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.
Almeno, su questo, aveva ragione Giordano Bruno…
Via Google Translate: “At least, in this, Bruno was right …”
Hi Paul
The ESO has the paper online…
One or more bound planets per Milky Way star from microlensing observations
…interesting that we can derive such planet abundance functions from the data. The current error bars mean terrestrials in the orbital distance in question are present around from 25% to 97% of stars. Jovian planets, interestingly, are much rarer, which is line with the core-accretion model of planet formation.
I would say this gives us a little more info for the Drake Equation, next is to narrow down about how many of these billions are in the Goldilocks zone.
If one in ten stars with an earth sized planet would have this positioned in the habitable zone , then there might be 20 such planets inside a radius of 50 LY.
Very interesting, more fuel for the Fermi Paradox. The microlensing finding that Jovians are relatively uncommon compared to the Neptune & SuperEarth classes is in agreement with Kepler. While some aver that Jovians are beneficial for life or advanced live, I am far from convinced of that.
Adam, thanks for posting the link to the paper. Now I have questions to put out there since I don’t have the references, especially [7] from 1992.
What is the minimum angular separation need to identify a lensing event from a planet (Jovian or super Earth)? As a Bayesian I have to wonder if they considered and evaluated alternative explanations for the lensing or false positives, such as “rogue” planets not associated with a star or pixel errors? In other words, just because a candidate occurred at low angular separation from a star is no guarantee that it was a lensing event.
Paul, a quibble on the caption on the image attached to this article. The exposure time can’t be 15 minutes since the stars or the observatory would be blurred. Is it seconds?
The frequency of habitable planets is only a trivial source of the very great uncertainties in the Drake Equation. Even full certainty about the number of habitable planets in our galaxy would not significantly reduce our uncertainties about the answer to the Drake Equation.
I just dug up an old post here from 2009: A Planetary Detection in Andromeda? that outlines a variant of gravitational microlensing (called “pixel lensing”) to detect exoplanets in the nearby Andromeda galaxy. If those methods prove fruitful (at the time there were only candidate, not confirmed, detections), then we’ll be able to get an independent sample of planet distribution within a spiral galaxy. It also seems that the 2009 pixel lensing group reached much the same conclusion about the prevalence of planetary systems as they did in this study: “It is in fact expected, and supported by observations and numerical simulations, that almost any star has at least a planet orbiting around it…”. This is nothing but good news, in my opinion.
So what are we to make of planets just smaller than earth in the habitable zone? the moon for example is not habitable in the ” avatar planet” sense. we need a great deal of technology to survive there, ( not just a simple pressure dome).
At what size can planet in and identical zone to earth around a similar star be able to support and atmosphere? Would Mars have a water rich atmosphere this close in ?
-And seriously what is the upper limit in size before the thick atmosphere causes a run away greenhouse effect? we live on a goldilocks planet in a goldilocks zone.
Ron S writes:
Ron, you’re surely right, it must be seconds. I’ll fix the caption — thanks for noticing this.
“The frequency of habitable planets is only a trivial source of the very great uncertainties in the Drake Equation. Even full certainty about the number of habitable planets in our galaxy would not significantly reduce our uncertainties about the answer to the Drake Equation”
True enough , but knowing THAT number will make it much easier and more likely to happen , that we get to know the NEXT number, which is the number of planets showing the chemical signature of life . If no signs of life can be found after the development of tools capable of spectroscopic analysis , then we have a” local” answer to the Drake equation , among others.
@jkittle – This online calculator lets you calculate the gas retention for any planet:
http://astro.unl.edu/naap/atmosphere/animations/gasRetentionPlot.html
Mars is just to small to retain a sizable atmosphere, even where it is now. Increase its temperature by bringing it closer to the Sun would just make matters worse. Mars lacks a strong magnetic field, so the solar wind can heat its upper atmosphere directly, leading to an even faster loss of gas.
If Mars were as dense as the Earth (5.5g/cm^3 vs 4 g/cm^3), it might be able to retain a sizable atmosphere at 1AU.
Clearly Venus has a runaway greenhouse, so it isn’t in the habitable zone.
By the way, do we have any better estimates on how long it’ll be before we know for sure whether Alpha Centauri has planets? You said last March that it might be a year or two out — so is there a chance we could be hearing something within the next few months?
Re Alpha Centauri, the three ongoing hunts are still in progress and we can only wait to see the result, but I would not be at all surprised to see something announced this year.
Ole Burde, Your correct, each step is one step closer to the answer of life , if not in the universe, at least in our galaxy. With all likelihood if we do not find a Oxygen/Nitrogen atmosphere planet with water in the Goldilocks zone within a 100 Light years, barring any type of FTL travel, interstellar travel will never become a major focus for humanity. Outside of interstellar probes and possibility of one-way trips, there would be no where for people to really go within a reasonable timescale.
Given the news that came out today about 1.6 planets per star being detected using microlensing detection methods, does anyone have an updated Drake equation “wild guess of the day”?
So far we’ve had the first planetary detection, the first relatively nearby exoplanet, the first super-Earth, the first exoplanet with maybe warm water temperatures, and now the first sub-Earth planets. Yet none of this has led to a sustained societal ground swell for an interstellar mission.
But we haven’t yet found the ultimate (Earth-sized in Goldilocks zone around a nearby star). Likewise, we haven’t yet discovered any even equivocal signatures for life on any of the exoplanets we’ve found.
My guess is that we will eventually find the ultimate Earth-sized in Goldilocks zone around a star within 50 ly of Earth but that it will be a bit too far for even a .1c craft to make worthwhile. I also am pessimistic that we’ll find an unambiguous biosignature but that we’ll probably find equivocal biosignatures that could be explained as natural (like methane on Mars).
I personally think that a science mission to a planet without even an equivocal biosignature with the main motivation to see if there is a hidden microbe is going to be a hard sell for two reasons. It will be too easy to ask, “What if the results are negative. Will the mission have been worth the billions spent on it”? Secondly, colonization of our own solar system will be in full bloom and so it will be a varient of, “Why do we need to spend money in space when we have so many problems on Earth”?
Rather, I think that what will make a nearby exoplanet valuable will be its “inhabitability” meaning what we can make of it. By 2030-40, I think that it will be clear that we can establish a human habitat on something as barren as the Moon and so any nearby exoplanet with reasonable gravity in the habitable zone (or somewhat beyond) will be an adequate target if the interstellar mission had a “manned” component to it.
I agree that the uncertainties in the Drake equation remain considerable, even having 10% or so of stars with planets in the habitable zone doesn’t lock down how many are actually potentially habitable and the uncertainties around the subsequent, biological, terms is very great. On that note I was wondering what people made of the idea of Dr David Grinspoon (Lonely Planets, 2004, if memory serves). Basically his idea is that rather than use a simple average for L, the lifetime of a civilisation, this is better treated as a probability value. For example, we could plug in a p value of 0.001 chance that a civilisation would go extinct in any one year (after technological take off), or any other value for that matter. Shermer argues for shorter average survival times or around 300-400 years, for example and other for longer.
The implication of using a p value is that a finite percentage survive for x years after technological take off. Grinspoon argues that if a civilisation attains the ability for interstellar travel it becomes essentially immortal. That might be a bit over optimistic, but probability of surivval would certainly jump considerably with each new star system inhabited by a culture. Exactly how long it would take to achieve interstellar flight is something of a guess, several more centuries seems to be a common estimate, so perhaps anything from 500 years to 1000 years after technological take off would seem reasonable at the moment.
If you do the maths of the above argument a p value of 0.001 gives around 18% surviving at least 1000yrs after technological take off, but one could plug any number into this, more or less. With the numbers of available planets and the timescale available, assuming models are broadly on track in suggesting most terrestrial planets would be considerably older than earth (Lineweaver 2001 suggested an average age of 1.8 billion years older than earth, but not sure if that is still current) then the emergence of civilisations would have to be an incredibly rare event not to have accumulated a significant number that had passed through the transistion Grinspoom argues for over a period of the past 2 or 3 billion years (the imagination boggles at what such a civilisation could be like, but…)
I wonder if the idea of near immortality for such civilisations is too optimistic and if so why…be fascinated to hear what people think. Whilst I can think of some things that could kill off such a civilisation the basic point seems logical to me and inclines me towards the zoo hypothesis or some variant on it…The alternative would seem to imply we are actually an exceptionally rare event which my Copernican instincts struggles with.
Greg
Even if no lifebearing planet is found at all , it could be the case that several planets vere found relativly close , that seemed fitting for being seeded with life (terraforming) , which could make them targets for human spacetravel at a later stage. This might seem far-out , but perhabs ways could be found to minimize the cost of sending such a “seed pakage” to a hundreds of close stars . Microbes are very tough creatures , incapsulated INDIVIDUALLY in a composite iceshell ,few of them might be capable of surving an entry to an atmosphere at relativistic speeds … which would eleminate the need for braking and so 95 % of the cost . If a fully developed microbial population was established on a chemically fitting planet , things might change VERY quickly , much like a combustion process.
Make that 36% surviving 1000 years at that p value – apologies, read off a figure from the wrong row! (not meant to be an argument for any specific value – just the general concept)
Absolutely fascinating news and publication!
The general conclusions are in line with Kepler (and HARPS), namely that gas giants are rather common, but (Neptune class) ice subgiants and super-earths the most common by far.
I wondered why the results for planets in the HZ are higher (10%) than the estimate of earth-sized planets in the HZ for Kepler and HARPS (about 1-2%, extrapolated), but I think this is, because this survey has 5 Me as a lower limit which is also the lower limit for super-earth, in other words: the 10% planets in the HZ includes *all* planets, not just earth-sized. Most of these will be ice giant (Uranus/Neptune) class or super-earth. The fraction of stars with a roughly earth-sized planet in the HZ will be significantly lower, but still encouraging, probably around the earlier Kepler and HARPS estimates of 1-2%, maybe a bit higher.
One more note of caution: the estimates are easily extrapolated to the entire MW galaxy, however, I doubt whether this is correct, because the halo and (since recent research results) much if not most of the thick disk are metal-poor.
I think, therefore, that it would be more appropriate to extrapolate to the galactic thin and intermediate disk, and within that to the (broad sense) solar type stars.
The number “L” is a great example of the vast uncertainties in other parts of the Drake Equation. The human species and its predecessors have already existed for 4 billion years. The proponents of L being less than billions of years haven’t presented any good arguments as to what existential threats (as opposed to mere disasters and temporary setbacks to civilization) are so universal that they would prevent our descendants (and the descendants of almost all ETI elsewhere) from existing for at least 4 billion more (in whatever form, as long as it is eventually capable of altering most of the surfaces of its galaxy). The average L will only be limited by the duration the universe can exist in a form that will support some form of intelligent being.
Ole Burde,
I like the idea except the issue of finding out if the microbes were successful. It would take hundreds or thousands of years just to get to a point where you can possibly detect you were successful. If it wasn’t successful do you send another spacecraft with microbes and wait another few hundreds of years? I don’t think humans are that patient to be honest. Now this may be doable if some form of nanotechnology was created, where we would know the possible success rates before we even launched them to a planet.
@ Anthony Mugan, What exactly do you mean by “technological take off” ?
Anthony:
Your Copernican instincts should be telling you only that the probability for life to form spontaneously is the same everywhere, depending on conditions. Not that it is of a particular size. From what little we know, it looks like that probability is very low. If I had to guess, I would say roughly the inverse of the number of all potentially life-supporting planets in the universe. This guess is perfectly consistent with the Copernican principle, with the Fermi “paradox”, and also with the anthropic principle.
Personally, I think life is fairly safe from extinction even now here on Earth: It has not happened in 4 billion years, why now (as Nick says). Even humanity, as an extraordinarily adaptable example of life, is likely to survive anything that nature can throw at us. Also, at least for now, anything we could inflict on ourselves. Survival could be with or without our advanced technology, which in any case will be quickly rebuilt.
After we settle the stars (and, inevitably, the whole galaxy), there is nothing at all that I can imagine to end the life of every single human descendant. If you can, as you say, let us know a specific scenario, please.
One of my main problems with the Drake Equation is that it assumes each planet can only produce one technologically civilized species ever. Intelligence doesn’t arise from a vacuum; it’s the end result of a long evolutionary process that generates the potential in multiple species. By now we’ve discovered that multiple other species are closer to human intelligence than we used to think, notably great apes, cetaceans, and elephants — and birds and cephalopods also show signs of surprising intelligence. So it seems to me that any planet that produces intelligence once is bound to do so again and again. True, if one species creates a technological civilization, it may well wipe out most of the other potentially or actually sapient species on its planet, particularly if it also wipes itself out. But it’s possible that at least one such species could survive (say, if it were in a different enough niche) and evolve its own civilization some millions of years later.
So there should probably be a multiplicative factor in the Equation relating to the number of different times a planet might evolve technological sophonts in its lifetime — though that might be hard to estimate and it would probably increase over time as neural evolution advances. (Yes, I know, evolution isn’t an “upward” process, but it does include innovations, traits that were initially absent but proliferate widely once they’re eventually introduced, like feathers or lactation or viviparous birth. The same would go for the components of intelligent thought and behavior.)
Nick, once more I think you make a powerful point, but I can’t resist a challenge. For the moment I can only think of two solutions to your dilemma.
1) There are self reproducing robotic berserkers in our galaxy, that are designed to seek out and destroy any technology that cannot identify itself as native to the originators of said berserkers.
2) The fundamental rules of our universe result in the destruction of any technology that is sufficiently advanced and inquisitive to contemplate and manufacture starships or make contact. The easiest way I can see this is if the discovery of experimental science is required to be a communicative ETI, and a disaster awaits when certain unnatural conditions are produced, the results from which would otherwise be very useful to that technology. One possibility that comes to mind is that a sufficiently powerful collider can produce a dangerous black hole or a particle than converts the (Earth) to strange matter. For this to solve Nicks dilemma, it is imperative that this result can never be proved as highly likely in any other way than the test itself.
There is a third alternative that should be mentioned because it is the standard copout. If we sieve for many different factors, none of which is that large, we can still get a low value for L. However we can turn that sieve on its head, and say that while any one factor cannot be ruled out as producing low L, a series of powerful and completely independent factors being responsible becomes exponentially more unlikely as an explanation as we increase the number of such factors required.
Rob, great comments.
1) Berserkers: if this is the case, why haven’t we already been wiped out? If the goal is to wipe out aliens, berserkers will have been programmed to wipe them out as early as possible. They should have killed us as soon as they saw any artificial structures like the Great Wall of China or the ancient canals in Egypt and Sumeria (or agricultural generally which greatly changes how the land looks from space). An even more effective berserker strategy might be to wipe out any life that achieves photosynthesis (again easily detected, and photosynthetic organisms are at the surface and thus relatively easy to kill). At the very least they should set up close surveillance as soon as they detect photosynthesis.
Also, they should have wiped out all the other ETI, making SETI pointless. Furthermore, the more surfaces the berserkers engineer the more effective they would be (collect more energy, radiate more energy, etc.). So we should detect galaxies where berserkers have engineered a substantial fraction of the surfaces. We should also detect galaxies that have been engineered for more benign reasons. Such engineering isn’t more difficult than spreading berserkers across a galaxy, and it’s hardly plausible that berserkers should be made by _every_ first civilization out of a hundred billion.
2) “The fundamental rules of our universe result in the destruction of any technology that is sufficiently advanced and inquisitive to contemplate and manufacture starships or make contact….For this to solve Nicks dilemma, it is imperative that this result can never be proved as highly likely in any other way than the test itself.” — This involves both speculative physics and an unfalsifiable condition, putting it beyond the realm of scientific inquiry.
To reply to questions:
Technological takeoff refers to the point when exponential technological development began, roughly late 18th century for humanity.
In terms of killing off a civilisation capable of interstellar travel I can imagine rare cosmological events such as extreme gamma ray bursts if only a few systems are colonised. Don’t think I could rule out disease totally, but clearly survival becomes much more probable.
Thanks for comments all
Gregg
There are several ways in which humans could reach another starsystem.
Very fast travelling is ofcourse the the best one , but if that dont work out there are other ways , which demand that we change ourselves AND our culture (or at least part of it) into something that will fit the jobdescription .
Historical evidence shows that past societies like bronce age Egypt vere capable of dedicating themselves for a thousand years to the gigantic projects of pyramid building . A small number of prehistoric peasants did this using only muscle power , brainpower and the power of their culture.
These prehistoric peoples have left for us a present , Santa-style, the gift of knowing that our species ARE capable of incredible feats of longterm projects, when a human society builds a culture that can incorporate the longterm goal into its core values.
“In terms of killing off a civilisation capable of interstellar travel I can imagine rare cosmological events such as extreme gamma ray bursts if only a few systems are colonised.”
At least a couple of problems with this:
(1) An existential threat of small probability doesn’t matter. It must have extremely high probability (c. 99.999999999%) to explain the absence of substantial surface engineering in other galaxies.
(2) It only takes a few tens of meters of ice or rock to protect against even a nearby gamma ray burst. So it’s not an existential threat to any species (like ours) that digs deep mines in planets or other bodies. Yet another example of a horrible, terrible disaster that is not an existential threat.
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
I predicted this type of response based on what was said in “The Eerie Silence.” If the emergence of life from non-life is extremely rare freak event, then the number of planets that exist would be of little significance. Personally, I am more of an optimist when it comes to life’s prospects for emergence elsewhere in the cosmos. I cannot help but think that plentiful organic matter, energy sources, and a quiescent environment in the habitable zone of a star would be enough to get at least simple microbial life started.
Ref. Scott G: when are the results for the Andromeda microlensing survey expected?
And would the transit method also work for the Andromeda galaxy?
Why look to low probability cosmological events for a doomsday scenario?
We are perfectly capable of dooing it with good oldfashionend nuclear war .
The probability of a runaway nuclear arms race among third world countries have now , with the iminent iranian event , passed the 50% mark . Before or later all local conflikts will have a nuclear component , and before or later the probability of this causing a large scale nuclear war will also pass the 50 % mark . The nature of a nuclear arms race is such , that it never ends before COMPLETE destruction is guarantied , and so we are not talking about a few minor Hiroshima-size bombs but rather a scenario where every little stupid dictator feels that he needs hundreds of BIG bombs , preferably hydrogen bombs . The only question that remains completely open is the specifik results of such a war , to what extend it will be a real setback for humanity as a whole…or what remains of humanity…
Ole Burke, as I have tried to explain many times that human style war is so unusual, that it seems hard to believe that we would find it even one other species in a million ETI. Perhaps the confusion is because hundreds of other Earth species engage in war. However these are (virtually) all hymenoptera species, particularly ants, lead by a female dominated genetic system. Their type of war is favourable under a wider degree of evolutionary circumstances than ours, and its nature is what we would call genocidal. Only one civilised race could develop to a technological state on its home planet by this type of war, and this “master race” would have amazing cohesion that would disallow internal strife (if this was not the typical result, then evolution would have disfavoured that type of war).
Despite much that you might read, war is a very unnatural result of male aggression or alpha male type domination. This is reflected in their being only one other (disputed) case of this type of war on our planet. Here males cooperate to deprive others of vital resources and female access. The cooperation and sense of fairness has to be so high, that the very high risk of fatality inherent in fighting other equals to the death is more than compensated by the increased allowance of their commanding alpha male of access by his subordinates to females. Obviously, such a commander is almost always better of fighting males from his own clan to increase his own female access (note also, that in this second case, a fight to the death is seldom necessary).
It might turn out that most other ETI’s are genicidal to others, but very few will be warelike, so that would make it extremely hard for them to selfdestruct in the way that you describe.
Ole, we’ve gone over 60 years without a nuclear weapon used in anger. Over a dozen countries have deployed them, yet only one has attacked their enemy with them. Furthermore, ongoing nuclear wars such as you postulate, while if they occurred would be terrible and horrible disasters, would not be an existential threats to our entire species. These facts strongly suggest that an ETI civilization has a substantial probability of surviving through its nuclear age.
Even if only a handful out the hundred billion ETI that must exist in other observable galaxies (if there are even odds of even one other ETI in our own), have passed through the nuclear phase and gone on to engineer the surfaces of their galaxies, we should be able to observe them. The lack of such observations must be explained almost entirely by some other explanation: an explanation that is universal and of exceedingly high (c. 99.999999999%) probability (or the lack of a necessary event of correspondingly low probability).
Remarkable that, when the news comes in about the abundance of planets, so many people start discussing the chance of another civilization, Drake and Fermi.
Understandable, but perhaps a bit premature, because even a tenfold increase in abundance of terrestrial planets does not change the fundamental rules of the game much, nor Fermi’s paradox.
I would rather argue, following Ole Burde (January 13, 2012 at 11:04) that an abundance of terrestrial planets is *always* good news, both from a scientific and from a human point of view. The former, because any (terrestrial) planetary discovery is fascinating in its own right and a potential platform for (any biological) life, the latter because terrestrial planets in the HZ of a (solar type) star will offer future targets for human settlement and terraforming, even and particularly if there is no indigenous (advanced) life.
Paul Davies statement “How much real estate is out there doesn’t matter” is, in this light, laughably off the mark. How much suitable real estate is out there (and how close) matters a whole lot.
Nick
Nuclear wars are not inevitable , but the probability wil increase dramaticly when the capability reach more and more countries . Human error is a statistical thing , if enough peoble drive their cars around on the highway it HAVE to happen before or later that somebody will make any concievable and deadly error .
A few drivers have managed not to run a read light for 60 years as you say, but now were going to have hundreds , and some of them are drunk .
If, in 60 years of having multiple armed nuclear combatants, we came close to obliteration (Cuba Crisis) once, and that was 50/50 either way, then the odds of no nuclear conflict between equals seems to have a characteristic time of 60 years. Given a couple of hundred years, the odds of survival are very low.
Ronald: “terrestrial planets in the HZ of a (solar type) star will offer future targets for human settlement and terraforming.”
There’s a paradox here though. If or when we achieve the capabilities needed for a many centuries long manned interstellar voyage — large scale manufacture of cheap propellant from off-earth sources, fusion power, enclosed ecologies, and probably the most difficult problem of all, a self-sufficient yet high-tech economy that can fit inside a starship — by that time, we won’t need to live in the HZ any more. We will be able to live almost anywhere is space that has the basic resources (e.g. water and metal for building space industries and habitats).
At that point, gravity wells will be less attractive as places to live and thrive. Asteroid belts, moons, and dwarf planets with a nice mix of ice and metal will probably be more attractive, as there one can develop a much larger interspace economy that doesn’t require the high transportation costs of a gravity well, and can create larger livable spaces than by sticking to the two-dimensional surface of a planet. Our discovery of large ring systems and asteroid belts may well be more important to future human interstellar voyagers than our obsession with finding planets just like our own.
Adam: “we came close to obliteration (Cuba Crisis) once”
The Cuban Missile Crisis, and the Cold War generally, did not pose an existential threat to our species. If the U.S. and the Soviets had both fired off every missile in their arsenal, this would have been an unprecedented horror no doubt, but hundreds of millions of people (at least) would have survived.
Much less would some smaller countries nuking each others’ cities, per Ole, constitute any sort of existential threat to the long-term survival and expansion of human civilization. Quite the contrary, via modern media we’d learn in gruesome detail the horrors of nuclear war and learn how to avoid it altogether or at least survive it better in the future. Humans can adapt to many kinds of very unfortunate environments.
A fascinating discussion as always. If I am getting the correct impression then a fair summary so far might be:
a) habitats are plentiful (probably into the billions in terms of potentially habitable planets in our galaxy alone, with a number of other options for arbitrarily advanced civilisations as well, as per Nick’s comments)
b) The probability of humanity surviving the next few centuries and attaining the capability for interstellar travel is not zero, although consideable debate around the risks of major setbacks which might reach the level of knocking civilisation back by some centuries. or possibly even worse. The majority view seems to be that the probability of surviving that long is substantially greater than zero, but with considerable variation in views.
c) Once colonisation in / around other star systems has been achieved the general view seems to be that Grinspoon’s idea has merit, and such civilisations (if any) would probably survive more or less indefinately.
d) Points a – c seem to focus the key uncertainties onto the origin of life and the probability of a technological civilisation actually arising, i.e. the probability that the ‘random walk’ like characteristics of evolution would lead to a species with enough intelligence and other capabilities to build a technological civilisation within the habitable lifetime of their home planet. As far as i can see the only value we can rule out for the product of these two factors is zero, on anthropic grounds. This leaves open the possibility that the p value could be as low as Eniac suggests.
Doubt we shall get too much further with the civilisation aspect of this one in our lifetimes unfortunately, although the p value for life itself might start getting a bit more constrained in coming decades if we get suitable measurements from exoplanets, and possibly in due course detection of microbial life elsewhere in the solar system. No idea what computing power would be needed to model evolution, but that might eventually be a possible way into it.
Thanks for the debate…
Nick, yes, I am aware of the (seeming) paradox.
However, I believe that humans will keep living on and searching for earthlike planets, even if we wouldn’t have the strict need for them anymore, for the very biological facts that make us human: we like earthlike ‘garden’ planets, just as we like park-like environments to live in, we keep creating them in suburbs, etc.
It is in our genes, literally.
So, I actually think that humans will keep settling and creating (i.e. terraforming) earthlike planets, *particularly* once we have the technology and wealth to do essentially what we like, not out of bare necessity but for enjoyment. Similar to rich urbanites creating their dreamhouse with large garden in the suburbs or a so-called luxury ‘farm’ in the countryside.
Related to this would be the desire to study and ‘enjoy’ discovered living (earthlike) planets.
A second reason to keep settling and reshaping planets is survival (I am trying to avoid a repetition of previous long discussions here about space-colonies versus planets): even if and when we are able to live in large space-colonies and even if our descendants would love it, planets have proven themselves as relatively stable long-term platforms for life. Ok, s..t occasionally happens locally or regionally, but an earthlike planet can survive for gigayears.
There is even cost-efficiency in this: an earthlike planet easily has some 100 million km2 of livable space, compared with maybe 1000 km2 for a very large space-colony, i.e. 100 thousand times as much. What would be the cost (net present value) of such a space-colony? Easily 100 billion US$? And what would the lifespan of such a space-colony be? 1000 years for total depreciation?
Easy to estimate that an earthlike planet, if and when it could be reached, would always be vastly more cost-efficient per area and time unit.
Given continuing technological development ánd the discovery of relatively nearby terrestrial planets, even without FTL, I foresee a human future of 1) drastic life-extension, 2) some form of artificial hibernation, 3) sub-c interstellar spacetravel.
Of course, with some form of breakthrough FTL propulsion the whole picture would *dramatically* change in favour of planetary settlement.
I do also foresee a future with large space-stations, even more or less permanent space-colonies, besides planetary settlement, not instead of.
A future with exclusively space-colonies and without any significant planetary settlement would most probably be the result of a lack of (reachable) terrestrial planets, not a perceived redundancy of them.
The scenario where a runaway nuclear armsrace takes place among hundreds af nations , would (as Nick said) not necesarily be threat to humanitys long term survival . On the other hand , it might gobble up a critical amount resurces and raw materials at a critical point in history , resources which would then later become more expensive when they start running out .
The possibility of achieving starflight might only exist in a limited “window of probability” where a surplus of resources can be expended . A few years later worldpopulation might have grown to an extend where ANY kind of surplus wil needed to soften the impact of frequent massstarvation events and other disasters , among them perhabs nuclear wars .
Further out in the future it becomes impossible to predict anything , but this scenario is a possible one , and it deserves consideration here because it demands to rethink how much TIME will be avaiable to achieve starflight . Perhabs it will be necesary to speed things up .
Ronald, you make a great point about human instinct as with suburban lawns and gardens. However, just as suburbs aren’t really natural, it’s highly probable that these instincts will be satisfied by putting sufficiently large gardens and habitat reserves inside space colonies.
I suspect your number for the typical size of a space colony is far too small. If we can make a starship that can fit in a high-tech economy, it will require far more than 1000 km^2 of space. One needs tens of millions of people at least to sustain anything close to the division of labor required for our high-tech economy. Improvements in technology may eventually reduce this by one or two orders of magnitude, but that’s still a lot of people.
Also, there’s no reason that the basic structure of a space colony shouldn’t last several orders of magnitude longer than a building on a planetary surface (thus in terms of reliability, maintenance costs, and lifetimes, better than buildings on a planetary surface, where they tend to be subject to a variety of hazards from atmosphere, water, etc.).
Furthermore, given the abundance of resources and the very low transport costs in asteroid belts, a space colony there will eventually cost no more than pennies per km^2, similar to planetary surface real estate costs but far more accessible due to lack of a deep gravity well. Indeed, the lack of (or lower artificial) gravity and the far lower cost of transporting materials will probably make construction costs far cheaper than on the surface. Furthermore, such low costs will also be required to build the manned starship. If we can’t build very large and very low cost space colonies then we won’t be building any manned starships either.
Ronald, let’s assume that one day we can live anywhere as you suppose. Economies tend to grow exponentially, and so do most human populations.
To start with, I think that you are on track in psychology being a very powerful influence on the patterns of future human expansion. It may well turn out that humans prefer that “natural feel” of a planet rather that an environment that is built to specifications that perfectly match our visual perceptions of utopia. However psychology is currently an abysmal science so it is hard to draw predictions from it except when choice preferances seem obvious.
If almost all of us prefer Earth, trillions of us could still be fed from farms in space and our great wealth could pay for this privilege, but just from the heat dumped there, this would force the Earth to become a barren landscape of our buildings, whereas the tiny number that chose the colonies would by surrounded by flowing water, plants and selected animal life. I’m trying very hard but I can’t imagine myself staying here, and I suspect that even you would pay to join the colonies given that alternative.
Anthony Mugan, The “random walk” school of evolutionary biological only tries to explain why some creatures are more complex than others when evolution should, if anything, select against it. Data from our biosphere shows that two traits for additional complexity are so powerfully selected for that they can’t be modelled on this random walk basis, namely brains and immune systems. There are clear indications that these have tended to gain complexity with time in many different groups.
Rob: Good point about the brains and immune systems. These happen to be the tools of biological and good-old fashioned mechanical warfare. You might want to add chemical warfare, which has given rise to great complexity in biology, and to which we owe advances such as antibacterial drugs and nuisances such as dangerous spiders and snakes.
It is not a random walk that produces such complexities, it is the ever escalating competition to outsmart others or be killed. I suppose this does not fit in with your peculiar theory that human style warfare is unusual or unexpected somehow, but so be it.
Adam:
The flaw in this argument, I believe, is the “between equals” part. Since the end of the cold war, the US has pulled ahead of everyone else to such a degree that there can be no challenge from any “equals”. It is at this time unclear is this is a temporary or permanent state of affairs, but it is quite different from the past. It is possible, even likely, that the Earth has become to small and the US too powerful for there to be room for multiple “equals” anymore. And this could well be a good thing for our future.
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.