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Space Science

30 Billion Earth Sized Planets? 58

Posted by michael from the spaceward-ho dept.
Tha_Chaotic_1 writes "The BBC is running a story about a prediction that there are around 30 billion earthlike planets in the universe. This comes following the discovery of the 100th gas giant outside our solar system. Optimistic?"
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30 Billion Earth Sized Planets? More

30 Billion Earth Sized Planets?

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  • Before we get all optomistic, how many light years away are the nearest four of these planets?

    • Re:How Far Away? (Score:3, Interesting)

      by capt.Hij ( 318203 )
      With the new world, astronomers say that they have just about finished surveying all the Sun-like stars out to a distance of 100 light-years from Earth.

      Looks like they *think* that they've poked around in a 100 light year radius of earth. Given the extremely poor precision in which distances are measured this may be a bit optimistic.

      Also from the article:
      And if stellar statistics gathered in our local region of space are applied to our galaxy of 300 billion stars, then there may be 30 billion Jupiter-like worlds and perhaps as many Earth-like worlds as well.

      Since our universe is not uniform this may be an abuse of statistics. They've only looked at one very small corner. This is a heck of a Monte-Carlo simulation, though!

  • gamma-ray emissions (Score:3, Interesting)

    by bofh31337 ( 521771 ) <bofh31337@gmai[ ]om ['l.c' in gap]> on Tuesday July 02, 2002 @08:24AM (#3806563) Journal
    I think this number is a bit high. I'm not sure they've taken into account that solar systems too close to the center of the galaxy due to the "galactic doughnut" effect. Anything to close to the center of the galaxy, in the doughnut hole, would not be habitable due to excess bombardment of gamma-rays.

    • Re:gamma-ray emissions (Score:3, Insightful)

      by Passman ( 6129 )
      What you mean is that it would not be habitable by us.

      One of the things that life has shown is it's annoying ability to survive where it should not be. Consider the bottom of the Atlantic Ocean: no sunlight, tempratures hot enough to boil us alive, heavy metals and unique compounds forming a soup toxic to life as we know it. Yet life teems there, hundreds of species of plants and animals.

      If life can adapt to that, why not to a few gamma rays?
      • If life can adapt to that, why not to a few gamma rays?

        Poking into the realm of science fiction, one would have to presume one of two things for this to happen. Either these life forms would have some sort of natural protection from such radiation or have developed some technology that protects them. Or their life is based on something other than carbon (silicon?). The reason for this is that all carbon based life is easily damaged by high energy light waves. Indeed, most non-metals tend to break down their molecular bonds when exposed to gamma rays. Either way, despite the tenacity of life, it would require a large leap of faith to assume that this is the case.

        • Poking into the realm of science fiction, one would have to presume one of two things for this to happen. Either these life forms would have some sort of natural protection from such radiation or have developed some technology that protects them. Or their life is based on something other than carbon (silicon?). The reason for this is that all carbon based life is easily damaged by high energy light waves. Indeed, most non-metals tend to break down their molecular bonds when exposed to gamma rays. Either way, despite the tenacity of life, it would require a large leap of faith to assume that this is the case.

          Actually, since gamma radiation is so high-energy, it would be an ideal food. Think living metal plants absorbing gamma radiation instead of light radiation. Think metal "herbavores" eating the metal plants. Think metal "carnivores" eating the metal herbavores. Think sentient bipedal metal "omnivores" eating metal fast food, trying to estimate the density of life in the galaxy, discounting the idea of life in the outer arms due to the lack of an abundant energy source.

          • Think living metal plants absorbing gamma radiation instead of light radiation.

            Unfortunately, there can be no metal based organisms. Only silicon and carbon have rich enough chemistry.
          • When life absorbs gamma radiation, that life is generally destroyed. The harmful mutations that exposure to gamma sometimes produces are basically a mild case of destruction.

            Before anyone comments on consequent high mutation rates and speculates on rapid adaptation, it's worth pointing out that increasing the mutation rate increases the organism's genetic burden, or in other words reduces the organism's survivability. High replacement rates entail a high `genetic death' rate for the species.

            Life consists of highly specific, nested, complex structures. Think of a lunar rover [nasa.gov] built from Lego [lego.com] bricks [looks like a fabulous place of employment!]. Units like the wheels represent a unique and specific structure by themselves; the whole rover represents a structure of structures. Doing something like bashing a chord or segment out of a wheel not only impairs the wheel's function, it also impairs the entire rover's function. What you're proposing is akin to suggesting that `improving' the rover's structure can be done by subjecting it to higher than normal levels of machinegun fire.
        • Either these life forms would have some sort of natural protection from such radiation or have developed some technology that protects them. Or their life is based on something other than carbon (silicon?).

          i find it amusing that since silicon is in the same family as carbon people point it out to be an element that life could arise from, forgetting that the multiple-bonding ability of C is unique to this element... Anyway most of the reason that gamma rays (and lots of high-energy photons) are dangerous to 99% of us wee little earth-dwelling creatures is because we have not evolved to prevent/repair this damage. if i bash apart a shitload of DNA in one of your pluripotent stem cells what will the cell do? - it's programed to undergo apoptosis (suicide), why?-because it's a (more or less) rare event that your cells acquire genetic damage (to that extent anyway) so it's more evolutionarily advantageous that the few cells that are damaged just die instead of spending the energy for every cell to continually have a plethora of genetic-repair proteins on the stand-by. if we were from a planet where a large percentage of our cells were being damaged continually then it would be more advantageous to have mechanisms by which to repair said damage...

          there was a bacteria discovered a few years ago (this is off the top of my head mind you) that can survive up to 800 rads.

          although it is true that gamma-ray bursts can evaporate an entire world's oceans, but so did meteors continually do so in the early years of dear old earth...

          of course like the 'god arguement' no one can actually 'win' this arguement, but i just thought i could piss farther than you, heh :)

          -tid242

          • i find it amusing that since silicon is in the same family as carbon people point it out to be an element that life could arise from, forgetting that the multiple-bonding ability of C is unique to this element...

            Boron also has a multiple-bonding ability similar to carbon. The major problem for B-based life forms is the relatively low cosmic abundance of the element.

            Silicon per se isn't particularly good for building large and complicated molecules out of, but in combination with oxygen it is excellent. Check out the structure of silicones and, for that matter silicate minerals. The latter frequently include magnesium and/or aluminium for added structural variety.

            Remember, also, that organic chemistry is much more than the chemistry of carbon. C might be the essential element but there are very few molecules of biochemical interest which don't also contain hydrogen and most contain oxygen and/or nitrogen too.

            It's not at all obvious to me that you can't build life-forms out of Si/O/Al/Mg, or out of boron, hydrogen and the first-row elements N, O and F.

            Paul

          • Actually silicon can form multiple bonds, it's just that there large atomic size makes this differcult. I put in Si=Si into SciFinder Scholar (a chemistry database) and got just over 900 matches. While many of these will be repeats, Si double bonds do exist.
      • What you mean is that it would not be habitable by us.

        Yeah, instead of it being inhabited by little green mean, you'd have large muscular green mean with nasty dispositions (unless you happen to be a hot chick in trouble - hmm doesn't that apply to all guys?).

      • Gamma-rays have the anooying tendancy to beak atoms into siny little bits of energy. An intense gamma-ray burst will start transmutting elements into other elements. Even UV radiation has enough energy to ionize molecules. Besides the fact anything producing intense gamma and X ray bursts would tear the shit out of a planet anywhere near it. You need to be less worried about life surviving in one of these environments and just wonder how a planet might survive in these environments. Your planet being whisked off into space from the supernova that caused a gamma-ray burst is going to be a much more difficult problem to deal with than the gamma-rays themselves.

    • it's worse than that (Score:3, Interesting)

      by Tumbleweed ( 3706 )
      There's also a theory that says that you may well need to have at least one gas giant further out from your star to help deflect space schmutz from wiping your species out too early. Since we have 4 very large planets further out from our planet, we've got a lot of gravity wells helping to keep the inner system cleaner than it would normally be. Then again, this may be a rather common configuration - if a star forms and a gas giant forms, then the eddys between the forming star and forming gas giant may just be what turns into a smaller planet. Where's a Wayback Machine when you need one? *sigh*
    • Um, it seems likely that of the 100 systems surveyed, zero of them have habitable planets due to `excess bomardment of' jupiter-sized and larger planets.

      Every single `sol-like' system so far described has a serious spoiler to it like a jupiter-sized planet orbiting about where Mercury is in our system. This doesn't fit any of our theories of planetary formation; if anything it implies that any solid bodies present would be orbiting within that star's corona... like living in a microwave full of flares.

      Even if a solid planet did circle at earth-like distances, there's nothing like a brown dwarf crossing your orbital path to - sooner or later - ruin your whole day.

  • Optimistic? Probably. (Score:2, Interesting)

    by Pembers ( 250842 )

    Especially when you consider that no-one claims to have seen an Earth-sized planet orbiting another star. But then, no-one would claim that meant there were no such planets.

    The figure of 30 billion Earths appears to be extrapolated from two things. One, that the galaxy contains an estimated 300 billion stars. Two, that of about 1,000 stars surveyed, astronomers have detected planets orbiting about 100 of them, or 10%.

    If this holds for the galaxy as a whole, then 30 billion stars have planetary systems. To say that this implies an average of one Earth-sized planet per planetary system sounds like stretching the data. Sure, we have some theories on how planets form, and every new discovery presents much-needed data to test them, but until someone actually detects a planet the size of ours, we have no idea how common they really are.

    • <quote>
      If this holds for the galaxy as a whole, then 30 billion stars have planetary systems. To say that this implies an average of one Earth-sized planet per planetary system sounds like stretching the data.
      </quote>

      Not necessarily. 10% of the surveyed systems contain gas giants. There may very well be many more systems that only have smaller planets. The planets in those systems are still undetectable with our current technology.

      Johnny

    • Re:Optimistic? Probably. (Score:2, Interesting)

      by wom ( 240411 )
      Of these detected planets, _some_ are large gas type planets close to the star, which would preclude there being an earthlike planet there. Our theories are based on a sample space of one, and "wobbles". OTOH, it well could be that there are earthlike planets attached to stars that don't have giants orbiting them. IMHO, there is no reason to make any prediction based on this data.

      PS. Don't confuse "galaxy" with "universe"
      • Our really big gas giants all (both) have planet-sized moons. This may imply likely habitable-sized moons orbiting a Jupiter or larger sized planet. In the case of the really big planets (say, six Jupiters on up) even a `planet' orbiting `too far' out may radiate enough heat to make a moon habitable.

        Since we know next to nothing about other planetary systems, let's speculate freely. What about a planet of, say, ten or twenty Jupiters' mass, with a Saturn-sized `moon' around which a nominally habitable sub-moon orbits. Set the whole array within a multiple star-system (say, an ordinary star with a close-orbiting dense companion).

        The sunsets would be fabulous (`and this clip shows the changing magneto-optical effects from Whitestar in Primary's rings and atmosphere, backlit by the rich hues of Redstar and offset by the brilliant blue orb of Secondary as we orbit past it, all framed by the spectacular Western Ringwall Mountains...'), and the almanacs would be collectors' items, all fourteen volumes of them. (-:

        I like my idea for a planet better than theirs, and as you said, have just as much evidence for it... (-:
    • The number of earthlike planets in the universe is 42. Oh, now it's 41...
  • I thought Lucas was crazy to assume that there could be a galaxy with so many habitable worlds.

  • Universe (Score:4, Insightful)

    by Mt._Honkey ( 514673 ) on Tuesday July 02, 2002 @09:28AM (#3806844)
    Not to nitpick, but is should be noted that the article states that there are probably around 30 billion earth-like planets in our galaxy, not in the whole universe. A significant point, considering that there are around 10 billion large galaxies and 100 billion dwarf galaxies.

    Wow, if there are 30 billion in our galaxy, that would make around 300,000,000,000,000,000,000 earth like planets in the known universe. If 1/10th of those are capable of supporting life (a pessimistic view when you consider that at least one out of four in our solar system is capable, not to mention mars and europa), then that's still 30,000,000,000,000,000,000 planets that can support life. If even 1% of those actually have life, and .1% of those have had intelligent life, that's 300,000,000,000,000 planets that have had intelligent life forms in the known universe. Of course, you have to factor in the time spans involved...

    On a side note, MS word spell checker recognizes europium, but not europa.

    • Re:Universe (Score:3, Funny)

      by p3d0 ( 42270 )
      If 1/10th of those are capable of supporting life (a pessimistic view when you consider that at least one out of four in our solar system is capable, not to mention mars and europa)...
      Try this:

      "If 1/10th of all mammals on Earth have highschool diplomas (a pessimistic view when you consider that at least 2/3 of the mammals in my apartment have diplomas)..."

      See the problem?

      • I see the point, but I still think that it is fine to base assumptions loosely in my case. Our solar system could be privileged (as your apartment is), but I'd bet (I don't know, of course) that it places us within an order of magnitude of the correct answer.

        On a slightly related note, Fermi problems are fun.

  • Further abuses of induction (Score:5, Insightful)

    by ssyladin ( 458003 ) on Tuesday July 02, 2002 @10:09AM (#3807088)
    This article contains so much flawed logic, it boggles the mind. First, [t]he latest find is a gas giant and orbits a Sun-like star 293 light-years away. Though how this relates to a 100 light year sphere around earth confuses me. Second, with about 300 billion stars in our galaxy, there could be about 30 billion planetary systems in the Milky Way alone. While the 300 billion stars is correct, a vast majority of them are on the galatic disk or in the galatic core, where the gravity of the densely packed stars would prevent planet formation according to any currently held theory, except maybe Electric Universe [holoscience.com]. Lastly, most of the exo-solar planets that have been found so far are multiple Jupiter-sized and orbiting so close to the star that it doesn't resemble our solar system, the only one we really know about, making any inferences about the existence of other planets useless and pointless. While 100 exo-solar plants found is a cheer for modern astronomy and a good sign for the likelyhood of ETs, this article uses poor logic to make a bang from a whimper
    • The parent post contains so much flawed logic and bad astronomy, it boggles the mind.

      Though how this relates to a 100 light year sphere around earth confuses me:
      The article is pretty clear that the 100th planet is "symbolic". It's in really big font in a colored box -- you can't miss it! Anyway, it's not this 100th planet that leads to the 30 billion number. It's just a lead in for the article.

      While the 300 billion stars is correct, a vast majority of them are on the galatic disk or in the galatic core, where the gravity of the densely packed stars would prevent planet formation according to any currently held theory.:
      Wow -- that's news to astronomers. We're in the disk, and our sun formed planets, so it can't be that hard!

      most of the exo-solar planets that have been found so far are multiple Jupiter-sized and orbiting so close to the star that it doesn't resemble our solar system, the only one we really know about, making any inferences about the existence of other planets useless and pointless :
      Oh, so knowing how commonly planets form has nothing to do with how many planets are in the galaxy?!? Knowing that 10 percent of stars near us have detectable planets is astonishing: we can only regularly detect these weird "hot Jupiters" right now. This implies that, unless these systems are for some reason much more common than other planetary systems, a substantial fraction of all stars bear planets. In that case, 30 billion is a reasonable guess -- maybe on the low side!

      The final link in the logical chain is provided in the article itself:

      But even in this "biased" survey of giants, the smaller worlds predominate - which makes astronomers think that Earth-like worlds do exist. They may even be as common as Jupiter-sized exoplanets.

      In other words, if you make a histogram of exoplanets sorted by mass, you see that the least-massive ones are the most common. Go to exoplanets.org [exoplanets.org] and see for yourself. So the above caveat that "hot Jupiters" might be more common than other kinds of planets seems unlikely.

      Yes, the author has dumbed down the science to the point where it can be hard to figure out what he's writing about, but that per se doesn't boggle the mind of anyone who reads the science section of any major paper.

  • With 30 billion planets to visit, Star Trek Enterprise will be the longest running series ever!
  • Jeez. That's not too optimistic.

    Considering that there are >100 billion galaxies, each with around 100 billion stars, that just means one earth-like planet for every 300 billion stars or three galaxies.

    This seems like an underestimation to me. I would say more like 1,000,000,000 earth-like planets in every galaxy.

    If half of all stars had planets (a resonable guess), at least a few of these would have stable orbits around orange dwarf stars and have a similar composition to earth.

    Planets with similar size and orbit to earth would most likely develop life. (Planets smaller than earth would have their atmospheres drift off and oceans boil away, like Mars) Bacterial life is most likely quite common in the universe. It developed here on earth and most likely developed on Mars. Any planet with a resonable climate, liquid water, and volcanism (it provides necessary chemicals) will likely develop bacterial life. Volcanism is very common on all larger planets, the habitable zone is large, encompassing three planets (Venus, Earth, and Mars), so planets in habitable zones are undoubtedly very common, and oceans are common. Earth has oceans, Europa does, and Mars used to.

    BTW, Venus really is in the habitable zone. It's very high pressure CO2 atmosphere just creates an extreme greenhouse effect, heating it up hot enough to melt lead. Mars used to have liquid water and more of an atmosphere, which made it warmer. Mars most likely had life.

    Now, more advanced multicellular life is much more rare. First of all, it was three billion years on earth before multicellular life just happened to evolve. So on many planets, bacteria probably just never evolved much farther. Secondly, multicellular animal life is aerobic and needs oxygen. So unless the atmosphere is already oxygen-rich, photosythesizing bacteria would have to develop first.

    Bacterial life is common, multicellular life is much less common. (Maybe occuring 10% of the time that bacterial life does.) Now intelligent life. There might only be 30 billion planets with technical civilizations in the universe. First of all, intelligence has to evolve. When you think about it, life has been around for 3.7 billion years. In that time, modern humans have only been around for about 150,000 years. Of that time, we have only been capable of sending and recieving radio signals in intersteller distances for 40 years. Most likely we will annihilate ourselves with antimatter weapons in the next 10,000 years.

    For a planet with multicellular life, lets say 1 in 10 will develop intelligent life at some point. And probably many of these intelligent creatures won't develop radio. And those that do will probably only have a radio civilization lastling less than 10,000 years.

    So lets see: In our galaxy, 1 in every 100 stars has an earthlike planet. Half of these have life. So 1 in every 200 systems has life. 10% of these have multicellular life, so 1 in 2,000. 10% of these have had intelligent life at some point, 1 in 2,000,000. Say 1 in five of these develop a radio civilization, so 1 in ten million. If radio civilzations last an average of 10,000 years, there is one radio civilization currently for every 5 billion stars. So there may be several in our galaxy. But communicating with them is probably pointless because they would most likely be thousands of lightyears away.
    • I'm starting to disagree on the Venus bullshit. Greenhouse effects simply can't raise temperatures that high, not even with the most extreme conditions.

      Did you know that Venus is actually hotter on the dark side, even though that can't possibly be if it is a greenhouse effect?

      Or that it actually sustaining a net energy loss? That's right, it's bleeding off more heat than it is taking in from our friend, the sun. Explain that.

      Or the fact that its atmosphere is revolving around the planet many times faster than the planet itself is doing.

      Something funky is going on.
      • Greenhouse effects simply can't raise temperatures that high, not even with the most extreme conditions.

        Well, greenhouse and it's proximity to the sun. Venus is at the inner end of the Golidlox zone. With an earth-like atmosphere, I bet temperatures of 150 F would not be uncommon in the tropical zones, and the polar regions would be more like temperate regions on earth. Keep in mind that Venus's atmosphere is over 90 times as dense as the earth's and it is mostly CO2. It also has a very thick cloud layer made of sulfuric acid instead of water that traps in more heat.
        • !@#!@#$#!!!!! God! forgot the closing tag. Reprinted correctly for your reading pleasure:

          Greenhouse effects simply can't raise temperatures that high, not even with the most extreme conditions.

          Well, greenhouse and it's proximity to the sun. Venus is at the inner end of the Golidlox zone. With an earth-like atmosphere, I bet temperatures of 150 F would not be uncommon in the tropical zones, and the polar regions would be more like temperate regions on earth. Keep in mind that Venus's atmosphere is over 90 times as dense as the earth's and it is mostly CO2. It also has a very thick cloud layer made of sulfuric acid instead of water that traps in more heat.
          • Yeh. And how exactly does a planet not so different from earth in density and size, manage to retain an atmosphere that dense? How many thousands of years would it take, before solar winds swept much of it away?

            Besides, thick cloud layers tend to reflect away incoming energy, creating a natural balance to a greenhouse effect. At the rate it's going, you would expect the dumb thing to regulate itself back to something a bit more normal in a matter of a few millenia, wouldn't you?

            Besides, just how efficient is venus's atmosphere at absorbing and trapping heat? It's not what you would call an ideal mixture for such a purpose, is it? (Note: I'm a high school flunky, so this is more of a guess than some expert knowledge).
            • A planet Venus' size can retain that kind of atmosphere with no problem. There have been several probes on venus that have confirmed the dense atmosphere. (The first soviet venus probe was crushed by the extreme pressures on descent)

              Besides, thick cloud layers tend to reflect away incoming energy, creating a natural balance to a greenhouse effect. At the rate it's going, you would expect the dumb thing to regulate itself back to something a bit more normal in a matter of a few millenia, wouldn't you?

              Keep in mind that they are sulfuric acid clouds. More of a dark brown than white. They don't reflect nearly as much as water clouds.
      • A lot of things have happened to Venus that have taken it on a far different evolutionary route than the Earth. Venus has a much more stable atmosphere then the Earth does and the cloud layer extends far higher than Earth's. Where our highest clouds form at around 16km Venus has a cloud layer almost 70km up. That 10km cloud layer is followed by a second layer is from about 56-52km and a third from 52-48km. Below the third and lowest cloud layer is a haze layer that extends down to about 33km. Below that the air is very clear. The atmosphere is also very uniform which steams from Venus' super slow rotation. It takes Venus 243 days to complete a single rotation, where Earth takes 24 hours. Since large weather systems aren't broken up by the high rotation rate they form into one large and very stable weather pattern.

        It takes Venus longer to rotate about its axis than it does to orbit around the Sun. The Sun is held over a single area of the sky for a very long period of time. The only way Venus has to move heat around is by atmospheric convection. The dark side of the planet is bleeding off all the heat absorbed by the Sun as well as heat radiating off the ground.

        It is easy to explain the net energy loss, it has retained much of its formation heat so it likely has a molten metallic core just like the Earth's and has been heated for several billion years by a Sun that is 30% closer. All of that solar radiation has been stored up in the atmosphere. Its internal heat as well as the built up heat from the Sun are going to make it a very nice energy emitter.

        The atmosphere rotates quickly around the planet because of convection. The atmosphere of Venus would be much easier to model than the Earth's. The warm air of the equator is rising in a single massive column from the subsolar point (the place on the planet where the Sun is directly overhead) and falls back down at the poles and towards the night side of the planet. These convection currents cause super high speed jet streams which rotate in the same retrograde manner as the rest of the planet.
      • What really fucks with my head is that a billion years ago venus was resurfaced. The entire crust of the planet melted, resetting the entire geological history of the crust.

        It would have sucked to have been living on venus when that happened...
    • "If radio civilzations last an average of 10,000 years, there is one radio civilization currently for every 5 billion stars."

      Most likely they only transmit narrow-band signals for a century or so before moving on to UWB or something even harder to detect.

      "So there may be several in our galaxy."

      If I am right ours may be the only one sending out easily-detected signals. Interesting question: if each civilization emits a 100 light-year thick shell of narrow-band rf, what are the chances that we are in at least one such shell now?

      "But communicating with them is probably pointless because they would most likely be thousands of lightyears away."

      We find it interesting to study stars at such distances: why not civilizations?

  • Hard to say (Score:3, Insightful)

    by DeadVulcan ( 182139 ) <dead.vulcan@nOspam.pobox.com> on Tuesday July 02, 2002 @12:04PM (#3807809)

    Firstly, to respond to an earlier post, the article did say "billions of Earths in our galaxy," not in the entire universe. It was the very first sentence, for heaven's sake.

    The biggest question in my mind, with regards to this article, however, is the following statement:

    there could be about 30 billion planetary systems in the Milky Way alone; and a great many of these systems are very likely to include Earth-like worlds, say researchers.

    "Say researchers" is a pretty glib way to support such a big statement. Since current planet-finding techniques can only pinpoint gas giants, I suspect we can really have no idea what percentage of planetary systems contain earth-like planets. So it's this logical jump that is really the issue. And the article is a little thin on the explanation of this reasoning.

    Finally, I would say that a figure that's calculated using sound statistical methods is never optimistic nor pessimistic, it's just that, in this case, the margin of error might very well be something on the order of plus or minus 30 billion.

  • I actually really like what they've been able to do with the technology hunting for planets, however, I have to take some issue with this.


    How many earth like planets have they conclusively found? zero. So where the hell do they come up with a statistic such as this? I mean, come on this isn't even small number statistics or taking an educated guess, this is pure guessing. There's no info to back this up. I'm actually involved in science to some degree, but I get a bit miffed when I see headlines like this, when it's a blatant attempt to try and get some notoriety and funding.

  • "The BBC is running a story about a prediction that there are around 30 billion earthlike planets in the universe."

    Make that 30 billion earthlike planets in our _galaxy_. If there are only 30 billion in the universe it's probably pretty lonely around here.
  • about 10% [of stars within 100 light years] have been found to possess planetary systems. So, with about 300 billion stars in our galaxy, there could be about 30 billion planetary systems in the Milky Way alone;

    That calculation doesn't work. Our local environment is likely to be reasonably good for planet formation. Closer to the core and closer to the fringes of our galaxy, planets probably become less frequent.

  • With this many planets, yes, there are bound to be many civilizations which have developed over the millenia. However, it is illogical to assume that they would all be friendly. If you see a nice looking crocodile in a pool, do you assume it's friendly and jump in? Take a look at the animal kingdom of our own world -- quite a bit of killing going on. In many ways our own civilization is worse in that we don't just kill for food, some of us kill for pleasure. The SETI program is going to get us all killed / eaten / forced to build some big laser pointing toward the sky.
  • Despite criticism that the estimates are too high, due to lower densities elsewhere in the galaxy, I suspect 10% is low for our region, I would guess actual planetary densities to be at 50-90 percent or higher. Remember that the 10% are only confirmed planetary systems nearby. This DOESN'T say the remaining 90% don't have planets, just that we haven't detected them with our relatively crude methods so far.

    This is great news for SETI -- it was only a couple of decades ago we had no idea whether planetary systems were relatively common or not. In fact there was a camp predicting planets to be extemely rare. I guess they have mutated into the "Rare Earth" crowd, and become more specific :-)

  • Intelligent life would be dotted in time (throughout billions of years) as much as in space. Even long surviving species would be miniscule relative to the 10 plus ?? billion years of the galaxy. Even if such lucky planets have multiple extinctions and can repeat the occurance of intelligent life, the odds improve only a bit. What percentage of all such intelligent life is around right now in our blink of time ?. If our window of observational and communication interest is say some 5 thousand years, then out of a snapshot of 5 billion years of cosmic life, we've reduced the likelyhood of current intelligent life elsewhere in our galaxy by a million or so (give or take a zero). Time is as much a distance as space.
  • The discover of Jupitor-like planets is, in part, so exciting because Jupitor-like plantes are necessary to suck up all the cosmic junk floating through the solar system. (Disclaimer: being a physicist, I have heard this first hand from real astrophysicists I trust - obviously they could have miscalculated).

    Cheers,

    G. G. Wood

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