People sometimes ask why we are spending so much time searching for planets that are so far away. The question refers to the Kepler mission and the fact that the distance to its target stars is generally 600 to 3,000 light years. In fact, fewer than one percent of the stars Kepler is examining out along the Orion arm are closer than 600 light years. The reason: Kepler is all about statistics, and our ability to learn how common exoplanets and in particular terrestrial planets are in the aggregate. The last thing the Kepler team is thinking about is targets for a future interstellar probe.
Studies of closer stars continue — we have three ongoing searches for planets around the Alpha Centauri stars, for example. But there is so much we still have to learn about the overall disposition of planets in our galaxy. New work by an international team of astronomers involves gravitational microlensing to answer some of these questions, and the results suggest that planets — even warm, terrestrial ones — are out there in vast numbers. Here again statistical analysis plays a crucial role, in conjunction with other forms of exoplanet detection. Arnaud Cassan (Institut d?Astrophysique de Paris) is lead author of the paper on this work in Nature:
“We have searched for evidence for exoplanets in six years of microlensing observations. Remarkably, these data show that planets are more common than stars in our galaxy. We also found that lighter planets, such as super-Earths or cool Neptunes, must be more common than heavier ones.”
Gravitational microlensing is yet another tool in the exoplanet hunt, and an extremely useful one because it gets around some of the limitations of the other major methods. Radial velocity studies tend to favor large planets that are close to their star, although with time and improving techniques, we’re using RV to learn about smaller and more distant worlds. Transit studies like Kepler’s are powerful but take time, as we wait for lengthy planetary orbits to be completed and confirm the presence of planets suggested by slight dips in starlight. But microlensing can detect planets over a wide mass range and also spot planets much further from their stars.
Image: The Milky Way above the dome of the Danish 1.54-metre telescope at ESO’s La Silla Observatory in Chile. The central part of the Milky Way is visible behind the dome of the ESO 3.6-metre telescope in the distance. On the right the Magellanic Clouds can be seen. This telescope was a major contributor to the PLANET project to search for exoplanets using microlensing. The picture was taken using a normal digital camera with a total exposure time of 15 seconds. Credit: ESO/Z. Bardon/ProjectSoft.
The current work uses data from the PLANET and OGLE microlensing teams, two studies that rely on a foreground star magnifying the light of a much more distant star lined up behind it. If the lensing star also has an orbiting planet, the planet’s effect in brightening the background star is measurable. The method gives us the chance to look for planets at a wide range of distances from the Earth, but it also relies on purely chance alignments that are obviously rare. In fact, from 2002 to 2007, only 3247 such events were identified, with 500 studied at high resolution. All this from a microlensing search that involved millions of stars.
The researchers combined the PLANET and OGLE data with detections from earlier microlensing work and weighed these against non-detections during the six year period of study. They then analyzed these data in conjunction with radial velocity and transit findings. The result: Given the odds against finding planets through these chance celestial alignments, planets must be abundant in the Milky Way. In fact, the researchers conclude that one in six of the stars studied hosts a planet with a Jupiter-class companion, half have planets of Neptune’s mass and two-thirds are likely to have super-Earths. Note that the survey was sensitive to planets with masses ranging from five times the Earth’s up to ten times the mass of Jupiter.
Uffe Gråe Jørgensen is head of the research group in Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen:
“Our microlensing data complements the other two methods by identifying small and large planets in the area midway between the transit and radial velocity measurements. Together, the three methods are, for the first time, able to say something about how common our own solar system is, as well as how many stars appear to have Earth-size planets in the orbital area where liquid water could, in principle, exist as lakes, rivers and oceans — that is to say, where life as we know it from Earth could exist in principle.”
Jørgensen goes on to conclude that out of the Milky Way’s 100 billion stars, there are about 10 billion with planets in the habitable zone, “…billions of planets with orbits like Earth and of comparable size to the Earth.” Daniel Kubas (ESO, and co- lead author of the paper), takes all this into account and concludes: “We used to think that the Earth might be unique in our galaxy. But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way.” Statistics tell the tale, one that will be refined with each new exoplanet detection, but one that points increasingly to a galaxy where Earth-sized planets are common.
The paper is Cassan, Kubas et al., “One or more bound planets per Milky Way star from microlensing observations,” Nature 481, 167–169 (12 January 2012). Abstract available.
Rob and Eniac
Good point about the tendancy for increased complexity and parrallel evolution of various characteristics. My reference to a random walk certainly wasnn’t intended as a comphrehensive discussion of evolution! Rather, in passing, the discussion around the probability of technological civilisations emerging had made me think about the underlying mechanisms. Mutations could be rather crudely considered as a random walk (very crudely I know, but bear with me…) Lets’ take a specific characteristic such as intelligence. In a very simplistic sense this could be considered a variable that has a contraint of zero as a minimum value and (I presume) no upper limit.
In order for intelligence to begin to appear there needs to be quite a range of preconditions satisfied. I am no expert on this, so don’t intend to try to list them all, but for example it requires multicellular organisms etc etc.
Next, once preconditions are met, mutations (the random walk aspect I was thinking about) take place which may act to increase or decrease intelligence from time to time. The path of evolutionary development is, as you quite rightly say, by no means random in that these random mutations are then selected for in terms of fitness to survive. This may produce the appearance of a trend in some characteristics over time in specific lineages. In other organisms which do not have the preconditions for the trait to appear or where the selection value in broadly neutral, or possibly negative, the characteristic will tend to not show much if any evidence of trends (e.g. micro-organisms and intelligence as an example).
Selection occurrs at the level of the organism – it lives and reproduces or not. A change in one characteristic such as intelligence may well only be useful in survival terms if other characteristics are also present to allow it to used effectively (or more so than the competition) – which may well relate to the parrallel aspects of evolution of different characteristics you refer to.
Why I mentioned it in passing but didn’t develop the thought in the earlier post, and was therefore probably too vague in the way I wrote it, was that I was pondering the possibility that some insight might be obtained from looking at the rather large sample we have here on earth of speciation events for DNA based life in an earth like environment. This seems to show that apparent ‘trends’ in characteristics can move relatively quickly once the preconditions for their useful appearance are in place and there is a selection value. The problem of course is that we only have a sample of one in terms of the length of time it takes for some of the really key steps, such as multicellular organisms etc. to appear. This may have happened unusually quickly, slowly or anything in between on earth. This then led to the thought around what level of computing power it would need to actually model evolution in a more realistic sense rather than a purely statistical sense – on that I have absolutely no idea!
I have noticed that as we make more discoveries and improve our predictions about the nature of the Universe in regards to whether extraterrestrial life exists or not, the crowd that does not think anyone else is out there past Earth remains steadfast despite the growing evidence.
Dozens of complex organic molecules found throughout space. Life appears relatively quickly on the very ancient Earth and has since been found thriving in extreme locations. Thousands of exoplanets detected and now there may be hundreds of billions of them in the Milky Way galaxy alone. For those who think Earth life is unique or practically so, this scientific evidence is never good enough, no matter how many real data points we plug into the Drake Equation.
While there is of course the possibility that no alien life exists beyond our pale blue dot, it also seems that many of those who deny the existence of extraterrestrials have agendas that are political and religious, not scientific.
Despite several centuries of scientific evidence, many people continue to deny that organisms on this planet appeared and developed via natural evolution. Instead they insist that the world and life could only come into being through a supernatural deity, a claim that requires no empirical proof and in fact often thrives on being supported by faith alone.
As for the political angle, while I doubt many politicians and other types of leaders give much thought to the idea of ETI and alien life in general if at all, I am also sure few of them would want even the possibility of a superior and more powerful species existing in the galaxy that could one day remove them from their positions of authority, either deliberately or by dissolving the confidence of their Earthly followers.
So the next time we are told by some authority figure that they don’t think alien beings of any stripe could exist despite the incredible amount of worlds and ingredients for life in just our galaxy alone, check their background to see if they are being scientifically objective or not. Being entitled to one’s opinion is one thing, but when it comes from a less than educated realm this only hampers science and knowledge.
Thousands of years of fear and ignorance have kept humanity from being much further along in terms of technological advancements and cosmic awareness than we are at present.
Nick and Rob Henry; with regard to cost: I read a guesstimate of some 1 trillion USD (Net Present Value) for a 1000 km2 O’Neill colony, so my 100 billion was generous.
The asteroid belt may be easily exploitable because of its fragmented nature and near-absemce of gravity, however, this fragmented nature also poses a problem: the entire belt only contains about 1% orso of the earthmass, half the moon’s mass, and all abjects above 1 meter diameter combined only on the order of 10% of the moon’s mass. Scattered over a huge area. Only a limited number of asteroids are really interesting for exploitation.
Still interesting, but I doubt whether that material will house billions, let alone trillions. Furthermore, overcoming gravity and transport are only a part of total construction and maintenance cost and for high tech stuff only a very small fraction. The actual building and maintaining will take by far the lion’s share of investment.
I seriously doubt whether this cost will ever come down enough in any foreseeable future for any ‘ordinary’ production in space (such as food) to be anywhere near competitive with production of the same on earth. In other words, even with sufficient capital and technology it will nearly always be far cheaper (capital, energy) to produce the same products on earth, even if we have to make the Sahara fertile for it.
Don’t misunderstand me here: I am not questioning a future with space stations here, not even large ones, for research and maybe a few very valuable specialty products, but I am indeed questioning the use of space stations for large-scale production of common products for earthly consumption (as Rob was suggesting). Besides, when doing this, the earth gravity well which was first avoided in production again becomes a problem in export/import.
In-space production of ‘common’ products for the indigenous space population itself, ok, but again the same issue arises: why would you maintain a large space-based population, if the same population can be maintained much cheaper on earth (or another planet)?
This still does not even address the fact that, even with a space-based population and production, certain materials will still have to be hauled from earth for quite a while, i.e. it may take a long time before space-stations/colonies become truly self-sufficient, if ever.
With regard to long-term stability: though it is true that objects in space are not subject to the same erosive forces as objects on a planet, space stations and colonies will be very complex structures that are not near any natural equilibrium or natural self-sustaining system (e.g. atmosphere, water cycle), hence they will inevitable have to be maintained and renewed. In this respect it is rather irrelevant whether their average lifespan would be 1000 or 10,000 years.
Planets, on the other hand, may sometimes be rather cruel to human constructions, however, they have great intrinsic (natural) stability and self-sustenance, which also makes them so particularly suitable as long-term platforms for life.
Numeric example:
If we reasonably assume;
For a planet: 1 gy of inhabitable lifespan, 100 million km2 of living space, 1 trillion (1000 billion) USD total cost of interstellar mission;
For a space colony: 1000 yr inhabitable lifespan (before complete replacement, which may take place in stages), 1000 km2 of living space, 100 billion USD for construction plus maintenance;
Result: the planet is 10^10 times (ten billion, sic!) cheaper than the space colony per ‘square kilometer year’.
Even if we assumed a ridiculously short habitable lifespan for the planet of 1 million years (lousy planet), a generous 10,000 years for the space colony, and a ridiculously cheap 10 billion USD including maintenance for the same (that’s 10 USD per square meter, heck, building the cheapest houses or maintaining offices on earth is much more expensive!), the ratio is still 10^5 (one hundred thousand) in favour of planets.
Morale: planets are dirt cheap and very dependable (once you manage to get there and do the refurbishing where necessary).
Eniac said on January 17, 2012 at 23:15:
“Also, in your statement you imply that nuclear war precludes survival. This, as others have pointed out, is not true. Unless you speak about the political systems we call nations, which may indeed not survive. Even our technological economy may be set back substantially, bombed back to the proverbial Dark Ages, or even the Stone Age. Humanity, on the other hand, is very unlikely to find its complete demise in this way. And any subsequent recovery will be fast, because artifacts, know-how, and even just the example of history will be there to help.”
LJK replies:
I invite you and everyone else to read the classic science fiction work A Canticle for Leibowitz by Walter M. Miller, Jr.:
http://public.wsu.edu/~brians/science_fiction/canticle.html
Eniac said on January 17, 2012 at 23:15:
“Also, in your statement you imply that nuclear war precludes survival. This, as others have pointed out, is not true. Unless you speak about the political systems we call nations, which may indeed not survive. Even our technological economy may be set back substantially, bombed back to the proverbial Dark Ages, or even the Stone Age. Humanity, on the other hand, is very unlikely to find its complete demise in this way. And any subsequent recovery will be fast, because artifacts, know-how, and even just the example of history will be there to help.”
LJK replies:
I want to add: If we cannot seem to get our acts together about a number of important matters, especially the technological and infrastructural ones regarding space exploration and colonization, while our civilization is in essentially running order, how do you expect it to happen when our society is taken down by nuclear war?
Do not imagine things will be like they were after World War 2. A full-scale nuclear war will wipe out most if not all of the major cities around the globe, plus radiation and wildfires will despoil most of the surrounding lands. And this is not even mentioning the possibility for nuclear winter. Should things go as badly as they are predicted to, we will be lucky if there is even a monastery left where monks preserve the few fragments of our civilization.
“Mr. President, I’m not saying we wouldn’t get our hair mussed. But I do say no more than ten to twenty million killed, tops. Uh, depending on the breaks.” – General “Buck” Turgidson in Dr. Strangelove: Or How I Learned to Stop Worrying and Love the Bomb (1963)
“And any subsequent recovery will be fast, because artifacts, know-how, and even just the example of history will be there to help.”
That might have been true , exept for one tiny little detail : many of the easy-to-get rawmaterials will be close to running out . A plausible scenario would bee for a series of escalating nuclear wars to start in 50 years , at a time where consumpetion of rawmaterials is 3 times as big as now .
Sorry Anthony, but I couldn’t resist your challenge. You said “In order for intelligence to begin to appear there needs to be quite a range of preconditions satisfied… for example it requires multicellular organisms“.
Okay that seems obvious, but first we must remember their nervous systems cannot form connected neurons, so almost all their intelligent decision making potential must be held internally amount its macromolecules. Now, in turn, most of this is held by molecules that have the potential to switch internal modes, and we should check if that can lead to intelligence. It may come as a surprise to you to find that many protozoa have long been recognised as able to learn and be trained, but it came as a surprise to me to find that that is also true of at least one bacterium.
http://www.nature.com/news/2008/080508/full/news.2007.360.html
Now for your later “obvious truth”. You gave microbes as an example where no increase of intelligence with evolution could be shown. Not so. The number of signal transduction proteins scales with the square of the size of the total genome.
http://www.biomedcentral.com/1471-2180/5/35
Let me put it another way. Each time evolution finds another useful protein to add to a genome, there is an INCREASED tendency for it to be of a type that would add to that organisms ability to flexibly (ie intelligently) modulate its operations in response to its environment.
The final question is could they ever developed true intelligence if they did not have to compete with multicellular creatures that possessed a more efficient way of adding to that intelligence? I think that you may be right there but don’t be too confident about it.
It is very hard to see how nuclear weapons could exterminate all humanity. A much more realistic attempt could be promulgated via biological warfare.
Anthony:
This may be a quibble, but this particular example you mention is not pertinent. Multicellular organisms are known to have evolved independently many times. I remember reading about a count of 12 or 13 or so. And that includes only the ones with currently living descendants, of course. Others we would not know about, but surely there were many more.
LJK:
You may have misunderstood me, here. I did not mean to imply that we would just grab a broom, clean up, and go about building our spaceship, within a generation or two. My only point was that, no matter how bad the event, there would still be people around, and that eventually they would gain back what they lost, plus some. Space exploration would no longer be undertaken by our society, but by a different one that follows in our footsteps. Not overnight, of course, but chances are that things will go faster than the first time (on account of those footsteps). Even if it took 10,000 years to get back where we were, that would still allow for 100,000 repetitions in a billion years. This nuclear destruction would have to be unimaginably inevitable (99.999%) to keep us from eventually overcoming it. Apply this reasoning to any technological society in the galaxy, and you can see that it is not a very good explanation for why we are not the aliens.
I much appreciate your quote from one of my favorite movies, and of course I hope and believe that this scenario will not have to happen even once.
LJK:
Is this directed at anyone here? If so, please be more specific.
Ronald, at what point are you convinced that our economic wealth per person will stall forever. If your not, the factors you mentioned are purely delaying factors, and keep in mind they have to delay such potential until after starships become viable for them to work in favour of your argument.
Alternatively it may prove that humans have a powerful psychological link with planets, but it would have to be very strong indeed to make such real-estate so much more valuable that (O’Neil) colonies as to make it more economic to take a longer journey just for the privilege of sticking your feet on natural ground at the bottom of a deep gravitational well!
@ljk: “it also seems that many of those who deny the existence of extraterrestrials have agendas that are political and religious, not scientific”, etc.
Very well said, and how true!
With all due respect for people’s personal beliefs, and the meaning, purpose and morality they get out of those, I have often been amazed and puzzled in past years to observe how much easier many people find it to believe in all sorts of supernatural and (semi-, pseudo-, modern-) religious phenomena and interventions than in the relatively modest and scientifically supported possibility of extraterrestrial life.
Concretely: many of my friends and acquaintances believe in various gods, angels, demons, spirits, goblins, gnomes, elves, and whatever (and I will not even deny or discuss the theoretical possibility of some of them being right about some of it), but they will at the same time ridicule the possible existence of (any form of) extraterrestrial life, simply because it does not fit in with their views of a ‘unique’ (whatever that may mean) earth and human privileged position.
Likewise, and perhaps more crucially with a view to human survival, many if not most people will rather put their trust and hopes in a divine intervention than seriously consider our own possibilities and responsibilities with regard to long-term survival by interplanetary means, as so often discussed on this forum.
Concretely: many of my friends and acquaintances hope that God, Jesus, Yahweh, Allah, or any other divine being will save us in time from self-destruction, natural destruction or even major inconvenience from an impending energy crisis (and again I will not even question their hopes and beliefs here), but will at the same time strongly reject the whole idea of interplanetary colonization as a means of long-term survival, as being a waste of money and effort and even against the will of their deity.
It is, indeed, what people wish to believe and they will nearly always find confirmation of those beliefs, ignoring and ridiculing what is not in accordance with it.
This may indeed constitute a major obstacle to space-faring development and even a threat to human survival.
@ljk:
“LJK replies:
I want to add: If we cannot seem to get our acts together about a number of important matters, especially the technological and infrastructural ones regarding space exploration and colonization, while our civilization is in essentially running order, how do you expect it to happen when our society is taken down by nuclear war?”
Again, fully agree, however, I do notice a moral dilemma here: at the same time we acknowledge being an aggressive, destructive and possibly even self-destructive species, and yet we also wish to attempt to disperse our species, with all its inherent fallacies and risks, to other planetary systems for its survival.
One could also argue that we first have to get beyond certain civilizational childhood diseases *before* being ready and ‘worthy’ to go to the stars, to spread out life and civilization.
In other words, the urgency at the same time also poses the risk. Bluntly, like trying to flee from a centre of plague for survival, and in doing so spreading it.
ljk
Absolutely agree with your observations around the resistance to the very idea of advanced extraterrestrial civilisations, which do seem now to rest on a presumption that the probability of such a species emerging on a given planet is within an exceptionally narrow range just above zero. It could be so, be almost certainly isn’t.
Rob – As always a very interesting comment…yes, although I was thinking more about intelligence that could lead to something building spaceships, you are quite right about intelligence in the wider sense, although some microbes do seem to be very similar to extremely early forms and so such an apparent ‘trend’ may not have to occurr, statistically it will usually do so given the combination of random mutations, horizontal gener transfer and selection effects, along with beginning from a simple starting point. Eventually something will end up being fairly bright and able to use a screwdriver. The question is what is the variance in that timescale – don’t think we’ll get any further with that one, so I shall leave it at that for now.
Ronald
“spreading the plague” …That must be the “plague” that people who are not morally paralysed would call LIFE !
@Rob Henry: “Ronald, at what point (…) in favour of your argument.”
No, I do not argue that human wealth will stall in any foreseeable future (and if it did it would be equally detrimental for starship building).
What I meant is that, unless space colony building becomes spectacularly cheaper *in comparison with starship building* and/or other (potentially) inhabitable planetary systems will always be unreachable for us for technical reasons (propulsion etc.) and/or scientific reasons (scarcity etc.), planets are always *much* cheaper per unit area and unit time than space colonies.
Somewhat deficient comparison perhaps but just for illustration: it was much cheaper, per square mile or whatever, for early colonists to colonize the New World, than to build artificial colonies (platforms, rigs) in the ocean.
Eniac said on January 18, 2012 at 23:42:
[Quoting LJK] While there is of course the possibility that no alien life exists beyond our pale blue dot, it also seems that many of those who deny the existence of extraterrestrials have agendas that are political and religious, not scientific.
“Is this directed at anyone here? If so, please be more specific.”
LJK replies:
Hi Eniac – While I was making a general comment on this subject, I was “inspired” by spaceman’s post on January 15, 2012 at 1:20, to which I quote in part:
“I happened to be reading Paul Davies “The Eerie Silence” when this exciting result was announced last week. I wondered, based on what I had read in the book, what would the author’s opinion on the existence of so many planets the Milk Way. Interestingly, Davies did offer his opinion regarding the discovery to Popular Science:
“How much real estate is out there doesn’t matter,” he said. “My guess is there would be some hundreds of millions of Earth-like planets in the Milky Way, but that is no good to you if the probability of life forming on one of them is one in a trillion.”
http://www.popsci.com/science/article/2012-01/new-exoplanet-analysis-determines-planets-are-more-common-stars-milky-way
Translation: Davies says he doesn’t care how many stars and planets exist in the Milky Way and beyond, or if organic gunk covers the Universe – he still thinks (believes) that any life coming out of that is astronomically small. Only on Earth are we privileged so.
I can practically hear Davies about to give his reasons why we are the only living creatures in the entire Cosmos, and they have little to do with science.
I know we need actual evidence of extraterrestrial organisms to say with scientific honesty that there is other life in the Universe beyond Earth. But for people to say the odds of there being no such thing as an alien are high because they haven’t sent us a postcard or stopped by in person, or that our minimal explorations of the Sol system have turned up no obvious signs, is beyond annoying.
But far worse is when this denial comes from either fear or superstition based on the views of ancient people who had essentially no clue about science and even rejected it because such thinking did not jive with what their deities presumably told them (through their leaders, of course).
This is why I am more than a little suspicious of anyone who says there is no other life in existence. The scientific evidence we have so far, poor in certain respects as it is, says otherwise. Which means that there is probably an even better chance of alien life of all kinds in all sorts of places than we can barely imagine.
If it ends up that there is no life elsewhere, or that it is rare and remote, I will accept this if it is shown through science, not a feeling or because some self-elected authority figure says so. Same for the possibility of lots of alien beings out there.
And a big AMEN to those who just posted about how far too many people on this planet are willing to believe in ghosts, gods, spirits, goblins, the Loch Ness Monster, etc., but balk at ETI. What that says to me is that I think they are actually more fearful of the possibility of alien intelligences because there is a real chance of their actually existing.
And (n0) thanks to our popular media and general paranoia, many of these same humans think that ETI exist to conquer or destroy us and we will be powerless to stop them. On that very last point, that may be true. However, they should also take into consideration that the fact we have not been visited since the dawn of Earth 4.6 billion years ago – or at least if aliens did, it is not at all obvious – and have been seemingly left alone should show that the number of maurading alien species are quite small, or that they do not consider us worth the effort.
@Eniac: “Even if it took 10,000 years to get back where we were, (…). This nuclear destruction would have to be unimaginably inevitable (99.999%) to keep us from eventually overcoming it”.
Or very frequent, repetitive self-destruction then being an inevitable characteristic of all civilizations.
But I doubt that, since even our agressive and violent human civilization has been existing and developing more or less continuously (when considered at a global level) for at least 6000 years, and, despite the rantings of doom-and-gloom-prophets, our options and possibilities are now greater than ever.
And with you I doubt this as an explanation for the Fermi Paradox.
A still firmly believe that the most logical and likely explanation for Fermi is also the most mundane one: the number of contemporary technological civilizations in our MW galaxy is probably extremely small, if not 1.
The present microlensing results are an encouraging confirmation of the (higher range of the) Kepler and HARPS results, but I do not think that they change the outlook for habitable planets so dramatically, the more optimistic (and more recent) extrapolations from HARPS and Kepler gave somewhat similar results. Ok, the present results are even a bit more encouraging with regard to overall planetary abundance, but smaller, earthlike (up to 5 Me) planets are not part of this survey.
What really matters when it comes to number of habitable planets is the combination (overlap) of earthlike planets and Habitable Zone (HZ).
Jorgensen’s conclusion “10 billion with planets in the habitable zone” is not in the paper itself. And a planet in the HZ is not yet the same as an earthlike planet in the HZ. This precentage may be significantly lower than the optimistic 10% mentioned here, maybe only 1-2%.
Furthermore, I think it is not right to extrapolate the planetary data for (a part of) the galactic disk to the entire MW, while it is known that the halo and many if not most of the thick disk stars are rather unsuitable for planets (old, very low-metallicity, red dwarfs).
If we limit ourselves more modestly to the thin and intermediate disk, even considering most of that Galactic HZ, and to more or less stable (quiet), more or less solar type stars, and then consider the more or less earth-sized planets in the HZ, the rough estimates or guesstimates of number of (potentially) habitable earthlike planets in our MW galaxy vary from (several) tens of millions to a few hundred million.
See our thread:
https://centauri-dreams.org/?p=11625&cpage=1#comments
This new survey would rather put that guesstimate toward the higher end of that range, several hundred million.
This may seem like a lot as a breeding ground for life and indeed it is, however, as an input for the Drake equation (starting there at the fraction of inhabitable planets, Ne), with all the following obstacles to overcome, the end-resulting number of high-tech civilizations is still disappointingly low.
Ronald said on January 19, 2012 at 5:48:
[Quoting LJK] I want to add: If we cannot seem to get our acts together about a number of important matters, especially the technological and infrastructural ones regarding space exploration and colonization, while our civilization is in essentially running order, how do you expect it to happen when our society is taken down by nuclear war?”
Again, fully agree, however, I do notice a moral dilemma here: at the same time we acknowledge being an aggressive, destructive and possibly even self-destructive species, and yet we also wish to attempt to disperse our species, with all its inherent fallacies and risks, to other planetary systems for its survival.
LJK replies:
I have batted that issue around for a while now. My conclusion is that if we wait for humanity to become a bunch of saints, we will never get anywhere literally and culturally. In fact, if we do wait and try to become pure, enlightened beings, we may actually lose our drive to explore and expand. In either case, we would lose what makes us human, which if you really think about it is no better or worse than any other creature on Earth. Do we condemn sharks or tigers for being predators, or do we accept them as part of nature? We are more animals of nature than we think we are, we just get distracted by all the shiny toys and presumably lofty thoughts we have.
Think where we would not be if we waited for us to “improve” ourselves – whatever that really means. I suppose we could all become saints of the Christian style, for example, but then can we also keep those traits which allow us to build and think independently? I do not like suffering and ignorance any more than any other decent human being, but how realistic is it to assume and hope that we can and have to make the lives of every person on Earth better before we can move on to such things as space?
We are a species of over 7 billion individuals now comprising a broad technological civilization that remains almost exclusively on one finite planet (I barely count those few folks aboard the ISS, as they are still very dependent and connected to the rest of humanity in all the fundamental ways). Anyone here think we can remain this way and keep behaving and expanding as we do without consequences?
I know space colonization will not solve the population problem any time soon, but it does provide one solution out of several that could keep us from either stagnating or going outright extinct. But we need to act SOON, not when we all get “better”. While I know that utilizing space is not easy, at least it is doable and I provide a concrete solution here, whereas the comment that we need to solve all our problem first before moving on is both vague and one with too many conflicting suggestions from many sources, most of whom conflict with one another.
It is just a shame that the idea of exploring and colonizing space is seen as old-fashioned and irrelevant by many in today’s world, because it really just shows how far we have not progressed in many important, fundamental ways.
To add a few more points regarding whether we humans are “good” enough to expand into the galaxy or not:
1. The Universe is freaking huge. Heck, the Milky Way galaxy alone is vast enough for a species that you cannot even collectively see once one gets just a few hundred miles away from Earth. Do you really think we could wreck much of anything out there even if we did decide to go on a celestial rampage? Again, we as a species are still thinking much too provincially. Everyone really needs to see the Eames’ short film Powers of Ten multiple times to let it sink in.
The Universe overall has survived countless impacts, supernovae, black holes, gamma ray bursts, and galactic collisions over its 13.7 billion year history. All our nuclear weapons from the height of the Cold War detonated together would barely make a localized blip on the cosmic scale. And we think a little trash and vandalism is going to phase the Cosmos? Besides, the very nature of space and other worlds in our Sol system alone preclude much “screwing around” unless such humans want to die harshly from their poor actions in short order.
And if there do happen to be any ETI sophisticated enough to be concerned about our juvenile behavior ala The Day the Earth Stood Still (the original 1951 film version, not the crappy recent remake), such beings would probably also have the means to take us down before we could soil the galaxy as it were. The fact that no one has yet landed their spaceship in Washington, D.C. to tell us to grow up or else is telling in several ways.
2. What exactly constitutes “good” behavior in a cosmic context? Think of the fictional Borg from Star Trek: They looked upon their assimilation of other species as a good thing both for them and their subjects. In our reality, missionaries (in the past especially) felt it was their divine duty to save the souls of cultures they considered less fortunate, regardless of what the natives really thought on the matter.
If advanced ETI do exist and can explore the galaxy and beyond, what are the odds that they will be anything like our intrepid crew of the Starship Enterprise from Star Trek, who tried to live by the Prime Directive – but often broke that rule whenever they felt it was in the best interest of the less sophisticated species.
My take on what will happen when we do go into the Final Frontier – and what has probably already happened countless times across the Universe since the first life forms pulled themselves out of the muck or whatever they evolved in:
We are going to encounter beings very much unlike us, so much so that in some cases neither party will recognize the other as intelligent or even living creatures as they define life. There will be misunderstandings and conflicts. Sometimes we will get lucky and the two species will be able to at least recognize enough not to inadvertently or deliberately crush the other. We may even learn something valuable between ourselves, though any actual help or salvation will probably come about indirectly if at all.
I am iffy about any kind of galactic federation or empire, however, especially if the parties involved are still organic.
Take what I said above about how harsh the natural Universe has been since the Big Bang (or Big Bounce or whatever) and apply it to all the little creatures dwelling around and inbetween all those stars in the sky. The conclusion is that the Cosmos has always been a kind of mess guided by physical laws and always will be, and the same will go for all the life forms in it, intelligent and otherwise.
So stop fretting about whether we are “good” enough for the rest of the Universe. Such things matter little when you’ve got 100 billion galaxies across 13.7 billion light years, and those numbers may be conservative.
Thanks Ronald for that elaboration. I can now see the logic behind your thinking.
I still feel that I should point out that that each extraterrestrial Sol based colony on its own does not have to be self-supporting, and that in itself may lower cost. Also I can’t help but think that the cost of transporting a colony to a new star system would, in most schemes, be many times higher than the cost of building the same endpoint colony within our own system, but on an O’Neil habitat.
Half the posters here seem to have taken a strange religious turn, so I thought I should also have a go. To me a current danger that poses a threat to the health of humanity is the paradigm approach to science. Let me explain.
To me science has never been its models, but the predictive power that flows from those models. The latter has a large and quantifiable benefit to humanity, but a religious type adherence to these models that lie behind science just interferes with the process of advancement and the delivery of even greater benefits.
This leads me to the problem of abiogenesis. It doesn’t take a religious nutter to notice that every single life form on Earth is incredibly complex, and that much of the information in that complexity is conserved across all life, or that even designing any self replicating machine seems to be currently beyond us. This idea that life develops everywhere that there is water and carbon compounds is driven by the Urey-Miller experiment and was established at a time when life was thought to be simple. However balance of evidence since then has been against it, though never strong enough to overturn anything that looked like a paradigm of science.
Ljk is correct that evidence of life’s early appearance on Earth hints that fl is not too low, even though that conclusion relies on abiogenesis not requiring temporary high energy conditions that may only ever exist early in a planets history. However he is completely wrong in assuming fl = 1 in a trillion range would be unscientifically low, unless he is aware of evidence that firmly places the minimum complexity for life at much lower than that of any form that we know of on Earth.
My plea is that we all give up theses stifling paradigms, especially when the evidence supporting them is minimal, and re-evaluate our stance each time new evidence comes to hand. We should replace that reverence with the sole interest of maximising sciences predictive power. To me, it is science at its best to discuss and debate the models, but science at its worst to actually believe.
@LJK
What scientific evidence? So far, there is zero evidence of other life. Nilch. Not a shred. And not for lack of searching. Davies is right: Discovering places where life could exist does not say anything about how likely it is to be there. A single factor in the Drake equation can easily ruin it all, and I am with Rob Henry on which one that is.
And then there is the obvious problem that you also mention, that we have not been visited by aliens (in which case we most likely would BE aliens). It is a real problem, because it puts us in the uncomfortable position to suppose either of three things: 1) We, and everybody else, will fail to settle the galaxy, 2) we will be unique in being the first ones to do so, or 3) someone has done so and we haven’t noticed.
I suppose you are a proponent of 3), but I am not clear how you explain that our system/planet somehow got missed in the process. Someone decreeing odd-numbered stars are not to be settled? Blue planets with lifeforms on them off-limits? decreed by whom? Enforced how exactly over billions of years, without fail?
You correctly point out the vastness of the universe, but you neglect to acknowledge that this vastness is more than matched by the vastness of time combined with exponential growth. If Sol is not reached in a million years, it will surely be found in the next million, unless we are dealing with exceptionally sluggish intelligent lifeforms here.
Of course, there is always: 4) abiogenesis is so unlikely as to make us truly alone in the galaxy. I understand your displeasure with such a proposition, but it is the least religious, the one least driven by wishful thinking. It avoids the doom and gloom of 1), the non-Copernicanity of 2), and the implausibility of 3).
Any Exoplanet Possible in a ‘Compulsive’ Universe Analysis
by Ray Villard
Wed Jan 18, 2012 12:29 PM ET
The astronomy news last week saw a big bang in the search for planets outside of our solar system.
The cumulative discoveries reported at the meeting of the American Astronomical Society have taken us higher toward the intellectual summit of thousands of years of speculation as to whether Earth is alone in the universe.
We will ultimately reach that summit with the eventual discovery that life is a condition of the universe. In other words, that self-replicating matter is nature’s favorite form of self-expression.
Gravitational microlensing surveys have lead us to the conclusion that there are zillions of places for life out there. Planets are everywhere in the universe. They outnumber the stars in our Milky Way galaxy.
The estimate of over 100 billion worlds in the galaxy reported last week leapfrogs ahead of the Kepler space telescope’s meticulous star-by-star planet inventory, which at present exceeds 2,300 “candidate” exoplanets and an estimate of 50 billion alien worlds.
As the first dedicated exoplanet space missions to seek out Earth-sized planets in stellar habitable zones, Kepler’s ongoing discoveries have “overwhelmed the astronomy community” says John Johnson of Caltech
Full article here:
http://news.discovery.com/space/exoplanet-harvest-shows-that-we-live-in-a-compulsive-universe-120118.html
To quote:
Still, like the old Chamberlin-Moulton theory of planet formation, there will hardcore skeptics dismissing the possibility of extraterrestrial life, even in light of our planet bonanza.
But anything is possible in a compulsive universe.
The only serious atempt to explain how life got stated (and could get started anywhere) ,comes from a branch of information theory . This theory is far from generally axcepted , but there is a number of gifted peoble working on it . It postulates that in the border area betwen Chaos and organisation exists a “fertile” mixture where a separate law of nature comes into existence , the law of self-organisation . This law of nature has never been stated in a comlete , general way , but a few specifik substatements has been attempted by various branches of science , which has stumbled upon a specifik manifstation of it .
For som odd reason very few people seems to be curious about how a genaral statement of this law might look . Pehabs its because the whole thing smells a little bit of religion…
@ljk, with regard to your two long comments regarding our ‘worthiness’ to colonize the cosmos ( January 19, 2012 at 13:42, 14:20):
You totally convinced me (as far as that was still needed) and I fully agree with everything you say: yes, we are not particularly bad in a moral sense, just human. And that aggressive drive may also be exactly what will take us to the stars. And yes, we cannot wait until we are perfect whatever that may mean anyway, in that case we’ll probably have to wait forever and be too late for anything. And finally, yes, the universe, even the observable part of it, is a unimaginably huge place, and there is definitely plenty of space for us! In fact, the real challenge for us humans in the foreseeable future will not be to be careful enough with the universe while colonizing it, but rather how to colonize it fast enough.
Eniac said on January 19, 2012 at 22:53:
[Quoting LJK] The scientific evidence we have so far, poor in certain respects as it is, says otherwise. Which means that there is probably an even better chance of alien life of all kinds in all sorts of places than we can barely imagine.
“What scientific evidence? So far, there is zero evidence of other life. Nilch. Not a shred. And not for lack of searching. Davies is right: Discovering places where life could exist does not say anything about how likely it is to be there. A single factor in the Drake equation can easily ruin it all, and I am with Rob Henry on which one that is.”
LJK replies:
I was not referring to finding actual extraterrestrial life (I would have been shouting this from the rooftops if I had such news). I was actually referring to the “smoking guns” science has found so far, which I have said several times before in this thread and did not want to become repetitive, but will here now clarity:
The many complex organic molecules found throughout the Universe from meteorites to distant galaxies, the worlds in our Sol system which once seemed inhospitable mainly because they were not like Earth but now appear at least friendly to simple life forms (this list even includes places like Venus and Io), the life forms found on Earth that dwell almost everywhere, including and especially in places we once thought hostile to any kind of organisms (hydrothermal vents, natural boiling acidic pools, nuclear reactor plant pools, miles under solid rock, and some even when exposed directly to space via experiments), and the evidence for thousands of exoplanets in the rather small sampling we have conducted, which translates into more planets than stars in the Milky Way galaxy, and by extrapolation, to probably every one of the estimated 100 billion galaxies in the known Universe.
I recognize that all this evidence still does not mean there is alien life until we actually have solid, scientific proof of it one way or the other (and not anecdotes or wishful thinking), but only the most virulent anti-extraterrestrial life opponent would declare that our Universe is not at least suitable for the existence of living creatures beyond Earth.
Even the Rare Earthers Ward and Brownlee agree that many exoworlds likely have at least bountiful amounts of simple organisms on them, based in part on how quickly life began in our planet’s early history just after it cooled down from a molten state.
Eniac then says:
“And then there is the obvious problem that you also mention, that we have not been visited by aliens (in which case we most likely would BE aliens). It is a real problem, because it puts us in the uncomfortable position to suppose either of three things: 1) We, and everybody else, will fail to settle the galaxy, 2) we will be unique in being the first ones to do so, or 3) someone has done so and we haven’t noticed.
“I suppose you are a proponent of 3), but I am not clear how you explain that our system/planet somehow got missed in the process. Someone decreeing odd-numbered stars are not to be settled? Blue planets with life forms on them off-limits? decreed by whom? Enforced how exactly over billions of years, without fail?”
LJK replies:
Obviously just about anything I say here will be an educated guess, but I can say one thing with a fair degree of certainty: If ETI ever were or are here now, it is not terribly obvious, at least to me – though I once had a UFO proponent tell me there is an entire alien civilization that has been living below the surface of our planet for centuries secretly manipulating human affairs, so ya never know.
Eniac, you assume the following aspects about ETI: That they want or need to colonize the galaxy (assuming they are even able to achieve interstellar travel), that an alien species would find a planet alien to them such as Earth appealing or even livable/useful, and that colonizing the 400 billion star systems in the Milky Way is something that can be done in a relatively straightforward manner running on a consistent schedule.
All of your presumptions indicate that an alien species evolved in an alien environment on an alien world (or an interstellar nebulae or inside a sun, for the sake of removing the paradigm that all life has to come from a planet or other kind of solid world), will behave much as we humans do and intend to when it comes to the rest of the galaxy.
While not impossible, I take from the lack of scientific evidence that we have or are being visited by ETI, along with our lack of evidence for any obvious signals from or signs of them in the Universe, that – discounting the possibility of no one out there for the moment – alien beings are going to have an alien mindset and physiology, meaning they won’t be like most of the much too humanoid creatures on Star Trek.
Colonizing a whole galaxy may just be a lot of expensive and time-consuming work, or it may be plainly unnecessary to another species. For all we know, leaving their home world might be an act some beings would never even consider or could even be against their religion. We have plenty of examples of those attitudes right here on this planet.
And just as we know we likely will not find another planet that duplicates Earth to the point we could walk and live upon it either unaided or without having to modify it, the odds are pretty good that our planet will not be suitable to an alien species without requiring some kind of adaptation or change. So far I do not see any evidence that ETI are modifying Earth to their needs – but ya never know with this global warming thing going on and those folks who so strongly oppose the very concept despite all the scientific evidence for its existence. Just sayin’.
Eniac says next:
“You correctly point out the vastness of the universe, but you neglect to acknowledge that this vastness is more than matched by the vastness of time combined with exponential growth. If Sol is not reached in a million years, it will surely be found in the next million, unless we are dealing with exceptionally sluggish intelligent life forms here.”
LJK replies:
See what I just wrote above. Things can change so rapidly in a few thousand years, let alone one million, that I can see just about any colonization effort, including and especially our own, go down numerous and various paths differing from the original plans, a number of which could end with some members of the species refusing to colonize any further, running into other civilizations that do not want the intrusion, or just ending up extinct. And I will say one more time, just because we find Earth so homey does not mean an alien species from an alien world will feel the same.
Now I have been primarily referring to organic beings here, ones who can build and manipulate some form of relevant technology. If our ETI are Artilects or some kind of being wildly different from what we can imagine (and I think our imaginations are pretty limited in this area due to our lack of cosmic experience), then talking about galactic colonization may be downright naïve.
Just for the record, I think and hope we will find out if we are alone or not long before 1 Million CE, but I also think that if ETI were coming our way it would have happened long before now. We humans may have to finally accept that we are not the most important or interesting things in the Cosmos, even if the whole place is devoid of life beyond Earth.
Eniac finally says:
“Of course, there is always: 4) abiogenesis is so unlikely as to make us truly alone in the galaxy. I understand your displeasure with such a proposition, but it is the least religious, the one least driven by wishful thinking. It avoids the doom and gloom of 1), the non-Copernicanity of 2), and the implausibility of 3).”
LJK replies:
Again, while I recognize that statistically Earth might be the only planet with life in at least this galaxy (and we could get into what exactly constitutes a living organism, but not here), the scientific evidence I have cited above which at the very least shows that not every corner of the Cosmos is hostile to the possibility for our kind of life says to me beyond mere hope that something besides dust and gas, glaring suns, and icy/rocky/gassy worlds exist in our reality. Now let’s go look for ‘em!
Ole Burde, that *border of Chaos* school of thought on life’s origin was proceeded by at least two other, with which it still competes.
1) There just so happen to be matter organizing forces in this universe that might not be directly apparent from the laws of physics. This *dialectic materialism* school of thought was assumed true by some Marxists at a time when chemists were noting the great difficulty of synthesising organic matter from inorganic. In that context, it got a huge boost from the Urey-Miller experiment when it was found that their simulated early Earth environment produced not just organics, but some amino acids that were essential to life. Further experiments followed with some limited success. Under these precepts life will appear everywhere water is found in combination with a past atmosphere and organics, so at least it is easy to test for.
2) The idea that if we studied the main features of self-replicating machines in general, and life on Earth in particular we could demise how life could have started. This *top down* school of thought suffered one great problem. The more we investigated this method of study, the more unlikely life seemed, perhaps even putting fl at millions of orders of magnitude to one against. Many contributed to this completely logical and unbiased approach, but its greatest exponent so far has been Manfried Eigen. He showed that under highly unusual and narrow conditions a high information content self-replicating cycle that avoided rapid dive into *error catastrophe* was possible. This *hypercycle* idea allows us to raise the prospects of life’s origin to the range of a few hundreds of orders of magnitude to one against, and it is possible that further work will bring it down more.
That work that you mentioned would be something like a hybrid of those two approaches. Note that they seem to have nothing as yet but a feeling that this might work – but we would be wise to keep them in mind on the off chance.
Of cause Ole, the most scientific approach of all is to go forth and seek out instances of life’s origin that are independent of our own, but until then we may have to over-rely on theory.
@LJK: First of all, I completely agree with you on many things. We have ample proof that there is plenty of opportunity for life to thrive in the universe. The universe does not care about us, and we should not wait to get out there until we are “good” whatever that may mean. Also, that if there ever were ETI visiting us, they would have been here before us, already.
Where we disagree is in how likely it is that at least some of the ETI out there would want to at least occasionally colonize another star system. You say I make assumptions about ETI, but I am actually very careful about the assumptions I am making. I make only a single assumption: That at least one of those ETI are of a nature where they, at least occasionally, would colonize another star system. This one assumption has the inevitable consequence that the galaxy will soon be filled with the descendents of this ETI.
If on average, a successful colonization happens every 10,000 years, expansion will take place at ~1 parsec/10,000 years. This has been said often enough that I do not have to elaborate here, you can calculate yourself the time it takes to fill the galaxy. I would be curious what you think could possibly stop such an expansion, or keep it from eventually reaching all star systems. You say:
I completely agree that there will be no long term effort, and also that there will be some members of the species refusing to colonize any further. Heck, most will probably do so. However, what you are assuming is that ALL members of the species will refuse to colonize further, FOREVER. Big difference.
Lastly, the myth about life arising on Earth as soon as it stopped glowing hot. First of all, any fossil evidence of microbic life is inherently not incontrovertible. Even if you believe all of it, there is still room for almost a billion years of no life. Second, It is a given that life started on Earth sometime between then and now, and there is nothing portentive about this being earlier rather than later. This argument is just one step removed from saying our own existence is proof of that of others, which is deeply flawed, statistically.
@Rob:
Rob, I think you hit the nail on the head, here, and it goes a long way to explain how the spontaneous generation of life is even possible at all. Eigen has done some of the most important work in this field, but appears to be not terribly well known today, despite the Nobel prize.
In my view, it is likely that the universe is just big enough and has enough planets to bridge the remaining gap of “a few hundreds of orders of magnitude to one against”. Or maybe that would be a stretch?. Let’s be optimistic, and say: A few tens of orders of magnitude.
The work by Eigen is exactly one of the specifik cases where self-organisation has been investigated that I mentioned earlier .
So, the “hypercykle” is ” posible” … Is that all ?
It seems to me unavoidable to reach the conclution that such behaviors of complex systems are more than just possible , they HAVE to happen , and that implies a DIRECTION of behaviour inherent under some conditions to what we normally would consider as blind luck .
We could wait a hundred years for a genious to be born , who could se clearly what hides behind the “metrix” of statistical reality , or we could just chip away at it by trial and error , and uman curiosity.
Ole, I’m sorry that I did not give my objection to the certainty implied in your earlier comment, but here goes.
For a while there was a tendency to take life as the forced outcome of the natural trends of *chemical evolution*. As this began to fail experimentally, it hit another: that evolution before self-replication was against the very principles Darwin’s stood for. So to recover the idea that life could be the forced outcome of certain conditions we must start with non-trivial self-replication (as defined by von Neumann).
Later it was shown that any far from equilibrium chemical environment that was sufficiently complex would almost certainly contain pathways that, if isolated from others, would be self-replicating. Now it was imagined by some that the hitherto carefully studied problem of self-replication could be sidelined, but this was all at the expense of a completely new problem that looked even more difficult to crack called *autonomy* (roughly speaking, the isolation of that self replicating path from its environment, and the prevention of too much energy being drained by unwanted side reactions, for one cycle to be able to self-reinforce).
One day the problem of autonomy might be solved by the groups you speak of, but that will only take them to the threshold of the trivial v non-trivial replication problem. It has been said that it may be possible to progress further by allowing a *metabolic genome*, However, for evolution to lead to improvement some rigorous conditions have to be met. It is very challenging to find conditions that meet this with that sort of genome.
Note how that approach now looks like wishful thinking. Note how a new theoretical or experimental result could change such a view, but I just believe that it is wrong to think that way ahead of any evidence, especially in a day an age where we can no longer work from a starting point that assumes that morphologically simple modern forms are also biochemically simple.
Oops, I forgot to add, that the reason I did not place Eigen in the same group, is that he kept his game eye on the central problem. Many others seem to have lost the ball altogether. I think that similarity of their use of spontaneous appearance of additional order is coincidental due to their subject matter, but now that you mention it, I really should look into it.
Eniac said on January 21, 2012 at 9:47:
“@LJK: First of all, I completely agree with you on many things. We have ample proof that there is plenty of opportunity for life to thrive in the universe. The universe does not care about us, and we should not wait to get out there until we are “good” whatever that may mean. Also, that if there ever were ETI visiting us, they would have been here before us, already.”
LJK replies:
Eniac, I want you to know that my thoughts are similar in regards to much of what you say. I am not trying to disagree with you just for the sake of doing it, but only if I too feel strongly on certain matters. I freely admit I could be wrong and have no problem learning what the truth is some day – unless somebody shows that humans are the best that the Universe can ever do. That prospect and its implications are much too frightening to comprehend. :^)
Eniac says:
“I completely agree that there will be no long term effort, and also that there will be some members of the species refusing to colonize any further. Heck, most will probably do so. However, what you are assuming is that ALL members of the species will refuse to colonize further, FOREVER. Big difference.”
LJK replies:
I agree that, in principle, all it takes is just one species with the will and ability to colonize the galaxy can make all the difference. The fact that their presence on this planet is not obvious leads me to the conclusion that – if we set aside for the moment that no one else with such a cosmic drive and ability exists – in order of importance:
They did stop at Earth, but given the ten billion year history of the galaxy and the 4.6 billion year existence of our planet, it happened a very long time ago if you factor in the statistic odds of when an ETI might ever visit, thus they either deliberately left no evidence of their presence or it is long destroyed or buried by our planet’s ever changing environment.
Factor in the likelihood that if even if an archaeologist or paleontologist ever found an alien artifact, the chances are quite good that it would not be recognized for what it is, or they would figure out it is not from this planet but be too afraid to tell their peers, or if they did tell their colleagues they would be beaten down socially until they repented of their sin of daring to say that the emperor has no clothes, or removed altogether.
And I want to say again it is possible that an alien species that evolved on an alien world might not find Earth appealing, or that if they were nomadic like a less harsh version of the aliens in Independence Day they might find it easier to utilize the resources from our comets, planetoids, and moons in our Sol system rather than dig from a deep gravity well like Earth. Thus we should be on the alert for mining scars and leftover equipment as we explore the planetoid and comet belts. Then again, what would the Dawn team do if they found artificial scratches on Ceres? Would they jump for joy or dismiss them just as scientists have been dismissing the growing evidence that Mars once had life and may still do?
Eniac says:
“Lastly, the myth about life arising on Earth as soon as it stopped glowing hot. First of all, any fossil evidence of microbic life is inherently not incontrovertible. Even if you believe all of it, there is still room for almost a billion years of no life. Second, It is a given that life started on Earth sometime between then and now, and there is nothing portentive about this being earlier rather than later. This argument is just one step removed from saying our own existence is proof of that of others, which is deeply flawed, statistically.”
LJK replies:
The earliest evidence for life on Earth for which scientists are in general agreement upon was already fairly well along developmentally for single-celled creatures. Unless we are missing something key about evolution, or unless these microbes were planted on our world from somewhere else, there has to have been an earlier and even simpler set of organisms arising between 4.6 and 3.5 billion years ago. Granted this does not mean they showed up one week after cooled off, but that is still pretty darn early and keep in mind that these creatures had to survive Earth’s heavy bombardment phase.
While we can continue to debate whether the obvious existence of terrestrial life along with all the smoking guns we have found so far means that other beings must exist in the Cosmos, Earth life at least shows it can happen in this Universe. Whether it happens a little or a lot is the question we all want the answer to.
I feel the same way, except I do not see the prospect of “humans being the best the universe can do” as quite so gloomy. It has its upsides :)
When you talk about the aliens having “stopped” at Earth, I feel again the need to stress that in my opinion there is no way that anyone will come this far and not intend to stay. Whatever their needs are, our solar system almost certainly fulfills their requirements for usable real estate, precisely because it is not that special and much like any other. If they like rocky planets, we have that. If they like gas giants, we have that. If they like asteroids, we have that. Sunlit empty space to park their O’Neill RVs, solar corona for plasma-beings, you name it. The principal reason they would come is that the real estate is unoccupied. With enough time, such unoccupied space is bound to become rare and precious in the galaxy.
I do not believe it is likely that any space-faring civilization will ever die out without leaving viable descendants behind. In our experience, life is forever. The one example we know of lasted for billions of years, on just one single planet. If they do somehow do themselves in, plus their crops, pets, head lice and gut fauna, the system will become unoccupied. Fair game for the inhabitants of the many neighboring systems to recolonize.
Thus, we should be seeing not only artifacts, but also the living descendants of the ETI themselves. In particular the descendants, because they would be around much longer and be much better preserved than mere artifacts. As I like to say: We would be them. Genetic evidence shows conclusively that we are not. We can trace our heritage to the simplest of organisms, billions of years ago and certainly not intelligent.
I suppose there is a chance that they are here and we don’t know: in the ocean below the surface of some moon, the atmosphere of a gas giant, the solar corona, or somewhere we are not thinking of. The chance of that being the case is decreasing steadily, though, as we intensify our exploration of the solar system without finding signs of life.
I am with you in hoping that we will, some day, for the sheer thrill of the scientific bounty that would come with an independently evolved biology. Sadly, though, I do not share your confidence.
Far more likely than some missing key about evolution or planted microbes would be that the “general agreement” is driven by much wishful thinking and the “microbes” are actually bubbles or some other feature shaped by unknown inorganic processes that can be found to look like cells after you scan past enough of them that don’t. We have seen this happen with the Martian microbes, where the general agreement pretty much went away after the results became the subject of wider discussion. I do not think these fossil ones are any better, just more obscure. I looked at one paper once and was not terribly convinced.
And again, even as you believe all of the claims: We know life had to start at some time in the past, because it is here, now. Why not in the earliest 10% of the time? That is actually more plausible, because it leaves more time for evolution. All these observations are based on a fixed posterior, they tell us nothing about the prior probability. The argument of the early rise of life is a statistical fallacy, nothing more.
A discovery of independent life would go far to clear this issue up. As long as that doesn’t happen, the absence of starfaring ETI is the best evidence we have for the probability estimate we seek.
Eniac said on January 23, 2012 at 17:46:
“When you talk about the aliens having “stopped” at Earth, I feel again the need to stress that in my opinion there is no way that anyone will come this far and not intend to stay. Whatever their needs are, our solar system almost certainly fulfills their requirements for usable real estate, precisely because it is not that special and much like any other.”
This may be just my personal preference, but I have to wonder if you do have some kind of alien version of a Worldship with beings who have spent their whole lives in space, perhaps they do not want to live on a planet. Instead solar systems are for studying and gathering resources, then moving on to the next system to see what the galaxy has to offer.
As for the averageness of our Sol system, so far we have found very few systems that even come close to resembling ours. I know we are just scraping the tip of the celestial iceberg, but so far several thousand finds have left us with more gas giants circling very close to their suns than ones resembling our neighborhood.
Wow Eniac, your disavowing of the consensus of modern microfossil interpretation has really put the cat among the pidgins. Sure, its early history is littered with false positives, but they have supposedly put that all behind them. I have been highly impressed how the modern, and (to an outsider) subjective interpretations of these microfossils are now so accurate, that they seem to be able to follow some bacterial genera over hundreds of millions of years, and show when they are replaced by new groups.
What I’m saying is either the quality of these earlier fossils is incredibly low (I know that it is at least a little lower than is typical) or your meagre sounding objection has far greater implications for this field than you imply.
There exists another possiblity for the origin of life on earth than those disgussed here . Life on earth might be the result of some other intelligent species having tryed to SEED a big number of stars with their own onecelled lifeforms .
The reasons for doing this could have been similar to our own plans to terraforming in order to make a human setlement possible , or they could be
relious in nature ,or something we cant classify .
This theory has the advantage of being capable of explaining why life seems to have emerged in forms that were almost as compleks as todays.
It also has the advantage of having a good chance of eventualy being verifyed OR made unlikely . If extraterrestrial lifeforms on a large number of planets were found to have the same basic DNA structures as on earth , then it would be simlest explanation .
Ole Burde said on January 24, 2012 at 12:15:
“There exists another possiblity for the origin of life on earth than those disgussed here . Life on earth might be the result of some other intelligent species having tryed to SEED a big number of stars with their own onecelled lifeforms.”
LJK replies:
I did mention this possibility in an earlier post. The late Francis Crick of DNA helix fame was an advocate of directed panspermia and even co-wrote a paper and a whole book about it titled Life Itself:
http://www.astrobio.net/index.php?option=com_retrospection&task=detail&id=1107
Ole said:
“The reasons for doing this could have been similar to our own plans to terraforming in order to make a human setlement possible , or they could be
relious in nature ,or something we cant classify.”
LJK replies:
The key aspects of successful life forms which I bet are true for all organisms throughout the Universe no matter how simple, complex, or just plain strange they are is the following: Survival, reproduction, and spreading out into new territory to continually repeat the first two items.
Ole then said:
“This theory has the advantage of being capable of explaining why life seems to have emerged in forms that were almost as compleks as todays.”
LJK replies:
Although the simpler explanation is that it is rather tough to find very tiny creatures that had neither bones nor hard shells to fossilize and existed billions of years ago on a very active planet like Earth. I also appreciate the fact that the directed panspermia theory is much more exciting in one sense – though you might also think that life just appearing anywhere would be exciting enough.
My one issue with the deliberate placing of life on our world from elsewhere is that it reminds me of the thinking that our ancestors were incapable of making impressive structures on their own, that they had to have help from ETI. Such thinking shows a lack of knowledge and appreciation for what our ancient relatives could accomplish with their own brains and hands. It also adds levels of complexity that make the possibility weaker along with failing to answer the key question of where did it all come from in the first place?
Ole said:
“It also has the advantage of having a good chance of eventualy being verifyed OR made unlikely . If extraterrestrial lifeforms on a large number of planets were found to have the same basic DNA structures as on earth , then it would be simlest explanation.”
Which is why we so badly need to get out there and find some actual alien life, be it on Mars or Zeta Reticuli. Yikes – What if Star Trek turns out to be right about life being planted all over the galaxy on purpose!
Good thought. But in my mind, if the trip takes hundreds or thousands of years, there is no harm in staying a little while where it is warm and interesting. Also, it has probably become awfully tight and stuffy aboard the ship, better to stay around long enough to build a replacement, and a few more while we are at it. After all, isn’t it all about going forth and multiplying? And then, when it is time to leave, do we really have to gather together everybody? Some may want to hang out a bit longer. So much to see, so much to do.
Do we have you arguing Rare Earth, now? :-) Yes, of course, we have mostly found such planets as we can easily detect. Close-in Jupiters, galore. Last I heard, we would not be able to see a single planet in our own system if it were a nearby star. I believe the original topic of this thread is of interest here.
If organic beings, whether it be us or someone else, ever do build a Worldship, such a ship will purposely be roomy and even luxurious. See the Ultimate Project design for one example that would carry one million humans to the nearest Earthlike exoplanets – it is pretty roomy:
https://centauri-dreams.org/?p=1930
There is something else to consider which a lot of the old school science fiction writers failed to postulate upon such multigenerational starships, due to the eras in which they wrote about such vessels: The possibility for the crew to pass their time immersed in virtual reality. If you can spend much of your life in an ideal setting that seems real, you may not worry about being “stuck” on a ship in deep space or care if it is roomy or not.
Of course if you can live in a happy world inside your mind, would you even want to bother leaving home? And if you still decide to take that interstellar trip and are among the final generation that reaches your celestial destination, would you want to leave your artificial utopia for a comparatively dirty, smelly planet and have to deal with the pain and mundanities of everyday, ordinary life?
This is why I increasingly think that humans are the weakest link when it comes to the realities of interstellar travel and exploration.
As for the kinds and types of exoworlds out there, if the majority of them are those super Jovians which almost hug their parent suns as seems to be the case, we will have to reevaluate what kinds of life might exist on those worlds and just how much could there actually be as a result. Add in the theory that these monster planets migrated in from the outer regions of their solar systems – probably dislodging and disrupting their smaller neighbors along the way – and we may have even fewer habitable Earthlike planets than we imagine.
I know it is difficult for us to find the Earth-sized worlds with our current limited methods of detection, but the fact that the majority of the solar systems we have found so far since 1992 do not resemble ours really needs to be more of a wakeup call regarding alien life than I sometimes think it is. We keep looking and hoping for a twin of our planet when the Universe seems to keep shouting at us to change our paradigms.
I too think that there is a good chance spacefaring beings would just want to stay in space. Still, they would like to (and have to) stay around a star at least some of the time to obtain energy and supplies, and repair and replicate their ships. All I am saying is that it is unlikely that everybody will pack up and leave again, together, after many generations of enjoying the sun and building ships.
I think you are much underestimating the effect of observation bias on current exoplanet findings. Allow me to cite from the original post:
@ljk: with all due respect, though I agree with by far most of what you are saying, one major correction is required: the vast majority of planetary systems discovered are *not* (super) gas giants in close orbit. Those were just the first systems to be detected, because the easiest to detect by means of radial velocity.
By now the vast majority of planets (in inner systems) are super-earths and sub/ice giants (Uranus, Neptune), the Jupiter class gas giants are much less common and the super Jupiters outright uncommon. And a smaller but still significant fraction (about 10%) are roughly earthlike.
So you are partly right and partly wrong here: the majority of (inner) systems are indeed different from us, but not the way you suggested (super gas giants) and a still significant part are more or less comparable.
To summarize: we are uncommon, but not that exceptional.
And I should have added: and certainly not unique as a planetary system type.
Ljk, Eniac, Rob Henry: fascinating discussion about the origins of life and the chance of alien civilization.
Eniac: although I remarkably often agree with you, I here digress on a few major points, let me mention three (of which the last is the hardest to explain), sorry if I repeat already made comments;
– You seem to equate the chance of abiogenesis and (any) resulting biological life to (the chance of) an alien civilization, as if the latter is an inevitable outcome of the first. It clearly isn’t and even if it were, it it takes such a long time that obviously alien intelligence and civilization must be a statistical rarity even among living planets. In other words: life may be very common and the universe may be teeming with it, but (advanced) intelligence at the same time very uncommon, let alone technological civilization.
– You state that there is as yet no evidence at all for a living planet. Well, that is obvious and logical, simply because we do hardly or not have any means yet to detect it (biosignatures). Even if the nearest sunlike stars had a living planet we would not know of it. The issue here is clearly not (yet) rarity but detection. I would even argue that with every next step we discover more and more factors that are favorable and conducive to life (sunlike stars, planets, earthlike planets, water, organic elements, etc. etc.) and real no show-stoppers.
– Quote: “In my view, it is likely that the universe is just big enough and has enough planets to bridge the remaining gap of “a few hundreds of orders of magnitude to one against””.
This one I find a bit hard to tackle, but my idea is that this is very unlikely, both from a statistical, scientific and philosophical point of view. On the basis of the Copernican and cosmological principles (matter and natural laws are universal) and real observation (the commonness of comparable objects and situations) I now dare to state that (nearly) everything in nature is gradual, i.e. following gradients and (near-)’normal’ distributions.
E.g., the sun is not a celestial object completely and fundamentally different from other stars, but a star of a type and class, ‘one in a row’, with which other stars share a greater or lesser similarity. The same seems to be true for the earth. And for elements and compounds (carbon, oxygen, organic molecules, water) and situations (light, temperature, etc.).
In view of this it is reasonable also to expect a whole gradual *range* of living conditions and living planets, varying from primordial pre-life, via primitive single-celled, mulit-celled, specialized organs, higher life, intelligence, …
From this viewpoint it is therefore also highly unlikely that there would be only one planet with ‘everything’, highly developed and highly diverse life, and for the rest just nothing at all.
Nature follows natural processes and laws. If matter and conditions are comparable, comparable processes and reactions will take place. Biochemistry may be special in certain ways, but is not different in this way.
That’s why I sometimes say that life is probably not so much a matter of chance but rather of the right biochemistry. And incremental growth of molecular size and complexity. And natural selection of that complexity.
Finally, I think it is flawed to talk about ‘a chance of 1 in xxx zillion’ orso, the way many people do, even from a purely statistical point: if you really want to talk chance, one should consider the number of *molecular reactions per time unit*, and that number is truly humongous.
This combination of right conditions, intrinsic biochemical characteristics of particular molecules, number of reactions per second, and incremental (selection of) complexity is what makes very large and complex molecules originate even in a lifeless environment, that should not exist from a ‘conventional’ statistical point of view.
Regarding exoworlds, I should have included the newer findings of relatively smaller worlds, though while we may have found some alien planets nearer in size to Earth, that does not mean they are actually *like* our world.
I have my doubts we will ever find a natural (aka nonterraformed) planet that matches ours to the point that a human could walk upon it without needing some kind of protective suit and breathing apparatus.
Also keep in mind I am from the time when the BIS star probe Daedalus was planned for a mission to Barnard’s Star because it was believed to have two Jupiter-type worlds circling it. In my day the only alien planets we knew about for certain were on Star Trek – and most of them were ridiculously Earthlike! :^)
It is nice to live in an era when one actively has to keep up with all the latest discoveries and information about real alien worlds.
@Ronald: You make many good points, including some that justly shame me for not arguing both sides enough.
– Clearly it is possible that life does not always lead to intelligence. This is merely my preferred assumption, and it is not needed as long as we discuss the probability of ETI rather than that of life. The Fermi argument is much weaker with regards to life than to ETI for the reason you point out. The reason I think that life -> intelligence is much more likely than chemistry -> life is that we have a fairly good understanding of the former, thanks to Darwin and paleontology, whereas we are clearly baffled by the latter, and will likely forever remain so.
– You are also right that the absence of evidence for life on other stars is primarily due to insufficient sensitivity. This is fairly obvious, but I could have stated it more clearly, I suppose. That is why I have focused on the fact that spacefaring ETI should have settled our solar system long before we descended from the trees or even left the oceans. That would be much easier for us to detect, unless the alien’s descendants were REALLY good at hiding.
– I do not share your conviction that it is “highly unlikely that there would be only one planet with ‘everything’, highly developed and highly diverse life, and for the rest just nothing at all.” I find it quite plausible, because we know for sure that this ‘everything’ you speak of all springs from the same origin, the LUCA and the (unknowable) history of its genesis.
I recall an earlier dissuasion here in which it became apparent, that if the appearance of intelligent life on Earth was as highly improbable as Ronald and others supposed then we would have to overcome one of these three problems.
1) that planets that generated environments in which increased data processing power was a sufficient advantage for life to begin the whole process were rare.
2) that the trend of increasing encephalisation quotients and neural complexity seen independently in many different groups here was a peculiar fluke.
3) that increased encephalisation only leads to true intelligence under unusual conditions.
The last of these was the hardest of me to fathom, since in Eniac’s words true intelligence seems “a real game breaker”.