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Finding Twin Earths Is Harder Than We Thought

Posted by timothy on from the earth-times-two dept.

Matt_dk writes "Does a twin Earth exist somewhere in our galaxy? Astronomers are getting closer and closer to finding an Earth-sized planet in an Earth-like orbit. NASA's Kepler spacecraft just launched to find such worlds. Once the search succeeds, the next questions driving research will be: Is that planet habitable? Does it have an Earth-like atmosphere? Answering those questions will not be easy. 'We'll have to be really lucky to decipher an Earth-like planet's atmosphere during a transit event so that we can tell it is Earth-like,' said Kaltenegger. 'We will need to add up many transits to do so — hundreds of them, even for stars as close as 20 light-years away.'" The abstract of their paper offers a link to the complete paper as a 17-page PDF; here is a short description from 2007 of the same researchers' work, outlining the type of spectral signature that an Earth-like atmosphere would be expected to show.

17 of 161 comments (clear)

  1. In effect, what they are saying, is by Jane+Q.+Public · · Score: 5, Interesting

    that it will take hundreds of years to tell if they are truly Earth-like. And that is complete nonsense.

    Once we find a sufficient collection of candidate planets using this instrument, we can devise a different device/experiment to narrow down whether they are Earth-like. That should take maybe a few years to ten years.

    That is more-or-less the pattern we have been following, and it has been successful so far. I see no reason to change.

    1. Re:In effect, what they are saying, is by TapeCutter · · Score: 2, Interesting

      I was 10 when I watched Armstrong land on the moon, every kid was into space and I had read "grown up books" in the library with pictures of water canals on Mars and rainforests on Venus. Since then astronomy has been fully digitised and we have mapped most of the EM spectrum. I'm not saying it won't continue to improve (especially in the area of corrective optics) but I think it will be slower now that the spectrum land rush is coming to an end and digitization is well and trully complete.

      The long term limiting factor with all astronomical technology is signal to noise, there have been huge advances in my lifetime concerned with the accuracy of finding and ploting the signal, but you still have to collect the photons. Mirror making tech is old tech but even it took a big jump in the seventies, I remeber reading how they made the mirror for Hubble sometime in the late 70's. It's the gold standard for mirrors (~1mm deviation over an area the size of Australia), I know, pity it was the wrong shape.

      Thing is, the electronics are now that good that we no longer need large mirrors with that degree of accuracy, we can larger less accurate mirrors and then correct for known distortions, even real-time chaotic ones such as atompospheric wobbles.

      I don't think Kepler will be a situation where someone announces "the answer", the best "iconic image" we will have to print on our T shirts will be a spectrum. How long it takes to get to the T shirt stage depends on how many candidate planets, their orbits, the number of photons we can catch and plot, and most of all, how confident do you want to be about yes/no.

      --
      And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
    2. Re:In effect, what they are saying, is by Nyeerrmm · · Score: 3, Interesting

      From what I can tell in a brief skim, it really does pose a fundamental limit given current technology. The problem is that with the largest mirror we can imagine getting up into space, and with the highest sensitivity sensors, the signal-to-noise ratio is still too low to get a usable measurement without taking hundreds of measurements.

      They plan to detect the chemicals in the atmosphere by measuring the absorption bands in the starlight as some of it passes through the atmosphere. This is presumably going to be a lot more sensitive than trying to detect the light from the planet directly, since you have a lot more photons to carry the information. The signal to noise ratio in this case is really limited by the unfortunate fact that light energy is discretized and you can't make finer measurements than a single photon. Thus a large mirror with a high-quantum efficiency (95%) sensor, is really the best you can do.

      The only hope to improve this is to either get bigger mirrors, which really depends on improving space access and is unlikely to give order of magnitude improvements, or to implement an as yet unrealized method that is able to get more information. If it were a problem of angular resolution there are plenty of interesting tricks you could use to improve it. Unfortunately I can't think of anything better, and it doesn't seem anyone else has yet either. Of course, that doesn't mean no one will... but its not as simple as just designing the next mission.

      Actually... random 3:30 am idea... if you did something in thermal-IR, and measured the absorption of the blackbody emissions of the planet by the atmosphere you might be able to get something working. The intensity would be a lot lower than looking at the stars light, but the dimming due to absorption would be much larger percentage-wise... although it would take some heavy math to show if it would actually give you a better SNR. Of course, there are plenty of holes here: among other things, my knowledge of atmospheric chemistry and absorption is very limited, and this would all depend on being able to resolve the star separate from the planet, and would thus rely on some complicated interferometric methods....... and you'd have to block out the star light to be able to get the planet light as anything more than noise... and probably the number of photons in thermal IR from a planet are too low to be able to even see it on its own... but maybe I'm wrong and it could work, or something else can.

    3. Re:In effect, what they are saying, is by Z00L00K · · Score: 2, Interesting

      Just because it's hard doesn't mean that we shall give up trying.

      This field is still a very young field, and the methods used to find planets will be more and more refined over time.

      But it's also important to not count out stellar systems that may not look like they are going to contain earth-like planets. Even a negative answer is an answer giving usable data in this case.

      Earth is the only speck of dust in the universe where we are certain that there is life. If it's intelligent enough to prosper in the long run remains to be seen. Considering the chemical processes seen in other places in the universe it's likely that life exists elsewhere, but in different forms from what we see here. It would be extremely surprising if we were to find life on an earth-like planet that's similar to us down to the DNA/RNA level.

      What humankind need is to continue to find ways of understanding the universe and how to best utilize the possibilities and circumvent the problems.

      --
      If builders built buildings the way programmers wrote programs, then the first woodpecker would destroy civilization.
    4. Re:In effect, what they are saying, is by Anonymous Coward · · Score: 1, Interesting

      I've said this before, but: use gravitational lensing for your "lens". Put a telescope at the "focal point", point at the sun, and null out the sun itself from the pictures you take - now you have a "lens" the size of the sun. Too bad the relevant point to put the telescope is at 500-1000 AU.

  2. Wrong Approach? by vigmeister · · Score: 2, Interesting

    IANA Astronomer, but perhaps it may be prudent to start looking at the more obvious candidates in terms of how conducive they are to human habitation and evaluate them in terms of what it'll take to make that possible. If an alternate habitat for humans is a moderately serious concern, why bother looking at worlds whose characteristics are under heavy risk of changing by the time we get there? Have we even found a better candidate that one of Jupiter's moons or Mars?

    Cheers!

    --
    Atheist: Buddhist in a Prius
    1. Re:Wrong Approach? by Neon+Aardvark · · Score: 2, Interesting

      As it stands, we're never ever going to get there.

      For interstellar colonization you need either: 1. Artificial wombs and frozen sperm/eggs 2. Colossal generation ship (impractical and very depressing way to travel) 3. Cryogenic storage of humans 3. Self-reproducing sentient robots (humanity wouldn't be spread, but intelligent life would).

      And the ability for humanity to spend ass loads of money on something which they certainly won't see a return on in their lifetimes.

      --
      Azural - instrumentals
    2. Re:Wrong Approach? by gurps_npc · · Score: 2, Interesting
      I call stupidity.

      You left out the answers of:

      4. Human lifespan expanded to over 1,000 years. Frankly, this is easier and more likely to do than #2 or #3.

      5. Many many set of short hops. Alpha Centauri is 4 light years away. An antimatter powered ship can reach 0.1 C. It only takes 40 years to get there. That is one generation, not multiple ones.

      6. FTL travel. Sorry, but no I don't fall for the "we don't know how to do it, so it must be impossible" stupidity that prevented people from trying things like travel faster than the speed of sound. Do you know many people smarter than you thought we could not reach the moon? Lose your arrogance and admit that you don't know everything about how the universe works.

      --
      excitingthingstodo.blogspot.com
    3. Re:Wrong Approach? by Neon+Aardvark · · Score: 2, Interesting

      I'm afraid I call stupidity on you, sir.

      0.1 C as a peak velocity does not equal 40 years travel time to go 4 light years. Can you figure out why?

      Short hops would be a pretty stupid way to travel for the same reason.

      Additionally, antimatter is not a feasible fuel source given the immense cost, and the output (getting momentum out of hard gammas), and the storage difficulties. I'd like a source that shows antimatter can be contained using less energy then can actually be extracted from it - it's not clear that even this is possible. Also, any slight deviation in containment causes a runaway loss of containment, and boom - no more spaceship.

      Anti-matter catalyzed nuclear propulsion is different (maybe).

      RE FTL - I never said I know everything. On balance, given what I do know, it's never going to happen.

      --
      Azural - instrumentals
  3. Wow! by Jane+Q.+Public · · Score: 2, Interesting

    Two huge issues in as many sentences.

    There is no logical reason to assume similar development, barring further evidence. That could be a good or bad thing.

    But your second sentence... wow! Where do you get off making an assumption like that? First, if they have anything like "a pervasive machine intelligence", then their technical development would be VASTLY beyond ours. We are not even remotely close to anything like that.

    Second, even if they did, how in the world do you conclude that would be "less distressing"?? One does not follow from the other.

    1. Re:Wow! by palegray.net · · Score: 2, Interesting

      First, if they have anything like "a pervasive machine intelligence", then their technical development would be VASTLY beyond ours. We are not even remotely close to anything like that.

      In my view, I have good reason to believe we're much closer to that than most people would like to accept. Many reasons, actually. It's probably a normal side effect of human vanity that we take comfort in our present position at the top of the intelligence curve, but I think it's an inescapable fact that future historians (in whatever form they might take) will describe humanity as a species that was destined to outdo itself. To me, what occurs after that will be the most interesting chapter in the history of the human race.

      --
      512 MB RAM, 20 GB disk, 200 GB transfer, five datacenters. $19.95/month.
    2. Re:Wow! by Jurily · · Score: 3, Interesting

      Second, even if they did, how in the world do you conclude that would be "less distressing"?? One does not follow from the other.

      Well, duh. If they have advanced AI, they probably have internet as well. Which means we can view alien porn while we're being wiped out.

  4. Space race across the divide by DigiShaman · · Score: 2, Interesting

    Let's just assume for a moment that a 2nd Earth was discovered with life an all. Would this be a turning point for actually dropping vast amounts of money in R&D for interstellar travel? Iâ(TM)m talking about developing some really exotic technologies ranging from point-to-point FTL travel to wormhole-like jump drives.

    If the laws of physics permits, such a discovery might be what provides the justification for investors and government agencies alike.

    --
    Life is not for the lazy.
  5. Important distinction: by RyanFenton · · Score: 3, Interesting

    There's an important distinction between it being hard to find an earthlike planet, and there not being an earthlike planet to find at all.

    Our mechanisms for finding planets are all in wobbles in the wavelengths from the light of stars. And because of that, we tend to only see the big wobbles, because small wobbles tend to get lost in the noise.

    It would be nice if we could shine a flashlight and get a real look out there, but in most cases, we'd never see what we shone light upon in our lifetimes.

    The universe is a HUGE freakin place, filled mostly with stuff we can't get a good clear look at yet.

    Entire worlds like ours are are both all we know, but at the same time, are too small for us to even notice in the grandness just outside our atmospheric window.

    Ryan Fenton

  6. Re:NASA needs to latch onto this. by Anonymous Coward · · Score: 1, Interesting

    While FTL travel would be a very big step for us, it'd likely be easier to just try to terraform Mars and maybe one of Jupiter's moons rather than setting our sights on things 20 light years away.

    If we started now, given the exponential rate of technology growth, we could probably have cities on Mars within a couple hundred years, and not even the domed variety.

  7. Bullets vs. Energy beams by firmamentalfalcon · · Score: 3, Interesting

    Bullets hurt people because of human blood circulation (loss of blood) and the size of our organs (heh). If robots were built differently or little green men evolved differently, bullets would most likely be ineffective. There is no reason that there is only one wire connecting processor to leg and opening one loop should not hurt the other parts of the circuit. Also, there is almost no reason why the processor needs to be 15 cm big, or the leg motor has to take up the whole length of the leg. There is also no reason why the robots or green guys have to be human size.

    However, as long as they are still made of molecules, high amounts of energy should still be able to separate the molecules that they are composed of, and hopefully eliminate them.

  8. No Princess Lea ... no twin-earth by noshellswill · · Score: 0, Interesting

    ... no byte-boyz fantasy worlds. It's only us alive, palsy. Only we are aware ... of the nothingness that surrounds. The entire rest of the universe is dead cold rock. Surrounded by dead cold gas. Surrounded by a dead cold vacuum of whatever ilk. Have a nice day.