be fine. Sort of a 'you are not alone' message.
- finnw 15y ago
  What would happen if The Aliens put one of those in orbit around Earth?
  - ChuckMcM 15y ago
    Lots of great Science Fiction has started with that question. Eon comes to mind. [1] https://en.wikipedia.org/wiki/Eon_%28novel%29 https://en.wikipedia.org/wiki/Eon_%28novel%29
    - finnw 15y ago
      I was thinking more along the lines of "we would be intimidated by it, so we should expect the aliens to react the same way, so don't launch it unless you want a war."
- mbell 15y ago
  Skipping the "Global Warming" argument all together the Earth very much in a cold spell in the palaeontological sense[0]. It has been much, much warmer for very long periods of time and really only slightly colder. We're far closer to another ice age than we are to the long term average temperature of the planet, let alone its normal maximum temperature. Generally, the warmer periods have given rise to large ecological growth. Maybe human's won't like it, but consider the amount of diversity that would exist with a near rain forest climate across nearly the entire earth. Note: the horizontal scale is VERY awkward [0]http://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/All_palaeotemps.png/900px-All_palaeotemps.png http://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/All...
Retric 15y ago
A planet's chemistry is influenced by it's size, distance from it's star, the the types of supernova that happened in the region where it formed etc. However, I don't think there is going to be all that much differences between basic planet chemistry. Due to basic physics we are never going to find a 'natural' planet that's 95% pure silver. (Someone could presumably make one though.)
mindstab 15y ago
> sentience must (by sheer odds) be out there too. ... and your solution to the Fermi paradox is?
- jerf 15y ago
  Backing your statement, I'd further observe of all the terms in the Drake equation, the second term "fraction of stars that have planets" is the second least contentious, only behind the first term "average rate of star formation in the galaxy". I don't think I've ever seen someone claim that life on other planets is rare because planets are rare! It's only the later ones that are contentious. As someone who is so skeptical, showing a huge number of planets doesn't cause me to update my probabilities any, as I already anticipated such a huge number of planets.
- pavel_lishin 15y ago
  Time. What are the odds of there being more than one intelligence in the same galactic neighborhood? Looking at our own planet, which is a biodiversity paradise, there's only one strongly sentient, intelligent, tool-using critter - us. Why aren't we surrounded by other tool users trying to communicate with us? Why aren't we chatting with dolphins, working with cephalopods, and commuting to work with chimpanzees? Hell, where are the Neanderthals? They're the only other arguably intelligent species that have co-existed at the same time that we did. It's a big universe, and it's a big timeline.
  - mindstab 15y ago
    > Why aren't we chatting with dolphins Ironic you should say: from HN this morning: Researchers 'speak' to dolphins in their own language http://news.ycombinator.com/item?id=3314056 http://news.ycombinator.com/item?id=3314056 :) And as for time, that's sort of the point of the Fermi paradox, with this much time there should be evidence of life everywhere, unless you have an unstated assumption that all life is self terminating before it reaches a point where it can leave much of a galactic mark? (In our case then, probably excitingly soon)
    - 15y ago
kaybe 15y ago
Planet mass is usually a parameter that we have, even though it does not influence the position of the habitable zone (so Mars is out). The simplest calculation does not involve an atmosphere and just looks at radiative balance from black body radiation and is probably the kind of calculation they're talking about in the article. For getting the real temperature many parameters play a role and most are not available, so they just use a first guess for the habitable zone. An atmosphere will change this radiation balance, with absorptive gases and aerosols blocking radiation (both in- and outgoing) and by distributing the heat more evenly. Atmospheres can be detected if the planet's orbit is good, and it is possible to get an idea about the composition (mainly water, methane and CO2 so far), as well as see changes which are probably due to weather. The method used is to look at the center star's light that travelled through the atmosphere of the planet when it traverses; it's also possible to look at the atmosphere's reflection when the planet is almost behind the star. I can go find some spectra if you're interested. Another important parameter in the equations is albedo ("ability to reflect radiation"). Warmth left from the planet's creation and radioactive decay as well as gravitational effects from other bodies (eg the effect Jupiter has on it's moons) are the other possible energy sources. Geological activity of bigger planets could lead to aurora and allow detection that way, but the instrumentation is not up for that yet.. In our solar system, some moons are considered candidates for life, being covered with a thick layer of ice and possibly containing water underneath and they're not in what is considered the habitable zone of the system. The concept is more of a guideline at this point, really, and also only looks at water (arguably the best candidate for life, but not the only one). </rant> In case you want more information about anything in particular I can find some papers or overviews.
MrScruff 15y ago
I've read this argument a few times and the part I don't follow is how you can figure out the odds for an event (the spontaneous occurrence of life) that has only happened once to our knowledge. For all we know the odds are 1e100 to one.

by cletus 15y ago

blhack 15y ago

>sentience must (by sheer odds) be out there too. Why? Sentience just happens to be an evolutionary trait that was beneficial to us, like wings on a bird. There millions of species animals on our planet, and only a handful of them are sentient. We have a bit of a cognitive bias towards thinking that sentient life is something that evolution would work towards, but that isn't really how evolution works.

RyanMcGreal 15y ago
It's not anthropocentric to assume that sentience will appear elsewhere in the universe, given the sheer number of opportunities for evolution to solve similar problems in similar ways. I expect sentience to exist in other species for the same reason that birds, bats and flying squirrels have convergent adaptations.
jarin 15y ago
Well I mean it runs kind of counter to your argument that there is not just one, but multiple sentient species on the planet. It also didn't take very long in cosmological terms for humans to go from sentient to supercomputers, either.
maratd 15y ago
> that isn't really how evolution works. Taking this a step further, finding intelligent life out there is simply impossible. The reason our intelligence is unique to only humans on our planet is largely because we defined intelligence as traits that only we possess. We defined it based on our own nature. Finding life out there that would be socially compatible with us is ridiculously unlikely. That life would have had to spring up in an evolutionary environment identical to ours and that's so unlikely that it might as well be impossible.
- cryptoz 15y ago
  > Taking this a step further, finding intelligent life out there is simply impossible What? How can you take this position? That's absolutely crazy. Really, you're going to take observations from just a couple of decades and determine that finding something is "impossible"?! No way. There's absolutely no way that finding intelligent life is impossible. > The reason our intelligence is unique to only humans on our planet is largely because we defined intelligence as traits that only we possess Slow down there. Nobody is looking for "human intelligence" on other planets. Maybe that's why you think it's impossible. I'd say dolphins are intelligent. So are some of our computer systems. There's a lot more intelligence that we can recognize that isn't like ours. > Finding life out there that would be socially compatible with us is ridiculously unlikely. I agree. That has nothing to do with intelligence though. > That life would have had to spring up in an evolutionary environment identical to ours and that's so unlikely that it might as well be impossible. identical? Sure, nearly impossible. But why bother making it identical? Do you need 20.946% O2 in the atmosphere? Nope! There are probably billions of planets in the Milky Way alone that could support Earth-like life, if we extrapolate from the Kepler mission data. The chances are better than you might think.
  - maratd 15y ago
    > Slow down there. Nobody is looking for "human intelligence" on other planets. Maybe that's why you think it's impossible. I'd say dolphins are intelligent. So are some of our computer systems. There's a lot more intelligence that we can recognize that isn't like ours. When I think of intelligent alien life, I think along the lines of Klingons, not alien dolphins. Are we going to find alien dolphins? Absolutely. Klingons? Nope.
marshallp 15y ago
There's a fundamental flaw in that argument. Once a sentience, or as i would define it, a species capable of creating technology, exists, it is highly likely to not die out as other traits easily can. It only needs to occur once. One could argue it has -almost- occurred on earth many times, including dolphins, elephants, octopus along with apes right now.
- InclinedPlane 15y ago
  A lot of the more grandiose doom-and-gloom scenarios put forth regarding global warming are a bit overwrought. The Earth will continue to harbor life even if we pumped all of the carbon from every fossil fuel on the planet into the atmosphere. The main issue is that such a world will be different, it may have different species (more of some, less or none of some we've come to know) and it may be more difficult for human civilization to exist. But there's absolutely no risk of human activity re: CO2 emissions in making the Earth uninhabitable.
- extension 15y ago
  Lots of animals have technology.. beavers, for example.
rokhayakebe 15y ago
How can we know if there is life on any planet (close or far) if we can only look for it using our senses? Forget Mars, is it just possible that there is life on earth that we simply cannot know of because we do not have the required senses to perceive it.
- nitrogen 15y ago
  Physicalism is essential to science. What sense could we (and our instruments) lack that still exists in the physical world? There is no doubt that there are species we have yet to identify and categorize, but those species will still be made of the same matter that comprises the rest of the universe, detectable by the same means. The only major obstacle I see to knowing about some form of life on Earth is location -- we can't scan the entire ocean floor, nor can we penetrate into the mantle.
  - VladRussian 15y ago
    >of the same matter that comprises the rest of the universe, detectable by the same means. man, that plugs nicely into the whole dark matter/energy discussion.
bluekeybox 15y ago
> Sentience just happens to be an evolutionary trait that was beneficial to us ... but that isn't really how evolution works. Actually that is how evolution works. Evolution results in species acquiring traits that are beneficial to them. Of course you could make a counter-case that perhaps sentience is only beneficial to us in particular, and not so much to other species -- To which I would completely disagree. There is this fascinating, relatively new theory of how humans became sentient. Previously (1960s) it was thought that humans became sentient either somehow out of the blue or due to having to construct tools etc., which then allowed them to organize into groups. The new theory, on the other hand, claims that high intelligence (and by extension sentience) is an inevitable consequence of living within a particular type of group -- largely the type of group that many primates live in (the original studies were done on baboons), though this is not limited to primates. The idea is that if you are a member of a group where grooming behavior, alliance-making, and status-related interactions are common, you benefit tremendously (in a reproductive sense) from possessing a "theory of mind" capable of making predictions about the actions of others that are at least a few percent more accurate than those of your peers. The way it works is a bit like the stock market -- all you need is to beat the market average. So this "theory of mind" -- being preoccupied with what others think -- is actually claimed to be a runaway effect of the intelligence "arms race" which always occurs among animals living within that type of group. Now, sentience is merely a theory of mind applied to self. I fully expect that within the next 10 million years at least two other mammal species will become sentient, if we humans don't make them extinct that is... Anyone willing to make a long bet?
- daliusd 15y ago
  I heard theory that there will be no other sentient creatures on Earth because humans will destroy them. I read this theory from article about Birutė Galdikas (http://en.wikipedia.org/wiki/Birut%C4%97_Galdikas http://en.wikipedia.org/wiki/Birut%C4%97_Galdikas) who is studying orangutans. Let's not forget neanderthals as well in this context.
  - deleted 15y ago
    [deleted]
  - 15y ago

ugh 15y ago

If you look at the diagram for the habitable zone in our own solar system you can see that Nasa would class both Mars and Venus as habitable planets. They already place pretty generous bounds around the habitable zone. Given the very real possibility that there could have been (still is?) life on mars that makes a lot of sense. (Nasa just sent Curiosity on its way to Mars and one of its main goals is to look for signs of life.) Still, the only life we currently know of is here on earth. There could be life on Europa, maybe even some other weird places in the solar system but it’s certainly sensible to start with what we know.

jarin 15y ago
Both Venus and Mars have good odds of having had liquid water oceans in the past. From what I understand, Venus would possibly be habitable today if it had a carbon cycle and planetary magnetic field to prevent the runaway greenhouse effect.
- VladRussian 15y ago
  it allows to imagine that something could be a "life" in Venus like conditions as well: "Scientists once thought that no living thing could survive the harsh combination of toxic chemicals, high temperatures, high pressures, and total darkness at these vents. " "Vent bacteria use hydrogen sulfide as their energy source instead of sunlight. " http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/ps_vents.html http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/ps_vents.html

davedx 15y ago

The 'habitable zone' is overly simplistic in general. Look at Europa - it's nowhere near the habitable zone, but is one of the most Earth-like plants in our Solar System. That's just inside the one Solar System we have a fairly complete planetary record of! It also assumes that liquid water and an oxygen atmosphere are prerequisites for life. Extremophiles [1] living on our own planet prove that this is not so. [1] http://en.wikipedia.org/wiki/Extremophile http://en.wikipedia.org/wiki/Extremophile

CWuestefeld 15y ago
It also assumes that liquid water and an oxygen atmosphere are prerequisites for life. Extremophiles living on our own planet prove that this is not so. Maybe this is splitting hairs, but we have evidence that life can exist in such extreme condition. We have no evidence that life can arise under those conditions. I think it's perfectly plausible that it's path-dependent: life needs the friendlier conditions to first develop; once it's up and running with a means of evolving, it's able to acclimatize gradually to the extremes. If I'm right, then it's still correct to exclude worlds that could never have had the "correct" conditions.
- eric-hu 15y ago
  Adding onto this thought, even if life can arise under extreme conditions, the probability of necessary events could still be far lower than the probability of necessary events for life to arise under earth-like conditions. Thus, the habitable zone criteria is simply narrowing the search space to planets with a high(er) probability of developing and supporting life--while discarding planets with a low(er) probability (though some discarded may indeed have life). It seems reasonable to me in this light, as well.
  - majmun 15y ago
    there is probably more chance of finding intelligent life on planet that is not habitable and can't originate life. because once life becomes "intelligent" it will probably try to colonize more than one "uninhabitable" planet by intelligent machines designed for specific environment.

ChuckMcM 15y ago

I find these questions interesting too, when the Global Warming group argues that we have to fix it because climate change caused a great die off, one wonders if we're in the 'habitable zone' for our Sun or if we're in the conditionally habitable zone if the planetary chemistry is correct. The latter would seem to both widen what could be habitable, and narrow the probability that somewhere is habitable (have to both be in a zone and chemically appropriate) As a thought experiment it would be interesting to figure out what it would take to put a satellite in orbit around that planet. One that simply had a plate on it would be fine. Sort of a 'you are not alone' message.

finnw 15y ago
What would happen if The Aliens put one of those in orbit around Earth?
- ChuckMcM 15y ago
  Lots of great Science Fiction has started with that question. Eon comes to mind. [1] https://en.wikipedia.org/wiki/Eon_%28novel%29 https://en.wikipedia.org/wiki/Eon_%28novel%29
  - finnw 15y ago
    I was thinking more along the lines of "we would be intimidated by it, so we should expect the aliens to react the same way, so don't launch it unless you want a war."
mbell 15y ago
Skipping the "Global Warming" argument all together the Earth very much in a cold spell in the palaeontological sense[0]. It has been much, much warmer for very long periods of time and really only slightly colder. We're far closer to another ice age than we are to the long term average temperature of the planet, let alone its normal maximum temperature. Generally, the warmer periods have given rise to large ecological growth. Maybe human's won't like it, but consider the amount of diversity that would exist with a near rain forest climate across nearly the entire earth. Note: the horizontal scale is VERY awkward [0]http://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/All_palaeotemps.png/900px-All_palaeotemps.png http://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/All...

Retric 15y ago

A planet's chemistry is influenced by it's size, distance from it's star, the the types of supernova that happened in the region where it formed etc. However, I don't think there is going to be all that much differences between basic planet chemistry. Due to basic physics we are never going to find a 'natural' planet that's 95% pure silver. (Someone could presumably make one though.)

mindstab 15y ago

> sentience must (by sheer odds) be out there too. ... and your solution to the Fermi paradox is?

jerf 15y ago
Backing your statement, I'd further observe of all the terms in the Drake equation, the second term "fraction of stars that have planets" is the second least contentious, only behind the first term "average rate of star formation in the galaxy". I don't think I've ever seen someone claim that life on other planets is rare because planets are rare! It's only the later ones that are contentious. As someone who is so skeptical, showing a huge number of planets doesn't cause me to update my probabilities any, as I already anticipated such a huge number of planets.
pavel_lishin 15y ago
Time. What are the odds of there being more than one intelligence in the same galactic neighborhood? Looking at our own planet, which is a biodiversity paradise, there's only one strongly sentient, intelligent, tool-using critter - us. Why aren't we surrounded by other tool users trying to communicate with us? Why aren't we chatting with dolphins, working with cephalopods, and commuting to work with chimpanzees? Hell, where are the Neanderthals? They're the only other arguably intelligent species that have co-existed at the same time that we did. It's a big universe, and it's a big timeline.
- mindstab 15y ago
  > Why aren't we chatting with dolphins Ironic you should say: from HN this morning: Researchers 'speak' to dolphins in their own language http://news.ycombinator.com/item?id=3314056 http://news.ycombinator.com/item?id=3314056 :) And as for time, that's sort of the point of the Fermi paradox, with this much time there should be evidence of life everywhere, unless you have an unstated assumption that all life is self terminating before it reaches a point where it can leave much of a galactic mark? (In our case then, probably excitingly soon)
  - 15y ago

kaybe 15y ago

Planet mass is usually a parameter that we have, even though it does not influence the position of the habitable zone (so Mars is out). The simplest calculation does not involve an atmosphere and just looks at radiative balance from black body radiation and is probably the kind of calculation they're talking about in the article. For getting the real temperature many parameters play a role and most are not available, so they just use a first guess for the habitable zone. An atmosphere will change this radiation balance, with absorptive gases and aerosols blocking radiation (both in- and outgoing) and by distributing the heat more evenly. Atmospheres can be detected if the planet's orbit is good, and it is possible to get an idea about the composition (mainly water, methane and CO2 so far), as well as see changes which are probably due to weather. The method used is to look at the center star's light that travelled through the atmosphere of the planet when it traverses; it's also possible to look at the atmosphere's reflection when the planet is almost behind the star. I can go find some spectra if you're interested. Another important parameter in the equations is albedo ("ability to reflect radiation"). Warmth left from the planet's creation and radioactive decay as well as gravitational effects from other bodies (eg the effect Jupiter has on it's moons) are the other possible energy sources. Geological activity of bigger planets could lead to aurora and allow detection that way, but the instrumentation is not up for that yet.. In our solar system, some moons are considered candidates for life, being covered with a thick layer of ice and possibly containing water underneath and they're not in what is considered the habitable zone of the system. The concept is more of a guideline at this point, really, and also only looks at water (arguably the best candidate for life, but not the only one). </rant> In case you want more information about anything in particular I can find some papers or overviews.

MrScruff 15y ago

I've read this argument a few times and the part I don't follow is how you can figure out the odds for an event (the spontaneous occurrence of life) that has only happened once to our knowledge. For all we know the odds are 1e100 to one.