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Should We Expect Other Earth-like Planets At All?

The views expressed are those of the author and are not necessarily those of Scientific American.

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Earth-like? Or not.... (Image:PHL @ UPR Arecibo, ESA/Hubble, NASA)

This year has been a spectacular one for exoplanets. New discoveries and new insights have truly pushed the gateway to other worlds even further open.



In the past 12 months we’ve gained increasingly good statistics on the incredible abundance of planets around other stars and their multiplicity. We also finally seem to have evidence that our neighboring star Alpha Centauri B does indeed harbor at least one world. It is by any set of standards, a great haul.

But I continue to be a bugged by the claims of ‘habitable’ worlds and ‘Earth-like planets’ that seem to beset many scientific announcements (including I’m ashamed to say my own). In the spirit of closing out the passage of our 4,500,000,000 th or so orbit around the Sun I thought I’d try to set the record straight, because I think we have so much more to look forward to than simply finding ‘another Earth’.

First, when press releases state that a ‘habitable’ world may have been found, the truth is far more complex. Astronomers and astrobiologists tend to use the term habitable as a shorthand for the presence of liquid water on a planetary surface, implying a range of temperatures between the freezing and boiling point of water. But this also requires a surface atmospheric pressure high enough for water to exist as a liquid without boiling off to vapor, and an atmosphere will alter the transfer of radiation to and from the surface – often by way of a greenhouse effect.

And this is just the beginning. By this simple criterion even the Earth is only partially habitable – about 85% of its area remains amenable to liquid water over a year  (a fact that my colleagues Dave Spiegel, Kristen Menou and I reiterated a few years ago). So strictly speaking ‘habitable’ includes a range of environments that we would find appallingly hostile, including high-pressure, high-temperature climates and those in a sub-arctic category with thin atmospheres.

Sorry, but you're total conjecture (Credit: ESO)

The problem with the newly proclaimed habitable, or even potentially habitable exoplanets of 2012, is that not only do we at present have absolutely no information on the presence or absence of water or an atmosphere, we also have absolutely no idea (beyond informed guesses) about their geophysical history or present state. Geophysics is the dirty little secret here. On Earth the long-term (read millions of years) stability of the Earth’s surface environment close to the ‘habitable’ state is a direct consequence of geophysical re-cycling, the so-called Carbon-Silicate Cycle. Or to put this more crudely, no volcanism or tectonics, and you get no temperate climate.

This does not mean that some of them don’t hit the sweet spot, but it’s horrendously premature to say so.

Which gets us to the other point, the cavalier use of the phrase ‘Earth-like’. Utterance of this can evoke all sorts of images. It may make us think of oceans, beaches, mountains, deserts, forests, fluffy clouds, fluffy bunnies, warm summers, snowy winters, the local pub, or the fabulous hubbub of the local souk.

But this is typically far from the meaning attached by scientists. It can simply indicate a planet with a rocky surface, rather than a world with a thick gaseous envelope. It can mean a world that is roughly the same mass and density as Earth. It can mean a planet orbiting a star like the Sun. Or it can just mean that we got bored of saying things like ‘a two-Earth mass object in a close to circular orbit around a roughly 4 billion year old main-sequence star that is similar in mass to the Sun.’

Although at some level this is purely to do with semantics I think it’s important to consider. What I believe we really mean when we say ‘Earth-like’ is that a planet is Earth equivalent. That is to say that while the planet might feel completely alien to human senses it nonetheless matches many of the same physical and chemical characteristics of Earth. It’s a bit like renting a car at an airport where you’ve reserved the open top red sports-car, only to be told that they’ve run out but you can have ‘an equivalent’ vehicle. It’ll have four wheels, an engine, and yes you can wind the windows all the way down if you’d like.

And this is critical because one thing we have learned about exoplanets in 2012 is that they are remarkably diverse, and that the configuration and contents of our solar system are somewhat (only somewhat) unusual. For example, none of our planetary sisters belong to what may be the most numerous category of worlds – objects with masses between that of the Earth and that of Neptune. There’s an absolute load of those out there, but none here.

Our system is also relatively spread out, it is increasingly apparent that the universe likes to build compact orbital architectures of numerous planets with orbital periods of days to weeks. It is also apparent that a majority of planetary systems have likely gone through a far more dramatic period of dynamical rearrangement or dynamical ‘cooling’ than ours has – leaving a tell-tale signature in the highly elliptical orbits of major planets.

This is just the tip of the iceberg. Although we don’t yet know much about the elemental and chemical composition of exoplanets, we do see a diversity in the contents and conditions of proto-planetary environments. We also suspect that the pathway to any individual world includes an enormous variety of essentially random events – the process of building a planet is highly stochastic.

On the face of it this might seem a little depressing. After all, finding an ‘Earth-like’ planet is often described as the holy grail of exoplanetary science, the location of another place that could harbor life in the cosmos. But if all worlds are unique it might be that there are no other places quite like Earth, and if a delicate set of conditions are critical for life this would put a damper on these prospects.

Meet the parents. Carbon chemistry abounds. (Credit:NASA/HST)

However, the chemistry of the universe does seem to be the very same chemistry from which we’ve sprung. Molecules made with carbon are ubiquitous, whether in the sparse interstellar medium or the thickening clouds of forming proto-stellar systems, organic chemistry dominates.

It also permeates the ancient material of our solar system that we see preserved in carbonaceous chondrite meteorites and cometary contents. And life on Earth not only got going fast some 3.5 to 4 billion years ago, it seems to have rapidly evolved into an interlinked world-wide chemical network that robustly preserves the vital genetic blueprints for metabolism and survival – the core planetary gene set.

While it is true that we do not yet know the actual answer, my personal take on all of this is the following. There may be no ‘Earth-like’ planet out there, but there are almost certainly Earth-equivalent worlds – alien but nonetheless amenable to life.

Only the most contrived and strained interpretation of what we see by way of the elemental and chemical composition of the cosmos and of terrestrial biochemistry would suggest there’s something ‘special’ about what happened here on Earth. Carbon-chemistry rules, and Earth 4 billion years ago was about as alien from Earth today as one can imagine, yet life started up fast. It’s going to happen in other places too.

So, we should not necessarily hold our breath for other Earth-like planets, but we should expect an astonishing diversity of equivalent places. I for one can’t wait to find out how the complex rough and tumble of molecular evolution played out on those other worlds.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity's Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Wileee 3:17 pm 12/26/2012

    What no one seems to mention is that our current methods for finding planets are unable to find planets in the earth size range. This is a huge block to finding true “earth type planets”.

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  2. 2. Caleb A. Scharf in reply to Caleb A. Scharf 4:07 pm 12/26/2012

    We can find earth size/mass planets (indeed there are detections now of sub-Earth sized objects) but it is true that this is close to the limits of either transit or radial velocity techniques – especially if the planets are orbiting Sun-mass stars or at Earth orbital radii. Some of the challenges involve the fact that stars are ‘noisy’ – they’re not the perfect backlight for these methods to work optimally and we’re hitting that wall. However, as we get more data we’ll be able to characterize stars better and better and push the detections to smaller and smaller worlds….

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  3. 3. genevehicle 4:42 pm 12/26/2012


    Kepler has found several planets in the “earth size range”. Of course, the large majority of extra solar planet discoveries have been massive planets with short orbital periods, but they’re just the low hanging fruit. Planets with smaller diameters and longer orbital periods (thus fewer transits in a given time period)just take longer to confirm. Take a look at the Kepler missions’ confirmed list. You’ll find quite a few planets with a diameter between .5 to 2 earth radii. Once again, most of those have short orbital periods and so there’s been enough time to gather the data needed to claim a discovery. However, there are more “earth-size” candidates with longer orbital periods that are amassing more data as we speak. Check out their site if you’re interested.

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  4. 4. Sciencefirstandforemost 9:20 pm 12/26/2012

    The Universe is 13.7 years old. 10 to the power 0f 21 stars. If one in a million stars has an Earth-like planet then that’s only a quadrillion Earth-like planets. The odds are that if there are this few Earth like planets then we would not have detected one yet.

    If one in a thousand stars has an Earth-like planet then that’s 15,000,000,000,000,000,000…more within our current technology but still ‘hard’ to detect/

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  5. 5. CBacon 10:52 pm 12/26/2012

    Indeed, what the above comment says is correct. Regardless of what the chances are, there are so many stars that at least a few of them are garunteed to have Earth like planets.

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  6. 6. dwbd 11:17 pm 12/26/2012

    I believe a statistical analysis, based on the probability of finding an Earth-like planet, with a similar orbital period, by current methods, vs finding the Gas Giants and short period Rocky Planets, using current catalog of discoveries, does demonstrate that likely Earth-like worlds should be very common.

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  7. 7. 3:35 am 12/27/2012

    I tend to subscribe to the “Rare Earth Theory”. You can look it up under that name in Wikipedia. The reason I subscribe to this pessimistic theory is the low probability of conditions that permit intelligent life to arise. I realize there are a lot of sites that might qualify, but it took us about 4 billion years to get to our current state of scientific knowledge and a lot depended on incredible luck. I would take the rough guess that there may be one technological sophisticated planet in every 1000th galaxy, which as there are in the order of 200 billion galaxies that would still make for th contemporary existence of 20 million scientifically advanced civilizations. Space travel is likely to be much more difficult than its current promoters believe. How did I pick one out of 1000 galaxies, frankly I just guestimated.

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  8. 8. Fanandala 3:56 am 12/27/2012

    Would our current instruments be able to detect earth if they were used on Proxima Centauri or Sirius?

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  9. 9. roj2003 5:08 am 12/27/2012

    Perhaps the hardest part is realising that even in the ‘habitable zone’ it took the Late Heavy Bombardment to deliver water to the otherwise waterless region where the ‘terrestrial’-type planets formed [less than 2 au from the stellar core]. This delivery seems to have arisen from the outward migration of the outer giant gas/ ice planets and THAT does seem less than usual (?).

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  10. 10. em_allways_right 9:37 am 12/27/2012

    IF there aren’t enough Earth-type planets we will just have to Terra form them.

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  11. 11. Jerzy v. 3.0. 10:25 am 12/27/2012

    False assumption here is that Earth is the most suitable planet for life possible.

    As the blogger pointed, Earth is not even fully in habitable zone, as polar regions are frozen.

    Earth also has too much water and too little carbon dioxide – over half of Earth surface is deep ocean which is biological desert.

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  12. 12. vinodkumarsehgal 10:45 am 12/27/2012

    Last but one para of the article itself suggests the presence of some ‘earth like planets’ in universe with some 10^21 stars and may be equivalent or even more planets.

    “Only the most contrived and strained interpretation of what we see by way of the elemental and chemical composition of the cosmos and of terrestrial biochemistry would suggest there’s something ‘special’ about what happened here on Earth. Carbon-chemistry rules, and Earth 4 billion years ago was about as alien from Earth today as one can imagine, yet life started up fast. It’s going to happen in other places too.”

    4 billion years ago, earth of that period was not only not “earth like” as it is today, it was not even ‘earth equivalent’ in the strictest sense. Yet life in some rudimentary form commenced billion of years ago on earth which has reached the present stage as we witness as on day.

    Who knows, life might have already started in some planets some billion of years ago and now civilization in those planets might have reached equivalent or even in advanced stage than as on earth. Astronomers and astro-biologists have no other means other than detection of light from remote stars for identifying the planets in their vicinity. But detection of planets even ” earth equivalent” planets shed no light on the presence of life in those planets.

    On earth itself, which has remained our abode for million, if not billion, of years, we are not sure of the mechanism of origin of life. After all, organic chemistry of carbon molecules is not life. Fact is that Science is yet not completely aware of ” what life is”?

    When on earth itself, our knowledge about life, its origin and evolution are so rudimentary, how we can have some credible knowledge about life in remote planets about whose geo-physical conditions we know almost nothing. But keeping into view vastness of universe and the harshness of conditions on earth in past during which life might have had its origin and it survived and thrived, odds appears quite high that there should be life in some corners of universe. But odds of our knowing the corners where life might be having its presence do not appear to be quite high unless some feasible technology for inter stellar travel is develope

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  13. 13. Sciencefirstandforemost 11:59 am 12/27/2012

    vino: “After all, organic chemistry of carbon molecules is not life. Fact is that Science is yet not completely aware of ” what life is”?

    True. More to the point ‘life’ is an arbitrary concept. The properties of matter and energy are the same regardless if it is found in what we call ‘life’ or non-life. Any interpretation of matter and energy that we see with our senses is just a macro overlay to make some logic of it all. Quantum happenings in a carbon atom are the same regardless of any label.

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  14. 14. Torbjörn Larsson, OM 1:01 pm 12/27/2012

    Earth analogs (Earth equivalent) planets is an old improvement on “Earth-like”. I don’t think the discovery that planetary systems are individuals picked from a much larger distribution than we could imagine is a problem but an opportunity. We will find life in more places.

    Which gets us to habitability. Of course it is only early measures to home in on potentially inhabited planets. The original usage didn’t include GW atmosphere models in order to simplify search, now it is routinely done. And the Habitable Exoplanet Catalog has gone over to an Earth Similarity Index to get rid of the problem that only a waterworld at 20 degC would be 100 % surface habitable.

    Something similar is going to be done with the different biosphere pathways, I’m sure. Earth is a typical surface habitable mesoplanet, but it has ocean and crust ecologies too. When we get to psychroplanets like Mars they are likely only crustal habitable, and when we get to extreme psychroplanets like Europa they are likely only ocean habitable (as they will most often have a pressure ice bottom). So we should end up with at least 3 major habitability categories.

    “Our system is also relatively spread out, it is increasingly apparent that the universe likes to build compact orbital architectures of numerous planets with orbital periods of days to weeks. It is also apparent that a majority of planetary systems have likely gone through a far more dramatic period of dynamical rearrangement or dynamical ‘cooling’ than ours has – leaving a tell-tale signature in the highly elliptical orbits of major planets.”

    It is an inherent tension in this. The reason why our appears spread out, and we have certainly examples of more spread, is that it has had a turbulent past. But not enough turbulence to end up with hot jupiters.

    And I don’t think that anyone has presented the statistic that suddenly everyone goes for, observer bias or not. Why, the recent Tau Ceti, that gave us 2 potentially habitables, have its outer habitable at about twice the period we have. Yet it was called a compact system just because it had more mercuries.

    I think we should look at the potential habitable trend. About half the potential habitables, 4 out of 9, have been delivered by planets with at least 2 habitables. (Someone mentioned that Gliese 581 may have more than 2 in some research.) The solar system is not “rare”, the Earth isn’t “rare” as it is a marginal runt for plate tectonics, instead it is marginal for life.

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  15. 15. Torbjörn Larsson, OM 1:43 pm 12/27/2012

    @ Willee: Kepler has listed Mars sized planet candidates, the Habitable Exoplanet Catalog has one Earth sized pending Kepler candidate and lists potential exo-moons. [ ]

    The current problem re Kepler (say) is that it takes 2-3 years to find an Earth analog with any method. (Earth massed planet around Sun massed star, so ~ 1 year orbit.) Due to noise problems, Sun is unexpectedly a tad on the calm side, Kepler needs the extended 7-8 year mission to reliably filter out such.

    @ Sciencefirstandforemost: Life arose on Earth so fast that abiogenesis can be tested (at 3 sigma) to be an easy process. (Fast and/or highly recurrent attempts.)

    In fact this year several thermodynamic results show that RNA replicators _will_ arise with a few 10s of thousands of years in hydrothermal vent conditions, because there is a thermodynamic force that ensures the process can’t stall. [For the force, see "Thermodynamic Basis for the Emergence of Genomes", Woo et al, PLOS Comp Biol 2012; for why only RNA can make the earliest replicators, see England's work which is still in review I believe - basically there is an entropic hurdle and nucleotides like DNA or peptides are too stable for non-genetic metabolism - RNA is "just right".]

    The upshot is that ~ 100 % of planets 7 billion years old with plate tectonics will get life. Those are far more frequent than 1 in a million. We have ~ 130 stars (including dwarfs) within 20 ly, so perhaps ~ 1000 within 40 ly. We can soon see oxygenated atmospheres out to that distance, I’m sure.

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  16. 16. Torbjörn Larsson, OM 1:48 pm 12/27/2012

    @fred: The bayesian “rare earth” idea is daft. (Not coincidentally, it is claimed to have arose by, and _have_ been pushed, by religious interests.)

    First, because it evidently doesn’t work for early life, it was too easy so Earth isn’t “lucky rare”.

    Second, because it is untestable, just pile on inconsequential conditions that lower the likelihood you want to lower. Even more untestable if you go for the too loosely constrained “Fermi’s paradox” setting.

    Third, because every biologist I know will tell you language capable intelligence is a rare trait comparable to the trunk of Elephantids. I.e. it arises once in a blue moon. You don’t need more than biology to know that.

    @ roj: Yes, the water drenched asteroids at ~ 10 % water by mass (the most common carbonaceous chiondrites) _is_ a problem for terrestrials that need to be ~ 0.05 % dry as Earth to host life as we know it. A factor 10 less water and little ocean, a factor 10 more water and little land.

    Luckily there seems to be a generic process that keeps the ice line beyond habitable terrestrials. (Disk turbulence.) And it keeps the carbon line well away too, or we would risk an outer carbon-to-diamond crust that keeps necessary metals from siliceous minerals away from the biosphere. (It can grow to occupy the outer 30 % crustal thickness on outer terrestrials, apparently.)

    And in our case the asteroid delivery of water and carbon has been too small to threaten surface habitability. IIRC less than half of the water can have been delivered after planet accretion, as measured by D/H isotope ratios. So we lucked out, but by a comfortable enough margin to hope asteroid water & carbon will not be a threat in other systems.

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  17. 17. Torbjörn Larsson, OM 1:58 pm 12/27/2012

    @ vinodkumarsehgal: Essentially your comment is an argument from ignorance. Besides being a fallacy, what potential use could it be for science? We are finding these things out as we write.

    “But detection of planets even ” earth equivalent” planets shed no light on the presence of life in those planets.”

    Many life indicators are researched as early possible observations, from oxygen of mature biospheres over cloud formation due to bacteria to light front effects from continental wide forests. This is not a killer problem, early tests using Earth light reflected on the Moon shows it is doable.

    Constraining the environments that leads to life couples back to abiogenesis theories, so we will shed light on all stages of life by these studies.

    “Fact is that Science is yet not completely aware of ” what life is”?”

    Evolution is the process that takes living populations to living populations, the process of life. The knowledge of the process and its generic mechanisms is sufficient to recognize it as opposed to, say, crystals.

    But since we can’t get up close, we will look at chemical imbalances originating from cellular metabolism instead.

    It is doable, especially as we now know all life must be RNA based. (Or at least, we know of no alternative heteromers that pass the thermodynamic bound for early replicators.) This pretty much constrain life to be CHNOPS (carbon, hydrogen, et cetera) based, and I think we can start to cut out psychroplanets like Titan out of the potentials. Early metabolism will almost certainly be CO2/H2O based, generating CH4 to build up cells.

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  18. 18. dwbd 2:00 pm 12/27/2012

    “…We can soon see oxygenated atmospheres out to that distance…”

    An important goal. And if we don’t we are gonna have to do some serious thinking about Fermi’s Paradox. We seem stuck with either we live in a simulated universe, that only allows life to develop on a small number of planets, maybe just one. Or we will be stuck once again to invoke the Anthropic Principle and take the position if intelligent life had arose with any significant frequency, our world would long ago have been inhabited by alien life and we wouldn’t exist. So just add that to the list of exceedingly improbable variables that are essential to the development of our universe and us. Of course, if infinite universes exist, as is a common speculation, then the highly improbable must happen occasionally.

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  19. 19. David Marjanović 2:10 pm 12/27/2012

    Earth also has too much water and too little carbon dioxide – over half of Earth surface is deep ocean which is biological desert.

    The carbon dioxide was there; it’s been removed by photosynthesis, by life itself.

    Desert… well… seawater is full of bacteria and archaea (the latter dominate in numbers below 1000 m).

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  20. 20. David Marjanović 2:27 pm 12/27/2012

    Hej, Torbjörn! You still carry your OM – why have you been absent from Pharyngula for so long?

    First, because it evidently doesn’t work for early life, it was too easy so Earth isn’t “lucky rare”.

    Misunderstanding. The Rare Earth Hypothesis doesn’t say that life is rare, it actually says life is common; it says complex, animal-like, life is rare.

    it is untestable

    Even today, paleontology can test some of its assumptions.

    Third, because every biologist I know will tell you language capable intelligence is a rare trait comparable to the trunk of Elephantids. I.e. it arises once in a blue moon. You don’t need more than biology to know that.

    Uh, that’s part of the point. Do you simply object to giving it a name? ~:-|

    we now know all life must be RNA based

    Could you provide a complete citation or a link to that PLoS Comp Biol paper?

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  21. 21. ssakamoto 6:26 pm 12/27/2012

    Great essay, thank you, Dr. Scharf for helping me understand what it being discussed when I read about “Earth like planet.”

    My understanding is that there are two reasons for seeking an Earth-like planet.

    1. To find other life. In this search, I can understand why Earth-equivalent planets, which are still vastly different from our home planet could be viable candidates for life.

    2. To spread our species off of our fragile world. In this case, I’m wondering what you think. Are Earth-equivalent planets also able to support human life? To use your rental car metaphor, sure, a sports car is more fun than a sedan, but they’ll both get me where I’m going. Does the metaphor extend to Earth-equivalent planets, or are you only talking about the possibility of finding a planet that could support life, but not our lives?

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  22. 22. SteveCarleton 10:34 pm 12/27/2012

    As far as I know, life has not spontaneously started independently of existing life on this planet. In other words, something quite unusual happened 3.5 billion years ago on this planet. Since conditions for life have been mostly favorable since that time with no new life lineages, it seems that the probabilities of finding life elsewhere is very remote.

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  23. 23. bobigeiger 11:15 pm 12/27/2012

    You guys run around in the universe like headless chickens. There is no other life out there, the earth is the only place where God created life. Disappointed? Angry? Guess who got here the problem? Use the brain God gave you.Bee fine, Hans

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  24. 24. dalbert 12:13 am 12/28/2012

    Nice article clarifying the criteria for “habitable worlds”. However, the idea behind this search puzzles me. If we did find a world that we could travel to which was physically, thermally and chemically like ours, and by the miracle of chance had developed it’s own life, it would still not be like earth biologically. We are so interconnected in real time to the small scale life which we evolved with — we are swimming in it, and it makes up the majority of our bodies. Wouldn’t any other living world we discovered come with it’s own alien biota, which would not be compatible with ours? I don’t imagine we could survive on another world unless we found one physically, chemically and thermally like ours, which did not have any life on it at all, and somehow infected it with our flora and fauna until it produced it’s own atmosphere. The idea that we could successfully do that seems many times more unlikely than the idea that we could find and travel to such a place.

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  25. 25. Grumpymartian 6:37 am 12/28/2012

    I was hoping that the eventual James Webb telescope may well reveal the content of extra solar planets.Would it then be possible to send an unmaaned mission with new technolgy propulsion systems?Or is a too simplistic hope?

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  26. 26. savvov 10:43 am 12/28/2012

    Article does not take into account, that the planet the Earth appeared casually in Solar system (~ 800 thousand years ago), a geographical kind of a planet and a condition of dwelling on this planet very much and very much differed. More details on the site the Dynamic model of the globe has proved changes on a planet during following II, III, IV stages. To you a concrete material about the past of a planet in Solar system, but the past of a planet in time I a stage differs – hence it is necessary to represent precisely what to search on other planets in other Galaxies. A material for clause write, if to you will allow to publish

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  27. 27. jwmeritt 4:06 pm 12/28/2012

    Guess it depends on how narrowly “Earth-like” is defined. However, there are places on Earth that would not qualify as Earth-like….

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  28. 28. And Then What? 7:12 pm 12/28/2012

    Should We Expect Other Earth-Like Planets At All?
    To hopefully lessen the risk of my being accused of possessing an excessive amount of Hubris and obvious arrogance I will keep my response to the above question short and succinct.

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  29. 29. @lloydcata 1:49 am 12/29/2012

    Even the recent discovery of water on Venus should supply us with a wealth of intersteller knowledge(…more than Mars?) because of the “climate differentials” that produce the enzymes of organic life.

    That is not to say that I am convinced of the ‘universal’theories presented at this time as to ‘meaning and matter’ of the term Life. There can be no expectation that ‘anything’ alien will have any resemblence to what we are expecting; or as it goes, “expect the unexpected!”

    “Knowledge is the Art of Discovery; there are no limits or boundaries.” -Aristotle

    Many say that Aristotle was a Philosopher; being teacher to both Plato and Pythagoraus, but I beg to differ. My master was an Artist. He was the only living man who did not ‘eat’ from The “Tree Of Knowledge”, …he painted the Picture!

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  30. 30. vinodkumarsehgal 10:25 am 12/30/2012

    Bobigeiger (22)

    Yes, I agree that it was thru some divine intervention ( God) that He created or was instrumental in creation of life on earth as a part of His Grand Intelligence Design. But in an observable universe extending to billion of light years having trillion of stars and equivalent or even more planets, why God will create life at earth only. Though I agree that it is beyond the capacity of human mind to read the intelligence of God, but a natural query arises : was the Grand Intelligence Design of God so imperfect that out of trillion and trillion of planets and stars, life appeared at one planet on earth only and all the universe remained barren devoid of life? A logical, rational and impartial mind will agree that God’s design can’t be so imperfect that life manifested at earth only. To insist on the assertion that life appeared at earth only is as much irrational as the assertion of materialists that life was created from matter only as a part of accident.

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  31. 31. Jerzy v. 3.0. 6:38 pm 12/30/2012

    Anybody counted exactly how big improvement of current techniques is required to detect Earth-like planets and confirm eventual water and oxygen?

    And how much would it cost?

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  32. 32. vinodkumarsehgal 7:48 am 01/1/2013

    Scope of detection of “earth equivalent” planets is limited up to size, mass, period and distance of planets from parent star. It does not shed much light on the presence of water, oxygen , atmospheric pressure and temp. in right proportion which are necessary for the presence of life as we observe on earth. Though water, oxygen and light may be necessary for the manifestation of life of the type we know as on earth but reverse of this may not be necessarily true. It will infer that that it is not necessary that life may be present in environments having water, oxygen and and light in proportion as found on earth. This being due to reasons since Science lacks complete understanding of life and its origin and evolution from organic compound of carbon. Organic chemistry of carbon may form the base at which life may reveal. But there is no necessity that life may compulsorily manifest in organic molecules. Had it been, all the regions of space having organic compounds of methane should reveal life. In view of this, there can’t be an automatic inference that Titan or any other planet or its moon in our Solar system having lakes of methane should also have life

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  33. 33. Caleb A. Scharf in reply to Caleb A. Scharf 11:11 am 01/3/2013

    Jerzey c. 3.0. – measurement of the atmospheric composition of Earth-sized planets is looming. JWST (the Hubble replacement due for launch 2017) has a shot at doing this for a few nearby star systems with planets transiting low-mass stellar parents (M-dwarfs). The next-gen of ground based 30-meter diameter and up telescopes will also have a shot at this. So it’s expensive ($1B to $10B) but within reach – and the total cost is comparable to a few days worth of military spending by the US alone.

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  34. 34. CharlieinNeedham 5:01 pm 01/3/2013

    One thing I have never seen estimated is:
    How many other solar systems have planets derived from an exploded supernova?

    Earth is such a remnant – hence its composition of so many relatively heavy elements.
    Our iron core; abundant carbon, oxygen and nitrogen; all the silica, calcium, etc. – all were formed at the center of a very large star – a supernova that exploded.

    How many of the planets out there in other solar systems are remnants of an exploded supernova?

    What are the odds of any one planet ending up with enough carbon, nitrogen and oxygen to start life and allow evolution of advanced species?

    What are the odds of a planet having an iron core allowing it to form a magnetic field to shield the planet from hazardous radiation?

    Just what are the odds that enough of the “right stuff” from an exploded supernova would all congeal in the “right place” to produce an earth-like planet?

    Just because there are other planets in other solar systems does not mean they can allow advanced life to evolve, even if simple organisms were able to emerge.

    Ode to earth’s supernova mother:

    Twinkle, twinkle great big star…
    However ever will you blow
    All your remnants in a great big show
    To put just the right ingredients in just one place…
    For an earth to form,
    And evolve a human race?

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