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Space Science

Habitable Planets May Be Common 346

Posted by Hemos from the maybe-counter-earth-exists dept.
swight1701 writes "New Scientist tells us, "one in four of the planetary systems identified to date outside the Solar System are capable of harbouring other Earths, say astrophysicists, a much higher proportion than anyone expected." Two seperate groups have come up with results that line up with each other, the latest one using simulations of 85 systems. Warm up the warp engines, time to go planet hopping!"
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Habitable Planets May Be Common More

Habitable Planets May Be Common

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  • Alright, I can't wait till we start drilling for on every planet. That will be so cool.
    • So you are implying that we have destroyed this one? I'm curious... do you walk to work? do you own a car? Do you use electricity? Do you heat your home? Do you cool your home?
      Well I guess that makes you part of the problem then doesn't it?
    • Please. A million years from now, nobody will remember or care what happened to one little planet orbiting one uninteresting star in the backwater of yet another generic spiral galaxy.

      So what if we turn this place into a deadly wasteland of death? There are far worse environments by the billions. By the time the history of the human race actually gets properly started, nothing that happened here will matter at all.

      • Re:more ecosystems to destroy !!! (Score:4, Insightful)

        by webster ( 22696 ) on Sunday January 05, 2003 @02:07PM (#5020335)
        By the time the complete history of the human race human race can be written there won't be anyone interested enough in us to write it.

        The history of the human race already has been started, written by the only creatures in the multiverse likely to find us interesting, rather than fascinating (or appalling?)

  • But... (Score:5, Insightful)

    by unterderbrucke ( 628741 ) <unterderbrucke@yahoo.com> on Saturday January 04, 2003 @01:11PM (#5014409)
    "one in four of the planetary systems identified to date outside the Solar System are capable of harbouring other Earths"

    The operable word here is capable.
    Half of these planets won't have oxygen, another 49.9% will be too cold.
    This study is referring to the distance of the star to the planet being far enough that the sun doesn't fry the planet.

    • Re:But... (Score:5, Informative)

      by chill ( 34294 ) on Saturday January 04, 2003 @01:28PM (#5014496) Journal
      "This study is referring to the distance of the star to the planet being far enough that the sun doesn't fry the planet."

      Actually, it referrs to a bit more than that...

      It referrs to the ability of an Earth-sized planet to exist in a stable "habitable zone" orbit (not too hot, not too cold).

      Not being torn apart or having a perturbed orbit due to the proximity of gas giants, etc. is another big factor.

      However, it isn't exactly time to start looking for a nice time-share condo on Ceta Alpha V, yet.

      • Re:But... (Score:2, Funny)

        by Toraz Chryx ( 467835 )
        Wait till AFTER Ceta Alpha VI explodes, then the property prices on V will drop drastically.
      • Not being torn apart or having a perturbed orbit due to the proximity of gas giants, etc. is another big factor.

        I don't see what the problem would be with an earth-size moon orbiting a gas giant within the habitable zone ...

        Ceti Alpha V

        ... unless it was theh radiation, Cap'n?

    • Re:But... (Score:5, Informative)

      by panurge ( 573432 ) on Saturday January 04, 2003 @01:42PM (#5014586)
      Sorry, but the Earth didn't have much oxygen until life started producing it. That's the history of life: it changes the planet to suit itself.

      We do it, but even bacteria do it too. As plants have reduced the amount of carbon dioxide in the atmosphere, different dominant plant families have arisen able to survive in the low-CO2 environment. Insects were big at one time because there was more oxygen in the atmosphere, now the species are smaller because there is less. The idea that life requires 0-35C, 20% oxygen, is based on a static view of the world which, as our genetics lecturer once remarked "Unfortunately for some religious groups does not accord with any of the evidence."

      • Re:But... (Score:4, Informative)

        by airuck ( 300354 ) on Saturday January 04, 2003 @02:13PM (#5014729)

        For an example of a very large prehistoric insect and some discussion of fluctuations in the Earth's oxygen levels see Meganeura monyi [flappia.com] and:

        Dudley, R. 1998, Atmospheric oxygen, giant Paleozoic insects and the evolution of aerial locomotor performance. Journal of Experimental Biology. 201: 1043-1050.

        Graham, J.B., Dudley, R., Aguilar, N.M., and Gans, C. 1995, Implications of the late Paleozoic oxygen pulse for physiology and evolution. Nature. 375: 117-120.

    • Re:But... (Score:3, Interesting)

      by Bicoid ( 631498 )
      Ummm....

      Not to be a smartass or anything, but we shouldn't BE looking for a planet with an atmosphere more or less like ours. Earth didn't start out with lots of water, OR with an oxygen atmosphere. We were a rock with lots of iron, manganese, and silicon oxides with a hydrogen cyanide atmosphere. It wasn't until after a bunch of comets struck the earth and deposited a bunch of water that we actually had oceans. And it wasn't until our atmosphere was converted by photosynthesizing bacteria that we got an oxygen atmosphere. Even if we DO find live, it's more likely we'll find chemosythetic microorganisms or something similar. It's very unlikely we'll find a planet all ready for us to drop colony ships and stick people on.

      Regardless of how common earth-like planets are, we're going to need to terraform them so they'll be habitable for us. We'll need to engineer bacteria similar to the ones which converted our atmosphere and we'll likely also have to redirect some large comets from their outer fringes to make a water ocean.

      Part of me just keeps wanting to yell at the astrophysicists, astronomers, and sci-fi authors who talk about the difficulty of finding a habitable planet. Please, these people need some paleontology and historical geology courses under their belt before they can go off spouting about "habitable" planets. Regardless, we're going to have to MAKE those planets habitable or else we're going to have to change ourselves so that we can inhabit those planets. It's common sense.

  • They say habitable... (Score:5, Interesting)

    by doobie ( 2546 ) on Saturday January 04, 2003 @01:13PM (#5014419)
    They say their are habitable for life...why do we always assume every life form will be exactly like us and need our environment to thirve? For some other form of life they may thrive on Venus or Jupiter.

    • Re:They say habitable... (Score:5, Insightful)

      by th1nk ( 575552 ) on Saturday January 04, 2003 @01:24PM (#5014473)

      They say their are habitable for life...why do we always assume every life form will be exactly like us and need our environment to thirve?

      Up to this point in the history of our world, certain things are required for all life as WE know it. If we're searching for life on other planets, wouldn't that be a good place to start?

      • Re:They say habitable... (Score:2, Insightful)

        by doobie ( 2546 )
        But we have found life thriving in places like volcanic ash spewing from the sea floor...we never expected to find it there... What you are searching for always ends up being in the unexpected places.
      • [...] all life as WE know it. [...]

        Analysis, Mister Spock!

        It's life, Jim, but not as we know it,
        not as we know it,
        not as we know it.
        It's life, Jim, but not as we know it,
        not as we know it, Captain.

        [...]

        Prepare pathetic aliens:
        Ha-ha! We come in peace, shoot to kill,
        shoot to kill,
        shoot to kill.
        We come in peace, shoot to kill,
        shoot to kill, men.

    • Re:They say habitable... (Score:5, Funny)

      by Waffle Iron ( 339739 ) on Saturday January 04, 2003 @01:33PM (#5014524)
      They say their are habitable for life...why do we always assume every life form will be exactly like us and need our environment to thirve?

      Nobody's saying they are exactly like us. In fact, on average they have larger breasts, greener skin, heavier mascera, and wear shorter miniskirts.

    • Right. But for now, the only evidence of life we have is here on earth.
      Nobody is saying "There can't be other kinds of life"... but to speculate on the odds of it is meaningless as we haven't found any yet.

  • Huh? (Score:5, Interesting)

    by Quixote ( 154172 ) on Saturday January 04, 2003 @01:13PM (#5014421) Homepage Journal
    Quoting the article:
    The researchers found that around a quarter of the systems contained regions where life-friendly planets could in principle exist.

    If the requirement is that there be a "region" around the star where a planet could have water in liquid state all-year-round, wouldn't almost every star satisfy this? Every heat source has a distance at which it feels "nice" (as anyone who's been at a campfire can attest to).
    Maybe I'm missing something here (which has been known to happen :-)

    • As I understood the article, the gravitational pull of the gas giants that can be seen from earth can "pull" smaller (sofar invisible earth-sized) bodies out of this region if they are in the "wrong" area.

      Depending how you look at it (glass half full/empty) it turns out that the giants are in the wrong spot three out of four times...

    • Re:Huh? (Score:3, Informative)

      by imnoteddy ( 568836 )

      If the requirement is that there be a "region" around the star where a planet could have water in liquid state all-year-round, wouldn't almost every star satisfy this?

      From the article:
      The first thing they looked for in each system was whether a small terrestrial planet could exist in a stable orbit. The gravitational tugs exerted by gas giants can force smaller planets into unstable orbits or eject them from a system altogether.

      So the requirement is that there be a stable orbit within the distance range where water would be liquid.

    • Every star might have a comfort region, but not every star has (a) any planets (b) earth-size planets in that region in a stable orbit. Life as we know it isn't going to develop on a gas giant, or outside that 'region'. The 1 in 4 number is of stars that have been determined to have planets, i.e., 1 in 4 of those stars has earth-size planets in that region.

  • In other news.... (Score:5, Funny)

    by karlm ( 158591 ) on Saturday January 04, 2003 @01:14PM (#5014424) Homepage
    The Raelians have announced their first colonizing ship full of expectant clone mothers is due to arrive in the nearest system in question sometime next month.

  • Rolling the dice (Score:3, Interesting)

    by Ninja Master Gara ( 602359 ) on Saturday January 04, 2003 @01:16PM (#5014432) Homepage
    Then we'll have to figure out just how rare liquid water is, oygen rich atmospheres etc etc

    1 in 4 might be good for balls of rock, but it doesn't quite match "Earth".

    • Re:Rolling the dice (Score:4, Informative)

      by cornjchob ( 514035 ) <thisiswherejunkgoes@gmail.com> on Saturday January 04, 2003 @01:52PM (#5014631)
      Oxygen and water? Again, people are assuming that earth's atmosphere and other conditions need to be recreated to sustain any life--bullshit, honey. remember, oxygen is a corrosive gas. And many organisms even here survive fine without it; even without water. Once and for all, this paradigm of everything having to be like us needs to be blown out of our systems like an explosive kidney stone. Think outside the box, or don't think at all.

      Didn't mean to tear ya up if it came across that way; I just get frustrated very easily.

      • This is true, but one can't deny that if we find out that oxygen and water is relatively common, that would still mean a lot, since our own planet proves that these elements are vital for at least one kind of ecosystem.

        And even if you get frustrated easily, that doesn't mean you have to show it in your post. :-)

  • intelligent life in the universe (Score:5, Interesting)

    by cschieke ( 308178 ) on Saturday January 04, 2003 @01:17PM (#5014439)
    I took a college course called "Intelligent life in the universe" (god I loved college). Where we learned basically:

    1. What we know it takes to support life
    2. What living objects are typically made of (carbon based compounds)
    3. What percentage of stars have planets around them, what percentage of those planets are the proper distance away from the star the orbit (which changes based on the size of the star)
    4. a bunch of biology, and some other related stuff

    It boiled down to the idea that the universe is soo huge that IF we're the only intelligent life in the universe, that there must some type of "god" and if we're not, well then the evolutionary theories are probably fundamentally correct (doesn't mean there isn't "god", but not in the literal old testament sense).

    see, no real hard conclusiions only questions, cause there is always another level deeper to go.

    • I've often wondered how the worlds religious leaders would react if a flying saucer landed on the lawn of the white house. The Catholic church only just admited that dinosaurs existed, how would they handle another inteligent species?

      • Comment removed (Score:4, Interesting)

        by account_deleted ( 4530225 ) on Saturday January 04, 2003 @01:35PM (#5014539)
        Comment removed based on user account deletion

        • The Catholic Church (Score:5, Interesting)

          by dachshund ( 300733 ) on Saturday January 04, 2003 @10:53PM (#5017178)
          Basically, I've never heard anything about the Catholic church disputing the idea of extinction or dinosaurs. Or are you just using that as a type of example?

          There was a great deal of contention prior to 1950, when the Church officially announced that it would tolerate its members believing in the Theory of Evolution. This ocurred when Pope Pius XII produced the papal encyclical entitled "Humani Generis". His statement said, essentially, that it was alright for Catholics to believe whatever scientific theory they wanted... then went on to stress that the Theory of Evolution was still unproven.

          The above poster may be referring to the much more recent (1996) statement by Pope John Paul II entitled "Truth cannot contradict Truth". In this document, the pope not only accepted the ToE as being in line with Catholic beliefs, but he stated that it was "more than a hypothesis". This was the first time that a Pope officially supported the ToE, rather than merely tolerating it.

          So it's more or less correct that the Church only officially got behind Evolution recently, though I don't know if it's accurate to say that they disputed the existence (and extinction) of the Dinosaurs.

          The same applies to fossils. If fossils found far far back didn't belong to deceased animals, then that means (to religious people) that God put them there (the bones). But then that contradicts the watchmaker theory. Why would God create essentially fraudulent records?

          It seems that the existence of fossils could be construed as incompatible with the Watchmaker theory anyway. Why would God, in the process of creating an intricately designed world, feel it necessary to create creatures (actually, entire ecosystems) that would ultimately be unable to survive?

          You could respond that God is ineffable, but that same logic pretty much works for the folks who think God created fake fossils and buried them in the ground. The point is, once you allow for the existence of God, rational arguments are pretty much always vulnerable to the divine wild-card.

    • Wait...you were told that if we're the only intelligent life form in the universe (which isn't exactly easy to verify), there _must_ be some sort of "god"? Seems like a non sequitur at best to me.

      Was this course offered by the department of theology by any chance :) ? Seriously though, you'd think a science professor would know a thing or two about Occam's razor...
      • I think his meaning was more rooted in the probabilities of such events. Take the following hypotheses:

        Hypothesis #1: We are the only life in the universe. Given the stupendous, enormous, unfathomable size of the universe, the billions of years of possible evolution, the quadrillions of possible planetary systems, and the innumerable number of possible chemical reactions, if we're all that there is then it goes against every probability that there is. This could be a powerful argument that something, somewhere, somehow put us here.

        Hypothesis #2: We are not the only life in the universe. If this is true (and I belive that it is) the life should be everywhere, but due to our current technological limitations we're too spread out to find each other just yet. The more life we find, the less likely it is that life is the result of some external influence.

        Corollary to Hypothesis #2: If life is everywhere in the universe, one could argue that the preponderance of life indicates that the universe was engineered in such a fashion to create life. This again implies the existence of a creator with a master plan for us, life in general, or the universe itself. Indeed, it is possible that our "laws" of physics, matter, energy, and so forth were engineered at the time the universe was created, and all God has to do now is sit back and watch us develop. This, then, raises the age-old question of whether we really have free will or if our destinies are already charted. Heisenberg says no if for no other reason than quantum mechanics, but can we ever really know?
    • "It boiled down to the idea that the universe is soo huge that IF we're the only intelligent life in the universe"

      Ah, but is intelligent life all that matters? For example, I wouldn't say we're the only intelligent life on this planet, but we're the only ones capable of abstract language (and possibly abstract thought because of it) and tool use.

    • Maybe you're referring to the Drake Equation [lifeinuniverse.org]? The problem with the drake equation is that you can plug reasonable values into it and get zero and you can also plug reasonable values into it and get a billion. It's really just speculation.

      I'm more curious about what was the university/professor that made a statement along the lines of "if we are the only life in the universe then there must be an intelligent creator"

    • Look at every historical example of first contact between two cultures, especially two cultures of unequal technological advancement. The historical legacy of unmitigated disaster would be an excellent reason for aliens to avoid us and for us to avoid aliens. It might even be a good reason for them to avoid each other.

      Would we really want to repeat what happened when the Spanish colonized / conquered the Americas and almost completely wiped out the native Mexica. I would hope that for most super-civilizations, one or two instances of unintentional genocide would be enough to encourage them to stay home.

      Look at us, if we made contact with another species we'd turn them into a thrid-world planet. Buy our products or DIE!!! Adopt our economic models or DIE!!!

      Maybe different species are not really meant to get along, or maybe there is no evolutionary advantage early on of developing "get along with other species" traits. Either way, I do honestly fear that whatever unlucky civilization we encounter first - we're going to wipe out, whether we mean to or not.
      • I think the whole interstellar imperialism depends on the technology of the species we encounter. If they are technologically superior, they may very well turn our species and our sphere of influence into a colony. If they're less advanced, they will likely end up as dependant on us, or perhaps may get wiped out. If we have equal technological levels we may see each other as competitors and try to eliminate the other's threat using either economic forces or via plain old war. Of course, there's the possibility that they have absolutely no interest in us, either due to vastly different biologies or simply their psychological profile. It's even quite possible that they will simply absorb us as America has done to many other cultures.

        But to assume that humanity will undoubtably subjugate any other interstellar species is anthropocentric and ignorant.
        • I didn't say undoubtably, and if you read my post again you'll see that I didn't.

          If you're going to form opinions you can either beak off on speculation, or you can go with what you know. Any discussion of human-alien first contact is going automatically be anthropocentric because we are human, all we know is humanity and as of yet the aliens are an unknown quantity. So what we know:
          * Humanity is an agressive, competitive species.
          * Pretty much all historical instances of first contact between human cultures have been instances of tragedy or war (take a serious look at history). When there is an inequality of technology, tragedy, when the cultures are relatively equal - war.
          * Encounters with new animal species almost always go badly for the non-humans, regardless of the intelligence of the species. Dogs and cats are pretty much the only animals in all of history to do well by associating with humans.

          * Finally, any potential alien civilization is a complete unknown. Maybe they'll be able to hold their own, maybe not... but if you're a betting man, bet on the species you already know is a viscious effective killer.

          Oh, and as a side note the odds of meeting a technologically equal civilization are close to zero. Either we come to them, or they come to us. The chances that we meet half way...
    • that IF we're the only intelligent life in the universe

      We are intelligent?

  • You won't know in your lifetime (Score:4, Insightful)

    by Damek ( 515688 ) <adam@nOspam.damek.org> on Saturday January 04, 2003 @01:17PM (#5014440) Homepage
    No matter how many statistical guesses different scientists make, the question of habitable planets, not to mention the question of other intelligences, will not be answered without actually going out and visiting them. This will not happen in your lifetime. You will not know. Sorry!
    • No matter how many statistical guesses different scientists make, the question of habitable planets, not to mention the question of other intelligences, will not be answered without actually going out and visiting them. This will not happen in your lifetime. You will not know. Sorry!

      Might want to see the movie "Contact" to update yourself on _how_ we will be able to detect life somewhere else. We do not have to go anywhere. All it takes is a good telescope (got those) and a lot of sifting through the data (SETI et el). Whether that will happend in our lifetime is part of scientific guesswork.

      I like the research that refines our understanding of the (habitable) universe and helps us create a scientific model that allows predictions for 'life out there'. I'd like to stress the _scientific_ nature of this research. The splitting of the atom, the landing on the moon, the cloning of molly and most other human achievements will pale in significance once we proof that earth is not the only place for life in the universe.

      "If we where the only life in the universe, wouldn't that be an awfull waste of space?"
      Now think Occams Razor!
    • No matter how many statistical guesses different scientists make, the question of habitable planets, not to mention the question of other intelligences, will not be answered without actually going out and visiting them. This will not happen in your lifetime. You will not know. Sorry! Well, for the habital planet part you are simply wrong. Within 10-20 years there will probably be telescopes powerful enough to see Earth-sized planets, perhaps even their continents. These telescopes are already on the drawing board.

      For the intelligence part, you are certainly right that we wont be able to visit anybody in our lifetime (except possibly in the unlikely event that intelligent life is found on Europa). But that is not the only way to find out for sure. They could come and visit us, or we could intercept a signal (like radio, or laser).

      Tor

  • Habitable is a long way from hostipible (Score:3, Interesting)

    by saskboy ( 600063 ) on Saturday January 04, 2003 @01:18PM (#5014445) Homepage Journal
    This isn't too surprising since all a planet has to have to be habitable is a small enough mass to not crush our bodies, ideally a natural radiation shield, and only enough heat per square meter to provide energy while not cooking our structures. Some natural resources that we can eat and drink would be nice too.

    Jupiter like planets will have satellites that might have the right sized radius to allow us to live on them. They don't all have to be planetesimals like Mars.

  • Scientists (Score:5, Interesting)

    by CatWrangler ( 622292 ) on Saturday January 04, 2003 @01:22PM (#5014459) Journal
    First they tell us the earth ain't flat, then the Universe doesn't resolve around our planet... then the fake moon landings, now this. Good thing we have fundamentalists around telling us it isn't so. Seriously, unless there is a nature of physical or sound travel that we are unaware of, it really doesn't matter much to us that much if there is a civilization 1000 light years away. In the 2,000 years it would take to get a super amplified light message to them and back, will we still be around to listen?

  • Okay who's with me? (Score:5, Funny)

    by nightherper ( 635698 ) on Saturday January 04, 2003 @01:23PM (#5014469) Homepage
    Let's build a freedom ark and run off to a new planet and leave the RIAA MIAA DCMA DRM MS BG and any others that we don't like/need/wish would go the hell away behind.... Oh and we can't forget to grab some fine female genetic specimens on the way out the door.
    • Technically speaking, wouldn't it be easier just to create a giant, artificial island in the middle of the Atlantic, and our own geek government, outside the jurisdiction of said entities? I'm not saying such a thing would be easy, but a heck of a lot easier than loading 5 million geeks into an ark ship and shooting them off to Tau Ceti.

      Most of our problems that people think should be sovled by space exploration/colonization have nice, terrestrial solutions. At least, until the sun goes red giant on us...
    • Some? Why not grab all the fine female genetic specimens?

  • The Drake equation (Score:2, Funny)

    by Anonymous Coward
    The Drake Equation is a simple little formula that allows one to calculate the number of civilisations in the galaxy. It is a tried and tested scientific means of working out the number of civilisations that pose a threat to the USA and indeed the world.

    Here, using the latest information available to science and the most up to date techniques, I have recalculated the values for the Drake Equation showing that the National Defense Establishment must have its funds greatly increased (an unconventional view perhaps, but I am not biased and trapped by the establishment as certain low browed arriviste scoundrels are).

    For our readers who don't know simple maths (surely the vast majority of you), you need not worry - this is so simple a child could master it.

    Here is the Equation:
    N = R* × fp × ne × fl × fi × fc × L

    Let us run through the values one by one.

    N = The number of communicative civilisations.

    This is the thing we are trying to work out, and it equals the multiple of all those funny symbols on the right hand side of the equals sign (again, for those of you who don't know any mathematics, I mean that when you multiply all the things on the right, you get the thing on the left. The symbols represent numbers, the numbers we are putting values on).

    R* = The rate of formation of suitable stars. In other words, the rate of formation of stars with a large enough habitable zone (the bit Earth is in, not too hot and not too cold for life) and a long enough lifetime for life to develop.

    This one is measured in star systems per year. Now, our galaxy is about 5 billion years old, and has about 5 billion stars. So the rate of formation is obviously 1 per year. The number of suitable stars is smaller though. It is obvious that all stars have a habitable zone - even the coolest of brown dwarves will have a region close enough to be inhabitable. So the only determinant we need worry about is lifespan. The only stars that don't live very long are giant stars, and they are very rare - only one star in a thousand is short lived. So we can safely say that R* = 0.999. This is established fact, there really isn't any other plausible value.

    fp= The percentage of those stars which have planets. Well, here around the sun we have a mighty 9 planets, which suggests that planets are jolly common right off the bat.

    There is more evidence - only recently have we had the technology to examine other stars for the existence of planets. And yet already, after just 5 years, we have found 67 planets not of Earthly origin. Given that we can only see the biggest planets as yet, this would suggest that these bodies are phenomenally common, and I feel no hesitation in giving fp a value of 95%.

    Ne=The number of 'Earths' per planetary system. In other words, how many of these planets are in the habitable zone? This is very easy to calculate. In terms of temperature, the habitable zone is from -50 Celsius (The South Pole) to +50 Celsius (Sub Saharan Africa). The temperatures in the solar system range from 200 (Mercury, the hottest) to -200 (Pluto, the coldest). This is a range of 400 degrees, of which habitable is 100. So the habitable zone is 25% of the range out from any star, so therefore, by a process of simple logic, Ne = 25%.

    fl = Percentage of those planets where life develops. This is where we leave uncertainty behind and start to have more of an idea of the figures. Life develops very easily indeed - for it is a simple process of complex forms replicating themselves. Salt, for example, is a form of life, for each layer of a salt crystal creates the next when in solution. It is thought that it is by this process that life first developed. As clays and salt solutions are extremely common on all planets, it is fair to say that this figure is extremely high. But I shall still be prudent and conservative, and pin the figure at 90%.

    fi = Percentage of those planets which develop intelligent life. Given that you have life on a planet, how likely is it that intelligent life will develop? Well, again. I would say that this figure is very high indeed. As life develops by a evolutionary, Darwinian process, and as only the fittest survive, it is clear that any life form more intelligent than another will persevere. There is an inevitable, unstoppable pressure on creatures to become more intelligent. Therefore fi=90%, or thereabouts.

    fc = Fraction of above where technology develops.This one is easy. All intelligent civilisations develop technology, otherwise they wouldn't be very intelligent now, would they? fc=100%.

    L = Lifetime of these civilisations (years). This one is more difficult. The only thing that can destroy a civilisation is another civilisation. Otherwise, they are immortal. Given that conflict is extremely common, but that total annihilation is not, we can safely estimate that L = 1 Billion or so, if not more.

    Multiplying all these numbers together, we see that N = 1,921,826 civilisations active now in our galaxy.

    And there is more: Our galaxy is only 120,000 light years across. So the nearest civilisation to us will be in the nearest star to us, or possibly even in our own solar system - such as Jupiter or Venus.

    This is the greatest threat Mankind has ever faced.

    What happens when one civilisation meets another? Well, if one of the civilisations is more advanced that the other, then the inferior is completely subsumed. This is a law of nature. It is happening now - USian culture is flooding the world, not through force of arms, but through sheer superiority. The effects of even meeting a more advanced alien civilisation, even a supposedly friendly one, would be unthinkable. It is that end that certain far sighted organisations are already working to defend us against.

    It is clear to me that the USA must increase hugely its space weapons programme, in order to defend the Human Race from the impending alien cultural imperialism. They will start insidiously, with simple prime numbers bleeped through space from far off stars, and then progress to music and plays, novels and TV programs - these hallmarks of what it is to be human will be supplanted by alien ideas.

    I hope that with this revelation the USA does the right thing. When we hear those prime numbers being broadcast, we must switch our radio off and ignore the impure transmissions from far away. China succeeded in this aim when it turned away the Europeans, and retained their culture, where the Japanese did not (something we must be wary of). We should learn from these old, noble civilisations and do the same ourselves.

    Curiosity can result in the death of identity - it is this we must fight to avoid.

  • Mathematics (Score:5, Interesting)

    by Dexter77 ( 442723 ) on Saturday January 04, 2003 @01:34PM (#5014533)
    A theory I once heard:

    Universe is about 15 000 000 000 years old. If habitable planets are common then there has to be much older races than we are. Let's say that one of those races is capable of space traveling and it takes 1000 years for that race to spread from planet to another. If they were 1 000 000 years older than us then they would've spread around the universe to 2^1000 planets. Even if it took 10 000 years to populate a planet after reaching one, they would have populated 2^100 planets. Now think about a race that would've been around for a 1 000 000 000 years. They should've populated every habitable planet in the universe.

    I can't remember the name of this theory, but please tell me if you do.

    • The Fermi Paradox (Score:3, Informative)

      by dexter riley ( 556126 )
      i.e. If there are aliens, why the heck haven't they colonized the earth by now?

      Here's a link. [faqs.org]

      But do fleas wonder if there is life on other dogs?
    • I've also heard a religous fanatic theory that attempts to disprove evolution because the probability for change is so incredibly small that the likelihood of going from amoeba to Man in just 3.5 billion years (I believe that's when the first signs of single-celled organisms first creep up) is equally small. An adaptive change being really, really rare, and the sudden environmental changes that would needed for accelerated adaptation (to cram what should be (for the sake of argument) 50 billion years of evolution into 3.5) also being quite rare.

      These probability assessments likely have some merit, but I think they demand closer inspection of all variables involved. For instance, without an entire mapping of the evolutionary tree, we cannot see the emergence off a predatory species that suddenly kills of most of another species, of which the survivors attribute their good fortune to evolution.

    • Re:Mathematics (Score:4, Insightful)

      by spike hay ( 534165 ) <`blu_ice' `at' `violate.me.uk'> on Saturday January 04, 2003 @02:24PM (#5014815) Homepage
      They should've populated every habitable planet in the universe.
      One thing that I've never understood in scifi is that the aliens are always quite a bit like us. They are explorers, and they are interested in conquest, philosophy, etc. One thing we have to remember is that life on other planets is likely to be vastly, vastly different from life on Earth. On earth, we share a great deal of genes with our most distant cousins. Alien life will be completely different.

      There will of course, be some parallel evolution on other planets. For example, fish on other worlds will always be streamlined and usually have the same kinds of fins as earth fish. Most large animal on other planets will have four legs. If technical civilizations evolved from these four legged creatures, they would probably be bipedal. Anyway, intelligent alien life probably won't share the same drive to explore or even advance, that we do. Many intelligent aliens will be perfectly content to live a primitive lifestyle, most likely. Many may even eliminate themselves with powerful weapons.

    • Mainfold: Space (Score:4, Interesting)

      by Genady ( 27988 ) <`gary.rogers' `at' `mac.com'> on Saturday January 04, 2003 @02:34PM (#5014867)
      Read Manifold: Space [amazon.com] by Baxter. There's some very good theory in there that basically states that "life will find a way" It's like a cancer, if there's any concievable way for it to flourish it will.

      The other big idea is that in order for intelligent life to exist for more than an intergalactic blink of an eye it has to expand to other star systems, eventually it needs to expand at a rate faster then the speed of light or it dies, basically making the foot print of intelligent life look like a circle. The outer fringes are where life it, the center is where intelligent life can't exist for lack of natural resources.

      Anyway, it's a good read with some interesting ideas.
    • Let's say that one of those races is capable of space traveling and it takes 1000 years for that race to spread from planet to another. If they were 1 000 000 years older than us then they would've spread around the universe to 2^1000 planets

      Well, unfortunately this calculation assumes that for each of your colonized planets, there are always 2 new ones within 1000 years. This gives you exponential growth for the number of known systems, but in reality the growth is only quadratic, like the surface of an expanding sphere around the starting place.

      For example, if we could go to Alpha Centauri in 1000 years (probably not completely unrealisitc) this theory would state that we would reach 2^1000 planets in a million years - this is more planets than in the known universe. But in reality, after one million years we would have gone about 4LY (distance to Alpha Centauri)*1000=4,000 LY from Earth. This will only reach a small portion of our own galaxy, the Milky Way, which is 100,000 LY across.

      Tor
      • but in reality the growth is only quadratic,

        The number of accessible worlds grows like the cube of the distance (well, until you have made it through the thickness of the galactic disk at least).

    • Re:Mathematics (Score:5, Interesting)

      by sunspot42 ( 455706 ) on Saturday January 04, 2003 @04:28PM (#5015405)
      There are lots of reasons why we might not have detected alien civilizations (yet) - even if they're quite common throughout the universe - let alone seen any evidence of their colonization. I can briefly list a dozen reasons right off the top of my head:

      1) Gamma ray bursts. Until relatively recently in the history of our universe - perhaps up until 500 million years ago - radiation from gamma ray bursts (and supernovae, for that matter) was routinely sterilizing the surfaces of most planets within our galaxy and every other fair-sized galaxy. It took 4.5 billion years for intelligent life capable of interstellar communication and interplanetary travel to evolve here on our planet. Assuming a roughly similar evolutionary pace on other worlds, there might just now be a handful of intelligent species coming into being throughout this galaxy (and others, for that matter).

      2) We're the first civilization to evolve in our galaxy. Unlikely, but someone's gotta be it. Whether or not we could be the first depends in large part on how rare advanced life forms are in our galaxy - a question we may have the answer to within our lifetimes, thanks to advanced space telescopes like the Terrestrial Planet Finder and its successors. If it turns out life on terrestrial planets is exceedingly rare - on the order of only a few dozen planets in our galaxy - then we very well could be the first intelligent species to evolve.

      3) Intelligence is common. Civilization is less common. Technology is vanishingly rare. Remember, in order to colonize the galaxy - or even be detected by a project like SETI - you have to have more than intelligence. You even need more than civilization. SETI is really the search for extraterrestrial *technology*. Space colonization requires technology. For whatever reason, perhaps few intelligent lifeforms make the leap to civilization, and fewer still make the leap to a technological civilization.

      4) Technological civilizations invariably wipe themselves out, or are wiped out by natural processes before they can begin interstellar colonization. A sobering proposition, but certainly one that's supported by our own civilization's close encounters with destruction (the Black Plague, the Tunguska event, WWI, WWII, the Cuban Missile Crisis, Ebola, AIDS, terrorists with bioweapons . . .).

      5) The technology to engage in interstellar travel might be common, and technological civilizations might endure long enough to make such efforts practical. However, that same technology makes such expensive (and risky) undertakings unappealing. Why spend 50 years traveling to the nearest inhabitable planet? You might send out probes - or build larger telescopes - to observe other worlds, but you can simulate their environments and explore them from the comfort of your living room via virtual reality. If you could go on safari in your living room, would you sit in a cramped airplane seat for 20 hours flying to Africa?

      6) Technological civilizations eventually die not with a bang, but with a whimper. We see evidence of this happening already in Europe, where population growth comes only via immigrants. But what happens if the rest of the world reaches the technological and social advancement Europe has attained? Populations may begin to slowly decline worldwide. Without population pressure, there's no reason to colonize new territory here on Earth, let alone other planets. Indeed, you couldn't spare the human capital.

      7) Interstellar travel is impossible, for some currently unknown reason. Perhaps there are giant invisible particles between the stars - they could even be the source of that missing mass we hear so much about - that an unlucky spacecraft could slam into, instantly halting its journey to a nearby star. This is admittedly an unlikely proposition, but we'd be foolish to think we know everything about the feasibility of interstellar travel. Perhaps it's impossible regardless of your level of technological advancement - hence, no alien colonies scattered about the galaxy.

      8) They're already here. This could either take the form of X-Files-style shenanigans, or more benevolent intervention (think Gary Seven from that old Star Trek episode "Assignment: Earth"). Or perhaps only their probes are here, either so microscopic we don't detect them, or somehow disguised as ordinary objects (or creatures - this would go a long way towards explaining the behavior of housecats).

      9) They've all been wiped out by a malevolent alien über-civilization - one that could be on its way to eliminate us. Such villains are a sci-fi staple (War of the Worlds, Independence Day, The Borg), and one we've been foolish to so easily dismiss, especially in light of the silence that greets us from the heavens. There has to be some reason why alien technological civilizations are so rare, and this explanation is as valid as any other in light of the current evidence. Our radio broadcasts already reach out over 100 light-years, starting with the first primitive Morse Code transmissions from over a century ago. We've even deliberately (and foolishly) transmitted high power radio signals directly into space, in various attempts to announce our presence to interstellar listeners ("an open invitation to alien invasion" as the good Doctor on Britain's Doctor Who once wisely pegged it). How long we have before the day of reckoning depends on how close their nearest listening station is, and whether or not they've perfected a means of hyperlight travel. Assuming their nearest detector is 100 light years away, they've just become aware of our presence. Assuming they're limited to sublight travel, we've got another century before they - or some planet-busting weapon - arrives to deal with this latest disease outbreak in their galaxy.

      If you find this scenario unlikely, consider how you'd react to an anthill suddenly springing up in your living room.

      10) They're all hiding from possible über-civilizations (or each other). This certainly wouldn't be a stupid position to adopt, given the consequences of such an encounter. If you don't know what's out in the forest, you'd do well to keep quiet. And once you do know what's out there, you might have an even better reason to keep quiet. Technological civilizations might go completely underground, perhaps relocating themselves to an unspoiled nearby planet and burrowing deep beneath the surface in an effort to completely hide themselves from alien invaders - at least, until they feel they have the technology to resist any such invasion. Perhaps those gamma ray bursts aren't always natural phenomena at all - maybe they're sometimes the visible artifacts of colossal alien wars.

      11) Maybe they're all hiding from us. Perhaps there are no evil overlord über-civilizations. Maybe a federation of benevolent civilizations rules over our galaxy, perhaps after uniting to defeat less enlightened powers. Perhaps these enlightened powers possess the equivalent of Star Trek's Prime Directive, a strictly hands-off policy regarding lesser civilizations. We could dwell in a kind of interstellar game reserve, one that's off limits to alien intrusion. If so, we might never detect our superiors - at least, not for thousands of years, until we possess the technology to go out and meet them face-to-face. It's a comforting thought, but I wouldn't bet my life on it.

      12) Maybe they aren't deliberately hiding from us. Perhaps we're surrounded by interstellar homebodies, but just can't hear them because they don't use radio to communicate. For whatever reason - simulations, interstellar obstacles, declining populations - they don't travel or colonize (much), so we don't physically encounter them or their artifacts, and their communications technology either doesn't involve radio (maybe they use some form of quantum communications), or utilizes radio in a way that sounds like static to our receivers. Of course, you'd think they'd detect our signals and issue some kind of reply, but they'd have to be within about 50 light years in order for that to be possible. Perhaps there's simply nobody that nearby. Entirely possible, if alien civilizations don't travel much.

      Even if you assume there are thousands of technological alien civilizations in this galaxy, if they only communicated with our form of radio for 100 to 200 years of their existence, it's possible there's nobody using our form of radio at the moment anywhere in the galaxy apart from us. Meanwhile, the galaxy is so vast, even with thousands of civilizations there might not be anybody listening within 500 light years of the Earth.

      Anyhow, it's way too early to say why we haven't been contacted, let alone visited, by alien intelligences. We simply don't have enough evidence. Some of the possible explanations are certainly unsettling, though.

  • Moon (Score:5, Interesting)

    by tsa ( 15680 ) on Saturday January 04, 2003 @01:37PM (#5014551) Homepage
    I wonder what life will look like on planets that don't have a moon like ours. The moon is very important in keeping the earth's axis ariented in the same position with regard to the sun. Without the moon, earth's axis could tilt so that one of the poles can be positioned towards the sun, thereby illuminating one side of the earth constantly while keeping the other side in the dark. If life can evolve on such a planet I would very much like to see what it looks like.
    • Without the moon, earth's axis could tilt so that one of the poles can be positioned towards the sun, thereby illuminating one side of the earth constantly while keeping the other side in the dark. If life can evolve on such a planet I would very much like to see what it looks like.

      Star Trek Nemesis is still playing in a theatre near you. :)

    • They would probably look like the Remans from ST: Nemesis since that's the condition you described on Remus.

  • Possibly an underestimate (Score:3, Interesting)

    by imnoteddy ( 568836 ) on Saturday January 04, 2003 @01:37PM (#5014552)

    According to the article they were looking for the possibility of Earth-like planets in indendent orbits around stars. They weren't looking at the possibility of planets (moons) in orbit around gas giants. There is speculation reported here [cnn.com] that Jupiter's moons Callisto, Ganymede and Europa have subsurface oceans which could support life.

    Adding moons of gas giants could raise the percentage of systems with Earth-like planets to higher than the 25 percent reported.

  • We don't know squat! (Score:3, Interesting)

    by mark-t ( 151149 ) <markt@nerdf[ ].com ['lat' in gap]> on Saturday January 04, 2003 @01:38PM (#5014559) Journal
    • One time they're saying that habitable planets are almost everywhere.
    • Next time they're saying that the conditions required for habitability are too narrow -- there is not enough scope to allow for the likelihood of very many habitable planets.
    • Next time they're saying that since it does appear that many star systems have planets, there should be several hundred million habitable planets in our galaxy alone
    • Next time they're saying that habitable planets have to reside in what appear to be "calm" patches of the galaxy, where the gravitational influences of multiple stars upon an object is below some threshold, an uncommon proposition, at best -- extremely rare being more likely.
    • Now they're saying that habitable planets may be everywhere again.

    Bullshit! Why don't they just F***'in' admit it... we have NO idea what's out there and we're never going to know, or even have a bloody friggen clue, until we go out there ourselves (or at least SEND out a probe) -- it's plainly obvious that trying to extrapolate something meaningful from remotely observed phenomena alone is just not useful!

    (end of rant)


    • I suggest that we send out more than one probe.

    • Pop quiz, hotshot: you're gonna send a probe. Based on your remotely observed phenomena, where are you going to send the probe to? The most likely place, right?

      All we're seeing here is the scientific community "thinking out loud"--brainstorming, in a sense--about what the most likely places might be, given the limited (but growing!) body of information currently available.

      (end of counter-rant)
    • You're acting like there's only one group of scientists out there, and they are constantly changing their minds. Did it ever occur to you that there might actually be more than one group of scientists, and they might have differing thoughts about the habitability of extrasolar planets? Astonishing, I know, but there's not just one uniform block of "scientists" who all believe the same thing. Those five different views you just listed are all from completely different people.
      • That's my point, actually... if different people can come to such radically different conclusions from the same obervations, it's evident that we probably can't reliably conclude ANYTHING from the observations we've made thus far. We just won't know until we get there (or aliens arrive here). I could have a lot more respect for a scientist who will admit that anything more than that is nothing but guesswork, and not so different from the fantasies dreamed up by SF writers.

        Beside, if we ever do meet aliens, then we'll know they exist... and if we don't ever meet aliens, does it really matter if they exist or not?

  • The Most Important Considerations (Score:4, Funny)

    by Gigantic1 ( 630697 ) on Saturday January 04, 2003 @01:40PM (#5014569)
    Although the prospect of other stars that are capabale of supporting Earth-like planets is facinating, we need to ask some fundamental questions: 1. Do they also host responsible civilizations; 2. If not, then are these civilizations developing Weapons of Mass Destructrion? If so, then it is imperative that we begin preparations immediatly. If not, then it is still our moral obligation to eventually begin the design and test of Planet-Cracking Weapons to neutralize whatever violent civilizations we may encounter. In the meantime, I believe we should also implement a 7/24/365 inter-steller broadcast of our intentions so that civilizations who could cause potential conflict will "get the message": "Dont F__K with Earth". Specifically, I reccomend that we immediatly begin to repeatedly broadcast the "Planet Cracking" scene in "Star Wars"; although we don't have this technology yet - the Death Star, the aliens won't know that: it will be an adequate bluff.
  • Based on the sometimes catastrophic consequences of British (and lesser so) American foreign policy on Earth, we better sort out our space exploration strategy sooner, rather than later. Our questionable motives for visits to other lands here on Earth have caused much grief and loss of dignity here due to our 'Western' arrogance. Now we have developed the capability to destroy ourselves (and then some), we will need to be very tactful if we do touch base with another intelligent race. Chances are, no matter our technical achievements, they will have the power to stomp on us like ants if we put a foot wrong using their weapons of mass (planetry) destruction.

    So, slash dotters, is it not time that Earth laid down the foundation for some Prime Directives?

    Engage! - With etiquette!

  • Okay, besides the fact that this is the new scientist, the weekly world news of scientific discovery, that doesn't make this theory of prolific life in the universe any less valid than the theory of no other life in the universe.

    Life on earth is prolific. There are no enviornments on earth which humanity has yet to explore which do not contain some form of life. Heck we've even disocvered complex ecosystems at the bottom of the ocean sustaining themselves no through the sun's energy but from chemical processes.

    One day humanity is going to look back on the idea that earth is it and think of it in the same frame of mind that we now think of the age old theory that the earth is flat and you can fall off the edge.

    When we do find alien life it may not resemble anything we know, but it will be everywhere.
  • Just that, it's nice to know that they may be out there, but we haven't the technology to make it to our nearest neighboring star (Alpha Centari, a mere 4.3 light-years away). Long story short, better telescopes and math are nice, but we need a lightspeed capable drive.
    • I support the Palestinians. So would you if you cared to open your eyes> [electronicintifada.net]

      Interesting. But the last time I opened my eyes, the Palestinians were sending children armed with suicide bombs to kill civilians. The more clear-sighted I get, the less I support things like that.

      You are, of course, free to interpret my position as an endorsement of the U.S./Israeli policies, but I wouldn't recommend it.

  • What would deal a bigger blow to these sorry-assed religions than meeting up with planetfulls of other intelligent beings, none of whom have heard of Allah, Yahweh, etc., and we haven't heard of their True Religions, Karlax, Vronontia, Mooolawaei....

    Well what do you know, there's hope for the world yet!

  • Link to Original Paper (Score:4, Informative)

    by Alien54 ( 180860 ) on Saturday January 04, 2003 @01:55PM (#5014658) Journal
    Here is the link to the Original Paper:

    http://arxiv.org/abs/astro-ph/0210006 [arxiv.org]

    Note that you can download the full original in PDF, Postscript, or other scientific formats. The PDF is about a half meg in size. and is about 38 pages long.

  • I'm curious if the fine folk at SETI have already gotten data from those 25%, or have they had a plan of where/when to get get data and they're sticking to it regardless of latest findings? I'd love to know that my SET@Home client is processing data from what may be a more likely location.
  • Did you not read the recent disscusion [slashdot.org] about THE rules of relativity?

    Sorry to burst that bubble... ;)
  • The study doesn't take into account the moons of gas giants. It either Jupiter or Saturn were "in the goldilocks zone" (not too hot, not too cold!), then several of their moons (Europa, Calisto, etc) would be very Earth-like. Most of the studied systems have gas giants in close-in Earth-like orbits... Maybe most stars in our neighborhood have habitable planets.
  • It seems to me that, for some reason, scientists are unwilling to accept the possibility that life can exist in places that don't appear to "habitable" based on the examples of life found on this planet, Earth. For example, recently it was mentioned that the Venusian atmosphere may contain bacterial life of some sort, due to the presence of certain gases that simply shouldn't be there. This comes as a shock, since Venus is so "uninhabitable" by our Earthly definition of that word.

    Life on Earth is very diverse, and we have only begun to understand it. Recently life was discovered in some thermal vents deep under the Earth, were it was thought impossible for anything to survive. About a year ago, a new type of insect was discovered in Central Park. Doesn't this just sort of prove that we humans have absolutely no authority over what is "habitable" on a galactic scale, which could prove to be infinitely more diverse? Isn't it at all possible that there are forms of life out there so different than what we know here, that it could fill our minds with awe, and freeze our souls with terror?

    Lastly, I'd like to add that this is good news for future humans, if we ever decide to colonize other worlds.

  • Connect the dots (Score:3, Funny)

    by grumpygrodyguy ( 603716 ) on Saturday January 04, 2003 @02:49PM (#5014940)
    One in four of the planetary systems identified to date outside the Solar System are capable of harbouring other Earths, say astrophysicists, a much higher proportion than anyone expected.

    Is it me or does anyone see the connection? Those of us who've played the fabled "Master of Orion" series(Civ in space) are well aware that on average 1 in every 4 planets are hospitable to indigenous life. (You can teraform planets to colonize them, but 1 in 4 are naturally sustaining)

    So apparently the game designers knew about this research well before it was published(1994). Or the scientific community is "broadening" its scope to include data from computer games. I'm more inclined to believe the latter, as game designers usually don't have time to engage in bio-astronomy on the side.

  • There's a large difference...... (Score:3, Interesting)

    by SETIGuy ( 33768 ) on Saturday January 04, 2003 @04:28PM (#5015404) Homepage
    There's a large difference between "capable of having planet with a stable orbit in the habitable zone" and "having an earthlike planet with a stable orbit in the habitable zone."

    Don't get me wrong, I'm a big fan of looking for extraterrestrial life and earthlike planets. (Who would have guessed?) That there are stable orbits in the habitable zone of many stars is not a surprise. It really says very little about the number of earthlike planets out there.

    I'm not the biggest fan of splashy press releases for unsurprising results. (I think the "more than anyone expected" comment is well overstated.) But it's AAS meeting time, so we'll be seeing a few of those this week. The usual ones are:

    • the best evidence ever for existence of black holes.
    • it looks like life could be common in the universe, but we still have no evidence of this.
    • more planets have been found.
    • the first time "blank" has been observed, where "blank" is something that has been announced as being observed for the "first time" at the previous 10 AAS meetings.
    • a controversial mars "result" that will be argued about for years.
    • look at the pretty pictures a half billion dollar space mission can give you.
    These are the ones you will hear about because we astronomers tend to think that this is all the press would be interested in hearing about. Maybe we're right, maybe we're not. At any rate, AAS meetings are a good time to think about whether the way we sell science to the public is the best way. Any suggestions?

    Hidden among these press conferences will be one surprising result that is wrong, one surprising result that is correct and interesting, and the correction of a surprising result released at the previous meeting. And there will be a lot of interesting research presented by people who don't schedule press conferences. It will, for the most part, be ignored by the press.

  • a) there is intelligent life out there. Maybe not in this post, but out there, yes.
    b) they know we're here, but they don't care. It's as if you discovered a bee hive in your backyard. Are you going to go over and bug them or just let them go about their business? Not unless they start heading towards your house..
    c) intelligent life obviously live on planets, proably much like Earth.

    I wonder if 300 years from now, the concept of having to constantly prove that life in outer space exists is as stupid as once believing the Earth was flat.
  • Caught a great book once called "The Ambidextrous Universe" that had a chapter on alien life and the forms it would take. (Book itself was about symmetry and asymmetry in nature - very cool.) It made the argument that if we encounter non-plantlike alien life it will likely be recognizable and that the basic 'animal' forms on earth are likely universal. Argument went thusly:

    If a creature is motile, then symmetry dictates basics. There is rarely any functional difference between left and right but there is a difference between forward and backward. So animals would likely have a front and a back, but would be symmetrical along a dorsal axis. (There are exceptions to this in nature, creatures with a spiral morphology like the conch, or creatures like the fiddler crab, but these are rare exceptions.) Since front is generally more emphasized than back, sensory organs are more likely to be collected near the front. Further, if the animal feeds (which seems likely) then it seems logical that sensory organs would be concentrated around the feeding orifice. Further, since minimal distance between sensory organs and the 'brain' (assuming aliens have brains) is more efficient for reacting faster to the environment, it seems likely that the mouth and forward facing sensory organs would be concentrated on a head-analog. (A face, basically.)

    The argument wasn't claiming to be definitive, but rather that the recognizable forms of symmetry, faces set on the front of heads, heads at the front of bodies (and set high up to elevate the sensory organs to extend range) have a logic to them that would likely be repeated.

  • Too bad there's not more technical details... (Score:3, Informative)

    by shimmin ( 469139 ) on Saturday January 04, 2003 @06:26PM (#5015914) Journal
    ... because what constitutes a "stable" orbit is a matter of some debate.

    You only need to play around with an orbital mechanics simulator like the one here [geocities.com] a little bit to convince yourself that the long-term stability of an orbital system with more than 2 elements is a rather chaotic matter.

    So I'm curious how long they deemed an orbit had to stay within what boundaries to deem it "stable." For example, for our own system, it appears that most of the planets are likely to remain close to their present orbits until the Sun goes red giant, but Pluto's orbit is difficult to predict past about 3 billion years or so, according to some simulations.

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