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Researchers Create 'Habitability Index' For Exoplanets

Posted by Soulskill on from the just-look-for-the-starbucks dept.

hypnosec writes: The Kepler Space Telescope has allowed astronomers to detect and catalog thousands of exoplanets and exoplanet candidates. With more powerful telescopes like the James Webb Space Telescope scheduled for launch, scientists will be able to check if any of these exoplanets are habitable. But these space telescopes are expensive to create, and access time is coveted. This means simply pointing telescopes to random exoplanets isn't a practical proposition. That's why researchers have created what they call a "habitability index for transiting planets," with which astronomers will be able to prioritize the use of space telescopes for finding habitable planets. Their paper is available at the arXiv.

52 comments

  1. We already had one by russotto · · Score: 4, Funny

    The most habitable worlds, of course, are class M.

    1. Re:We already had one by Anonymous Coward · · Score: 1

      You do realize that those classes are fictional, don't you? And according to those classifications, other classes besides M are habitable though perhaps not by humans. Looking through the solar system, here's how I'd classify the planets:

      Mercury: Class K (because of the lack of atmosphere, but sufficient gravity)
      Venus: Class N (generally these are planets with high CO2 and sulfides in a very thick atmosphere, though class N has been used for other purposes, too)
      Earth: Class M
      Mars: Class K (again because of the lack of atmosphere, but enough gravity)
      Jupiter: Class J (large gas giant, probably not a super gas giant, which would be class T, though it could also be class S)
      Saturn: Class J (same as Jupiter)
      Uranus: Class I (smaller than Jupiter and Saturn)
      Neptune: Class I (smaller than Jupiter and Saturn)
      Pluto: Class D (mostly because it's a planetoid, though it could be class Q because of its eccentric orbit and the impacts; possibly class K if gravity is sufficient but with an extremely thin atmosphere)

      It's actually a pretty awful way to classify planets, because there are arguments why a planet might belong in several classes and it doesn't consider the huge range of possibilities for planets.

    2. Re:We already had one by dgatwood · · Score: 2

      The most habitable worlds, of course, are class M.

      Well, you should at least find plenty of Roddenberries.

      --

      Check out my sci-fi/humor trilogy at PatriotsBooks.

    3. Re:We already had one by ememisya · · Score: 1

      Well, long time ago the earth was flat, and nothing lied beyond the oceans. Maybe it's time.

    4. Re:We already had one by Grishnakh · · Score: 4, Informative

      Yes, they're fictional, but it's a good start, since after all it proves that modern-day researchers weren't the first people to think of classifying planets by their habitability characteristics. Also, the simple "class [letter]" scheme is easy to remember and use; I sure hope they don't come up with some arcane, complicated system instead. Finally, they should definitely use "Class M" to refer to Earth-like planets simply to pay homage to Star Trek. Everyone and his brother knows what a "Class M" planet is, as long as they watched some Star Trek within the last 50 years.

      It looks like you got your classes from Star Trek too, as seen here, but with some differences. I'm not sure where you got Class Q or I. The system probably does need a little revision though. Class H's "generally uninhabitable" doesn't tell you why. The Class P (see appendices) for icy planets is a good example. Class N for "sulphuric" really isn't sufficient; Venus is more like the Class Y "demon planet" except there's no dilithium-based biomimetic lifeforms, but the fact that Venus is so hot is important it needs to be classified that way. If a planet is too cold or too hot to live on, that's an important factor for humans. Same if there's no atmosphere. A planet (or moon) that's not too warm or hot but has no atmosphere can still be inhabited using domes or other sealed habitats, so that should be a class by itself. Mercury probably wouldn't fit there however, because it's much too hot. But it's hot in a different way than Venus, so they should have different classifications (hot because it's too close to the star, vs. hot because it has a thick atmosphere and runaway greenhouse effect). Finally, moons and planets should be classified together. The orbital path doesn't really matter (except insofar as it affects the climate/temperature). There could very well be Earth-like moons out there somewhere, so those should be Class M (like the moon in "Avatar").

      So here's my proposal which borrows from ST:
      Class M - Earth-like, small, rocky, oxygenated atmosphere, right temperature
      Class D - small, rocky, little to no atmosphere, right temperature, inhabitable with sealed habitats (e.g. Mars)
      Class J - gas giant (any size; this may be expanded later after we explore more star systems and decide we need to classify them further)
      Class E - small, rocky, little to no atmosphere, too cold (e.g. Pluto)
      Class F - small, rocky, little to no atmosphere, too hot (e.g. Mercury)
      Class G - small, thick atmosphere, too hot (e.g. Venus)
      Class A - very very small, not spherical (e.g. moons of Mars, captured asteroids)
      Class B - very small, spherical but extremely low gravity (e.g. Sedna, Ceres, Pluto, dwarf planets in general)

      I'm probably missing something here, perhaps planets with only liquid surfaces. I avoided calling Venus "Class N" because it sounds too much like "Class M".

    5. Re:We already had one by Anonymous Coward · · Score: 0

      The most habitable worlds, of course, are class M.

      Yes, but you're looking for an actual planet. Earth is no longer considered a planet, in fact by most it was never considered a planet. No one wants to bring this up because humans think they're so special and the shitty meteoroid they live on is "the bestest ever!!". Pathetic, you earthlings are the most feeble minded, greasy bunch of idiots the universe has ever seen.
      Nice planet bro, lol.

    6. Re:We already had one by Anonymous Coward · · Score: 0

      Class H - large, rocky, heavy, gravity too large to support humans

    7. Re:We already had one by Anonymous Coward · · Score: 0

      Same AC as earlier replying, thanks for the good post. I'm not opposed to classifying planets with letters. It's a simple way to do it and those familiar with science fiction will recognize the scheme. My attempt at classifying the solar system was based on Star Trek's scheme as described in the "Class M planet" Wikipedia article. The biggest issues I have are that the letters don't take into account the full range of planets that might be reasonably encountered and it's very possible for a planet to fit in more than one class. I don't object to labeling earthlike planets as Class M. Planets that are more marginally habitable probably should be letters close to class M, and those that are unlikely to have life can be elsewhere in the alphabet. Things like L, N, and O probably should be marginal planets. I think there'd need to be some kind of decision tree and, for example, being a gas giant is probably a more important distinction than the lack of liquid water.

      As for what might prevent life or at least complex organisms from existing, or even rendering it uninhabitable to us but perhaps not to other complex life, here are some ideas:
      1) Gas giant
      2) No atmosphere or extremely thin
      3) Too hot or too cold (orbit is in an uninhabitable zone)
      4) Too thick of an atmosphere
      5) Lack of liquid water present
      6) Toxic or corrosive atmosphere
      7) Too large or small
      8) Surface covered in water or ice (but in a potentially habitable zone)
      9) Protoplanet, not yet cooled
      10) No molten core, lacks magnetic field (probably no atmosphere, but also exposure to harmful stellar radiation)
      11) Tidally locked to the star
      12) Very eccentric orbit causing large shifts in weather
      13) Orbits a stellar remnant like a white dwarf
      14) Rogue planet, doesn't orbit any star (ejected from a star system, perhaps)

      These don't all need their own categories because some might be able to be combined together. I'd propose something like this:
      A: Protoplanet
      B: Dwarf planet, very tiny
      C: Too small of a planet, rocky surface
      D: Little or no liquid water present, a desert planet
      E: Too large of a planet, rocky surface
      F: Rocky planet with a corrosive atmosphere
      G: Orbits too far from a star to be habitable, too cold
      H: Orbits too close to a star to be habitable, too hot
      I: Gas giant, larger than Jupiter
      J: Gas giant, Jupiter-sized or smaller
      K: Possibly habitable, but with a toxic (e.g., methane, ammonia) atmosphere
      L: Marginally earthlike, too hot
      M: Earthlike
      N: Marginally earthlike, too cold
      O: Marginally earthlike, atmosphere is too thin or composition barely supports life
      P: Would be habitable, but covered in ice
      Q: Would be habitable, but covered in water
      R: Very thin or no atmosphere
      S: Very thick atmosphere
      T: Tidally locked to the star
      U: Solid core, lacks magnetic field
      V: Rocky planet with an unusual composition such as lacking carbon
      W: Planet with an irregular orbit that causes changes in weather during its year that make it uninhabitable
      X: Not likely to support life, but unusual and doesn't fit well in other categories
      Y: Orbits a stellar remnant
      Z: Rogue planet, not in a solar system

      I'd give priority to classifications farther away from M, with the exception of things like I & J (gas giants) that I'd probably classify earlier than anything but Y & Z.

    8. Re:We already had one by Intrepid+imaginaut · · Score: 1

      If we're grading planets according to habitability, it's fairly binary - habitable or non habitable. Until we've mastered the effects of low or high gravity on people anything not almost exactly earthlike is going to be more effort for less return than a large space station. You might fine tune it a bit by adding a third category - habitable with modifications, like say a semi toxic atmosphere you can survive with air filters. Even then considering how much of the earth's atmosphere is a result of its biosphere the odds of finding an earth-compatible world without running into huge ethical problems regarding the disruption of its native life forms is minimal.

      So here's my ad hoc categorisation scheme which no doubt the scientists involved have already superseded.

      Class A: Completely human compatible, habitable and uninhabited.
      Class B: Completely human compatible, inhabited by something.
      Class C: Moderately human compatible, can be terraformed or colonists genetically engineered for unprotected compatability, uninhabited.
      Class D: Moderately human compatible, can be terraformed or colonists genetically engineered for compatability, inhabited.
      Class E: Inhabitable with sanctuary (sealed compartments, very difficult to develop, think Mars or the moon), uninhabited.
      Class F: Inhabitable with sanctuary, inhabited.
      Class G: Completely uninhabitable (like Jupiter).

    9. Re:We already had one by Hognoxious · · Score: 1

      Classifying and indexing aren't the same thing.

      --
      Confucius say, "Find worm in apple - bad. Find half a worm - worse."
    10. Re:We already had one by angel'o'sphere · · Score: 1

      If you invent such a schema then Class-E is obviously "earth like".

      There is absolutely nothing "easy to remember" in your schema.

      --
      Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
    11. Re:We already had one by Anonymous Coward · · Score: 0

      Haha, that's what I was going to add...

    12. Re:We already had one by Anonymous Coward · · Score: 0

      Could you provide a citation for this odd belief?

      https://en.wikipedia.org/wiki/...

      But in any case, now we know it's spherical, and how utterly vast and terrifyingly empty the universe is, maybe you can adjust your beliefs in the light of new evidence?

    13. Re:We already had one by Anonymous Coward · · Score: 2, Funny

      Class H's "generally uninhabitable" doesn't tell you why.

      It's typically because there is a giant blob of an amorphic entity bent on making doppelgangers of anyone who steps foot on them. Also the atmospheres are typically highly corrosive. The "H" in "Class H" is short for "Hell."

    14. Re:We already had one by Anonymous Coward · · Score: 0

      I've always liked the classification system used on Orion's Arm. Earth and similar planets have the simply classification of "Gaian" and then there are variations based on things like ocean coverage, surface temperature, and atmospheric O2 content.

    15. Re:We already had one by Grishnakh · · Score: 1

      It does seem like having multiple letters (or numbers) is starting to look very useful, because several of these characteristics can apply to the same planet; for instance, Venus would be class S and K, so maybe it should be "Class SK", while Mercury would be "Class CHT".

    16. Re:We already had one by Anonymous Coward · · Score: 0

      small, thick atmosphere, too cold (Titan)

    17. Re:We already had one by Anonymous Coward · · Score: 0

      Class M comes from Minshara class. It's Vulcan language term for Earth-like planets.
      If you go Star Trek then go the full length, scrub.

    18. Re:We already had one by Anonymous Coward · · Score: 0

      But in any case, now we know it's spherical

      Actually it's an oblate spheroid, not a sphere.

    19. Re:We already had one by s.petry · · Score: 1

      Yes, they're fictional, but it's a good start,

      Perfectly appropriate too, since habitation off of earth is also fictional.

      --

      -The wise argue that there are few absolutes, the fool argues that there are no probabilities.

    20. Re:We already had one by rubycodez · · Score: 1

      I note you link to a biased source rather than the peer reviewed truth of the timecube website

  2. Sounds like some good science there... by Anonymous Coward · · Score: 0

    We can tell how habitable it is by how much it causes a start to warble or how much light it blocks during transit. We have no change of ever getting there and exploring via probes or otherwise. Can't we just be happy that you found evidence of some other bodies out there with some pretty extreme methods?

    1. Re:Sounds like some good science there... by Rei · · Score: 1

      We can tell how habitable it is by how much it causes a start to warble

      Chirp chirp chirp, triiiiiiiiiiiillll, triiiiiiiiiiiiiiiilllll! Chirp triiiiiiiiiiiiiiiiiiillll! Coooo-oooo! Cooooo-oooo! Chirp chirp chirp!!!

      --
      The human body can be drained of blood in 8.6 seconds given adequate vacuuming systems.
  3. Next ... the 'climate change' index ... by Anonymous Coward · · Score: 1

    Don't ever forget 'climate change', you insensitive clod!

  4. How about the QA index? by Anonymous Coward · · Score: 0

    Which is the reachability index. Oh yeah, it's ZERO.

    1. Re:How about the QA index? by Anonymous Coward · · Score: 0

      You're boring. Please, leave.

    2. Re:How about the QA index? by Anonymous Coward · · Score: 0

      Nah, you know what's boring? A bunch of pre-teen fanbois repeating the same tired space age clichés that will never, ever happen, ever. But keep pretending it's not a religion.

    3. Re:How about the QA index? by Coren22 · · Score: 1

      repeating the same tired space age clichés that will never, ever happen, ever.

      I think it is you that is living in fantasyland. You are claiming that it will never happen, which the evidence contradicts.

      --
      APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
    4. Re:How about the QA index? by rubycodez · · Score: 1

      It is certainly within the ability of current human scientific and engineering ability to send an unmanned probe to the nearest three stars in less than two centuries with nuclear fission power alone

    5. Re:How about the QA index? by Anonymous Coward · · Score: 0

      Evidence contradicts? Space Nutter, ex global warmonger and most likely to be a Biden supporter as soon as Hillary tanks.

  5. Anything voted most livable exoplanet by Ukab+the+Great · · Score: 1

    Will likely be invaded by freeloading yuppies the following year.

    1. Re:Anything voted most livable exoplanet by Anonymous Coward · · Score: 0

      Twat.

    2. Re:Anything voted most livable exoplanet by Hognoxious · · Score: 1

      The bastards. At least with hipsters you know they'll be gone after a year or two, when it's gone mainstream.

      --
      Confucius say, "Find worm in apple - bad. Find half a worm - worse."
  6. Is this for real? by Anonymous Coward · · Score: 0

    Is this, like, for real? OMG I would like totally like to see another planet but I wouldn't want to, like, be stuck there, like forever!

    If I could be the first to be on Mars like before all my BFFs that would be totally awesome!

  7. My question is ... by Anonymous Coward · · Score: 0

    How would a habitability index distinguish between planets in our solar system like Mars, Earth and Venus which simply due to placement and individual mass, would probably score high habitability but as we all know have high in the case of Earth, median habitability in the case of Mars and probably a negative value for habitability for Venus.. just a problem they appear not to have considered.

    1. Re:My question is ... by Rei · · Score: 2

      I think it's silly in the regards that we have precisely one datapoint about the sort of environments in which life may exist, which is pretty terrible in terms of making any sort of definitive statement. I'd much rather they keep their options open, check out a wide range of environments, and just look for signs of "things that are hard to explain", whatever they may be. "Hmm, this body has both a strong oxidizer and a strong reducing agent in its atmosphere - how is that happening?"

      I'm not saying "check planets in random order" or anything of that nature. Just that I don't think it's critical to obsess over being sure to examine them in order of "earthishness" from highest to lowest. We need to be looking at a diversity of worlds.

      Heck, we don't even know whether the surface of a body is the best place to look, most life in the universe might be in sub-crustal layers for all we know. Certainly would partially help explain the Fermi paradox, if it were such that we rare "surface dwellers" have a far easier route to the cosmos than something that needs to be under gigapascals of pressure to survive and whose radiating transmissions, if any, would be blocked by their planet's crust.

      --
      The human body can be drained of blood in 8.6 seconds given adequate vacuuming systems.
    2. Re:My question is ... by Anonymous Coward · · Score: 0

      I agree it'd be worrisome if astronomers were focusing entirely on one possible scenario for life, and ignoring others. But they do seem to look at a range of options - for example, see this recent story, in which some astronomers looked for heat-signatures of galactic-scale civilisations.

      If I had to bet, though, I'd guess that the first detection of extraterrestrial life will be something like the scenario you described: an astronomer will be looking for something entirely different, see some funny results, and think "how is that happening?".

    3. Re:My question is ... by Anonymous Coward · · Score: 1

      Yes, there's only one data point of a planet supporting life. While we can't draw conclusions from that about which planets are habitable, it's very important for at least a couple of reasons:

      1) We have no evidence that any planets of any other types are capable of supporting life. We've only seen one planet known to support life, especially intelligent life. That is, of course, Earth. Why not start by looking at planets like the only one we are certain is capable of supporting intelligent life?
      2) If life evolves on other types of planets, it may well not at all be like our own. This is a good place to look first because we have some idea of what to look for by looking at how life has evolved on our own planet. We have a relatively good chance of being able to identify and understand life like that on our own planet.

      With respect to the diversity of life in the universe, we see it on Earth in the form of extremophiles. There is truly bizarre life that has adapted to survive in virtually every environment anywhere near the surface of the Earth. There is no reason to assume that this couldn't happen elsewhere. However, we may be able to place some limits on where we think it is most likely to develop.

      Your example is subterranean beings, an example that I'm not convinced is likely. In order for life to perform the functions that make it life, it consumes a lot of energy. Much energy is also lost to the environment through heat. This seems like a limitation of the universe that can't be circumvented. In order to sustain life, the energy that is lost must be replaced. There are many ways this can be accomplished. Photosynthetic organisms convert light into chemical energy. Organisms in the deep oceans tend to rely on geothermal energy. There are bacteria that use redox reactions to harness energy from chemicals in their environment. And there are predators that obtain energy by consuming other organisms. Regardless, it's essential that there be a continuous influx of energy in order to sustain life. In the case of subterranean beings, this seems most likely to be in the form of geothermal energy or, perhaps, the decay of radioactive isotopes if present in sufficient quantity. That said, it doesn't seem to be the most likely place.

      However, just because there's abundant energy to consume doesn't mean it's a favorable place for life. There's a tremendous amount of energy in the sun, but it doesn't seem to be the most likely place for complex organisms to develop because of its composition. Although Jupiter doesn't produce energy through fission like the sun does, there's also a vast amount of energy from the extreme winds and pressures in its atmosphere. Again, because of the composition, it seems unlikely that complex life would develop to use this energy.

      The problem with extremophiles becoming complex and intelligent is that only a small portion of life actually does this. Most life is very simple. It takes a lot of energy to for complexity and intelligence, and is only worth it if a survival advantage occurs as a result. One of the driving forces of evolution is random mutations and the resulting natural selection. If a greater diversity of life exists in a region, it seems more likely that those mutations might eventually evolve into an intelligent being. On the other hand, extremophiles must be highly adapted for their particular conditions, which don't really support diversity and may not provide sufficient energy to allow for complexity and intelligence. The less harsh conditions in relatively close to the surface of bodies of water and also on land seem much more likely to lead to intelligent life.

      So, although it's possible that life exists in very different forms, perhaps likely, there are reasons to believe that those aren't the most likely places for complex or intelligent life to evolve.

    4. Re:My question is ... by Rei · · Score: 2

      I have no clue where you're coming from. You rightly point out that life takes energy, but then proceed to consider internal sources of energy as worthless, when in reality in the universe far more things are exposed to internal energy than external. And radioactive decay-driven energy sources are only one. For example, Encelaldus's heat seems to be driven by the serpentization of rock, which also releases hydrogen, a potential food source to microorganisms. There are numerous chemical means which can release vast amounts of energy - yes, nuclear energy is many orders of magnitude more dense, but non-radioactive elements are also orders of magnitude more common.

      Anywhere that there is heat and fluids (or solids that can undergo solid-state convection) can experience that heat being turned into harvestable forms of chemical energy, because chemical equilibriums are different at different temperatures. For example, at STP conditions, N2 + O2 is favorable, while at high temperatures NO2 is more favorable. N2 + O2 that goes to higher temperatures and forms NO2, which then comes back down to the lower atmosphere, is bringing a source of chemical energy with it.

      Since heat differentials can and will be readily converted to chemical energy wherever it's associated with convection of any variety, then any source of heat is a fuel for life - and heat most definitely doesn't only come from nuclear decay - or chemical reactions. It comes also from the rebalancing of layers to a lower gravitational equipotential. It comes from impacts. It comes from tidal heating. It comes from thermal cycling in elongated orbits. It comes from mass loss due to solar wind exposure. There's a vast range of potential heating sources in the universe that can create heat differentials. And heat differentials make exploitable chemical reactions.

      You make blind assertions that "these environments wouldn't be likely because of their composition". What do you know about this? You have a sample size of one of chemical processes that have created life. We can't even see deep into our own world to see what other alternatives might exist at higher pressures, let alone in other worlds. Heck, underground doesn't even mean particularly high pressures. Dwarf planets can have Earth-surface pressures at hundreds of meters or even kilometers depth. And life on Earth exists fine in the deep sea, wherever there's energy to support it, where pressures are at over 1000 atmospheres

      Deep environments might prove even more prone to organic chemistry. In general, pressure is usually associated with faster reaction rates. You also often have more complex arrangements of possible chemical phases for each compound at higher pressures than with lower pressures. Water for example over its possible temperature range at a particular depth might have 3-5 potential ice phases, a liquid phase, a supercritical fluid phase, and a gas phase. This leads to a much greater range of possibilities for reactions to potentially exploit, because each chemical in each of its phases has the potential it interact with each other chemical in each of its other phases, or in the case of non-metastable forms, at least many of its other phases.

      Common theories for the origin of life on Earth usually assume that it wasn't the sun that powered the first forms of life, even though that's the most convenient source of energy on our planet. Photosynthesis is much more complicated than most forms of chemosynthesis. Environments like black smokers, volcanic pools or acidic waters within deep iron-rich minerals seem like far more likely candidates.

      Intelligence evolving within creatures that live in liquids? Oh, we've never seen that before! ;) Except, of course, for the fact that the second-most intelligent category of mammals are aquatic (cetaceans), and the most intelligent invertebrates (mollusks) live there too. Rather, the oceans tend to be highly competitive environments, and thus good breeding grounds for intelligence.

      --
      The human body can be drained of blood in 8.6 seconds given adequate vacuuming systems.
    5. Re:My question is ... by Rei · · Score: 1

      ** I should clarify that when I say "mollusks", I mean like cephlapods, not like snails ;)

      --
      The human body can be drained of blood in 8.6 seconds given adequate vacuuming systems.
    6. Re:My question is ... by Anonymous Coward · · Score: 0

      Anywhere you have sufficient energy available and replenished at a fast enough rate and the necessary elements and chemicals for life to form, you can sustain life. And yes, life probably did develop initially around things like volcanic vents on the sea floor before moving to other areas. The energy comes from heat and redox reactions involving metals. This is common across many environments on Earth, not just on the seafloor. Chemosynthesis and photosynthesis don't actually have to be the only sources of energy, either. There's no reason that things like motion can't also be used as sources of energy for life. We have technology that extracts energy from motion, so I see no reason life couldn't evolve to do this either.

      With respect to the chemical composition, the sun and Jupiter are very rich in hydrogen, but tend to lack heavier elements outside of their cores. Hydrogen has great importance to life, but all the reactions you described require more than that. I don't think you can have life entirely based on hydrogen. :) That said, there may well be environments where things like ammonia, silicon, germanium, aluminum, and iron are among the building blocks of life. The environments with high pressure and temperature might better suit life that isn't carbon-based, some of the very things you were talking about. For that matter, I'll pose the question of whether a von Neumann probe would constitute life, and not merely evidence of the life that constructed such a device?

      You're right that I didn't clearly state my objection. I think my real issue is the idea that subterranean life is a solution to the Fermi paradox. That doesn't make sense to me. In order for life to contact us, it need be sufficiently intelligent to create the tools necessary to do so. Life on Earth has colonized just about everywhere that's remotely supportive of it, whether it's the surface, the seas, deep oceans, soil, and anywhere with enough energy and the chemicals to sustain it. Even if subterranean beings existed on other planets, if conditions supportive of life were met on the surface, I'd propose that life would be likely to colonize that surface. Furthermore, as intelligent beings, we've gone to places that ordinarily couldn't come close to supporting Earth-based life, although temporary. If intelligent subterranean life is abundant in the universe, I find it remarkable that some of it wouldn't find a way to visit the surface or send up a probe and have a look around.

      As for the prioritization of where to look for life, we know of one planet that presently supports life. We don't know where else in the universe life might exist or what form it might take. It may be that life very different from our own, perhaps with a different biochemistry or even something totally different (like my von Neumann probe example) is more common. Because the universe is vast and we only know for sure of one planet that supports life, we choose to look for similar planets first and then move onto other things. That makes sense to me.

    7. Re:My question is ... by Rei · · Score: 1

      But my analogy is this. Say that you're a pearl diver. You're browsing along a dive forum one day and see a picture from someone on their vacation to a remote tropical island holding a large, rare pearl that they found on a dive. You ask them where they found it, and they tell you they only did one dive and found it in waters of about 15 meter depth off the shore. Wanting to find many of these such pearls, you head out to the island. Now, you have two approaches you could take.

      1. Spend a long time carefully doing a geological survey of the water depth around all of the shores of the island. Then do your dives in order of which are most precisely 15 meters deep, regardless of how convenient they are to access. Only move on to areas that are any more or any less than exactly 15 meters deep when you've exhausted all of the known 15-meter depth areas.

      2. Go out and start diving wherever the water looks to be at least in the right ballpark of 15 meters depth. Start with the most convenient areas first. Don't obsess over the exact depth - exploring some 10 meter areas, some 20 meter areas, etc, just trying to keep it roughly in the ballpark of 15 meters. Because hey, for all you know, more than 15 meters or less than 15 meters might be an even better diving depth; you've only got one datapoint so far.

      Which makes more sense? #2, obviously. Which is the same strategy we should be using with exoplanets in the search for life. We should be "favoring" Earthlike planets, but not obsessing over earthlike-ness in the search. We should be checking out a diverse range that is only "centered" on Earthlike bodies. And we should be focusing on those which lend themselves to easier, more detailed observation first, such as those closer to us and with a more favorable orbital alignment.

      --
      The human body can be drained of blood in 8.6 seconds given adequate vacuuming systems.
    8. Re:My question is ... by Anonymous Coward · · Score: 0

      With current technology it probably won't.

      Once they can get a spectra analysis of the exoplanets then can bucket them based on the chemistry of their atmosphere. Which is actually the only thing they need to spot a habitable environment as the only known way to get an Oxygen heavy atmosphere like Earth's is to have organisms manufacture it.

      But that's still too hard so instead estimating the pressure and temperature conditions that would support the chemistry needed for the life needed to make an atmosphere needed for human habitation, then using orbital data to determine if the mass and distance from parent is right for the pressure/temperature range, is the best we can do

  8. Don't Forget Class Z by Anonymous Coward · · Score: 0

    It's Earth-like, but populated by zombies.

    1. Re:Don't Forget Class Z by rubycodez · · Score: 1

      That's fine, it implies suitable for humans or similar advanced life as necessary zombie-fodder. It implies a level of non-human sentience too for zombies to vocally express the longing for braaaaaaaiiiiiinnnssssss. Finding a class Z is a win-win

  9. Dang. by jtownatpunk.net · · Score: 1

    I thought that said "hitability".

  10. Utah by Anonymous Coward · · Score: 0

    Wait, okay, so where does Utah score for habitability compared to everywhere else?

    1. Re:Utah by rubycodez · · Score: 1

      There is thriving (non-sentient) life there already, they're called mormons

  11. Trying to resist... by jmcwork · · Score: 1

    Has anyone classified ... (must stop) Ura....NO! (throwing keyboard across room)

  12. Niven's Scheme by Anonymous Coward · · Score: 0

    Author Larry Niven's "Known Space" series had an essentially binary scheme, stemming from a short-sighted programming feature of the original probes sent out to find habitable planets. The scheme was essentially "yes, habitable" or "no, not habitable". The oversight was that if the probe found anywhere on the target planet habitable, it returned "yes".

    Thus the establishment (by colony slowboats) of colonies on places like Mt. Lookitthat on Plateau (a California-sized plateau with habitable climate on a planet otherwise like Venus), or Jinx, habitable only in a narrow band toward the East Pole (it's a massive moon of a superJovian, tidally locked and with high gravity). Or We Made It, whose 90-ish degree axial tilt leads to periodic ground-level jetstream winds which weren't blowing when the probe made its flyby.

    For that matter, only a fraction of Earth's surface is habitable without substantial tech. You have to exclude the oceans, ice caps, and deserts.

  13. Traveller system by Anonymous Coward · · Score: 0

    The RPG Traveller has a pretty good sysem for classifying planets, based on three variables: size, atmosphere, and hydrosphere. It doesn't exactly handle temperature except that would be reflected by the atmosphere/hydrosphere stats. http://wiki.travellerrpg.com/Universal_World_Profile

    There's other stuff more relevant to the game, of course, but the above three are pretty generic.