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Space Science

Terrestrial Planet Finder 168

Posted by timothy from the idea-flagpole-getting-full dept.
solarlux writes "The Terrestrial Planet Finder has taken one step closer to reality as two architectures have been approved by NASA. The first, TPF-c, will be a single optical telescope which employs a coronograph to block starlight for planet detection. TPF-i will be a flotilla of infrared telescopes flying in formation to form a interferometer. TPF-i will analyze the planets identified by TPF-c for life signatures. The telescopes are to be launched within the next 10-15 years."
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Terrestrial Planet Finder

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  • Terrestrial Planet Finder (Score:3, Funny)

    by Kenja ( 541830 ) on Wednesday May 12, 2004 @09:18AM (#9126246)
    My Terrestrial Planet Finder...

    (looks down at the ground) Found one!

  • 10-15 years? (Score:3, Interesting)

    by Power Everywhere ( 778645 ) on Wednesday May 12, 2004 @09:18AM (#9126249) Homepage
    By then SETI might have actually found something. Remember, it intelligent life isn't dependent on a planet. Any advanced race probably left their world eons ago.
    • Why would a race leave their planet? Doesn't seem efficient.

      • Re:10-15 years? (Score:4, Insightful)

        by Paulrothrock ( 685079 ) on Wednesday May 12, 2004 @09:30AM (#9126379) Homepage Journal
        A race would leave their planet for a lot of reasons. There is a ton of resources in space, including rare minerals in the platinum group. Also, there are manufacturing processes that benefit from microgravity, particularly in the making of crystals for electronics. Finally, they'd run out of room eventually, and have to move somewhere.

        But, then again, why would anyone have left Europe in the 1500s? Doesn't seem efficient.

        • Re:10-15 years? (Score:2, Interesting)

          by AviLazar ( 741826 )
          They wouldn't have left their planet though (for those reasons). They might have sent "pioneers" out to expand their civilization. Unless their planet became uninhabitable for some reason, the planet would keep it's inhabitants and those that wanted to travel to the next "destination" would go. However, leaving a planet that is habitable just because is not a good enough reason - it is extremely difficult to do (not just the resources, but trying to convince the people to leave). Unlike Sim Earth I doub
          • Of course some people would stay back. Most of the population of Europe stayed there (99%), but there's always going to be people who want to move away, for any number of reasons. (I can imagine that fundamentalist Muslims would love a place to get away from the pervasive 'threats' to their faith.) Once technology gets to the point where it's safe and cheap enough for ordinary people to move to space, that 1% will leave. Of course, this time it'll be 100 million instead of a few thousand.
    • I think you've watched too many SciFi movies. Sure it's technically possible to travel within your solar system, but it isn't guaranteeded that it is possible to build a spacecraft that will travel to the next start in any resonable timeframe. Warp drives and even near-light speeds make good movie material...
      • If the craft is big enough you don't need a reasonable time frame. Make a self-sustaining colony that gets there in a few decades, or even a century, and it's still viable. We're not talking about trade between systems, just moving between systems. It took 66 days on a teeny boat for the Pilgrims to get to America, but they still came.

        • Generation ships (Score:2, Interesting)

          by tepples ( 727027 ) *

          But if you have a self-sustaining colony in space, why even go to a planet? The difference between 66 days and 660 years is that after a few dozen generations, the inhabitants will probably either forget their original mission or chalk it up to "some old religion." Orson Scott Card addressed this "generation ship" issue in more detail in How to Write Science Fiction and Fantasy.

          • Re:Generation ships (Score:3, Insightful)

            by Rei ( 128717 )
            I think this concept of trips to other stars *necessarily* taking decades, centuries, or millenia is based on a common misconception about the speed of light. Many people view it as sort of an intergalactic speed limit. Not so.

            Picture that you're on a spacecraft with virtually unlimited energy resources, for the purpose of demonstration (yes, I know, even matter-antimatter engines have their limits). You start accelerating. And accelerating. And accelerating. Do you ever see your acceleration stoppin
          • Sure they'll forget what their original mission is. But in any large population you'll have 1% or so who wants to leave. Once they get to where they're going, they can choose to leave everything behind and start a new world (very attractive to some), or to continue on in the ship with everyone they know, which will then spend some generations getting to another star system, or simply drifting around the universe.
    • Or they might have stuck around their, already, developed planet? But the amount of time it takes for the information to travel the message we receive could have been sent ions ago from a civilization that no longer exists... What ever happend to sub space telecommunications? -A
    • If an advanced race left their world eons ago, we would see them. They would be here. 'Eons' is a very long time. With the simplest of sublight colony ships, a race could fill the whole galaxy in a few million years. The galaxy has been around for billions of years.
      • If an advanced race left their world eons ago, we would see them. They would be here.

        They are here: mice (or is it dolphins-- need to brush up on my Douglas Adams).

        Seriously though, pretty egotistical to imagine that an advanced race would have the slightest interest in humanity. Hell, most _people_ have no interest in humanity.

    • Remember, it intelligent life isn't dependent on a planet. Any advanced race probably left their world eons ago.

      I love these two common assumptions that people mistakenly make about efforts to find other life-friendly planets. Firstly, who said we're looking only for "intelligent" life? I'd be tickled if we found a planet with silicon-based bunny rabbits or something. And secondly, who's to say any "intelligent" life we find has to be "advanced" relative to us? Perhaps we will discover some stone-age cul

      • If we discover any intellegent life by looking from Earth, it has to be around our level or more advanced, to change the environment enough for us to notice. Even from say 1 AU away, you'd have a job telling Earth apart from a planet without humans.

        Of course looking at radio waves is a possibility.

        • if we do discover intelligent life on another planet(humanoid or not), won't everybody go nuts? Will suddenly religious people feel cheated, and sci fi nuts rejoice? I think there would be rioting in the streets.

      • Has anyone ever considered the possibility that we might be the first ones, that all other "intelligent" life forms are decades or even eons behind us?

        Someone had to achieve "advanced" first.. what if it's us?

      • planet with silicon-based bunny rabbits


        I for one welcome our new silicon-based bunny rabbit overlords.
    • "Any advanced race probably left their world eons ago."

      Wouldn't they also probably be using point-to-point transmissions to talk to each other? Really, I'd think the only hope SETI has is if the other species is actively trying to find us or we run into a species no more and no less advanced than we are (heavily relying on broadcast EM communications).

  • 10 to 15 years (Score:4, Insightful)

    by bsDaemon ( 87307 ) on Wednesday May 12, 2004 @09:20AM (#9126261)
    to find another planet. 150,000,000 years to get to it. Don't forget that we are seeing things as they used to be! discovering other planets is only has good as our ability to get there, which is nil. Not to mention that they probably arn't even there anymore.

    • Re:10 to 15 years (Score:5, Interesting)

      by Xentax ( 201517 ) on Wednesday May 12, 2004 @09:25AM (#9126328)
      Glad to see everyone staying optimistic about these things!

      Some of us still want conclusive data on IF, and if so, HOW MANY Earth-like planets there are out there - on the theory that extraterrestrial life is more likely to be found if there are other worlds out there like ours (we know *this* system works, we don't know what else *might* work).

      The case for ETI is much stronger if you can show that there ARE many many Earthlike worlds in the universe, compared to the present, where we can say "there MAY be many, with this set of assumptions, or ours may be the ONLY one, if you use this other set of assumptions."

      Xentax

    • Re:10 to 15 years (Score:4, Interesting)

      by pe1rxq ( 141710 ) on Wednesday May 12, 2004 @09:29AM (#9126364) Homepage Journal
      Finding another planet relativly nearby might result in an even bigger motivation to get there.....
      Remember not so long ago te sound barier was seen as unbreakable....
      There have already been planets discovered just tens of lightyears away... They are likely to still exist today.

      Jeroen

    • Re:10 to 15 years (Score:3, Informative)

      by Esion Modnar ( 632431 )
      "Insightful"? More like, Pessimistic.

      Besides the astronomical cost, many would argue against development of starships as a waste of time due to lack of meaningful destinations for said starships.

      Well, this is the first logical step. Find some practical, relatively close targets, then start planning a mission or two. Who knows, we may still be a century from such a mission, but every journey begins with just one step.

      Unlike Columbus or Magellan, we can't just go bumbling around until we hit something,

    • Re:10 to 15 years (Score:5, Informative)

      by kevlar ( 13509 ) on Wednesday May 12, 2004 @09:43AM (#9126491)
      The chances of finding an Earth-like planet "in our neighborhood" is far greater than finding one 100+ Ly away. This is due to two reasons:

      1) Closer planets are easier to detect (for obvious reasons)
      2) The heavy metal content in and around our "neighborhood" is greater than that which exists generally through out the Milky Way. This is because before the Solar System was formed, a massive star exploded seeding the area with heavier metals (iron+ on the periodic scale). These heavier atoms are obviously what makes up the Earth. Without this initial seeding, the solar system would only contain hydrogen based planets like Jupiter. Therefore, our local area is the best place to find heavy-metal planets.

      • Re:10 to 15 years (Score:3, Informative)

        by Xilman ( 191715 )
        Unfortunately for your model, the Sun has orbited the galaxy about 20 times since its formation. During that period, the combination of inital random velocities and perturbation by other stars has well scrambled its initial neighborhood. The stars which are local now are quite likely to have been remote a billion years ago, and vice versa.

        On the other hand, stars which are not more than a few billion years old and which were formed in the disk of the galaxy (as opposed to the bulge or the outlying globu

        • The galaxy is very big and it rotates much like a wheel, rather than a bunch of free-floating points. Our local neighborhood of stars have not drifted so much to the point where they're not still our local neighborhood.
          • The closer an object is to the galactic center, the more orbits it will complete in a given timeframe. So stars, even very near stars, will drift away fairly quickly.

            The exceptions are objects that share the exact same orbital path of our Sun (I would imagine this is rare), or objects that orbit eachother -- like planets, or binary star systems. Those will stay together while orbiting the galactic center.
            • If you've taken any galactic structure classes, you'd know that galaxies spin more like disks than they do like free-floating bodies. This is because of the amount of (baryonic?) dark matter between the stars.

              So while you would think that local stars would drift away quickly, that is not the case. Yes there is stellar drift but not enough to put one star on the other side of the galaxy from another within its life span (without a seriously cataclismic event).
              • Hmm, it's a while since I was in astro but I think you are taking the "rotates like a wheel" analogy too far. It's talking about the bulk properties of the galaxy, not the stars of which it is composed. Yes, the rotational angular velocity stays pretty constant, but this doesn't imply the stars are fixed with respect to each other, or even nearly fixed - it's only an average velocity and there will be a spread of velocities, even assuming they are in the same plane and direction. Just doing a simple-minded
                • The stars are definately not fixed WRT each other but the "rotates like a wheel" analogy is not being taken too far.

                  If the stars were to be jumbled up that drastically in one rotation, you would expect (to some degree) to see galaxies that are fuzzy balls rather than spiral with arms. My understanding has always been that an arm revolves as a whole unless stripped apart by other forces (speaking generally here). If it did not rotate as a whole, you would not see these communities like the stars of the Or
                  • If the stars were to be jumbled up that drastically in one rotation, you would expect (to some degree) to see galaxies that are fuzzy balls rather than spiral with arms. My understanding has always been that an arm revolves as a whole unless stripped apart by other forces (speaking generally here). If it did not rotate as a whole, you would not see these communities like the stars of the Orion nebula.

                    Cool, something to do ... I'm stuck at work at 1am doing a restore on a crashed server :(

                    Well, I had tho
    • A little imagination coupled with forethought is in order here. Once we learn more about what is needed stellarly for 'small juicy rock' planets, we then will be able to find nebulae and fledgling stars with higher probability of fostering these planets. We send our artificially intelligent 'children' to those stars.

      Stop being such a small-minded "ME ME ME NOW ME" monkey.

    • I guess light travels more slowly than I remember. (Score:4, Insightful)

      by Christopher Thomas ( 11717 ) on Wednesday May 12, 2004 @12:20PM (#9128824)
      to find another planet. 150,000,000 years to get to it. Don't forget that we are seeing things as they used to be! discovering other planets is only has good as our ability to get there, which is nil. Not to mention that they probably arn't even there anymore.

      You do realize that with a detection range of a few dozen to a few hundred light-years, we'll be seeing planets as they were at most a few dozen to a few hundred years ago, not hundreds of millions of years, right?

      A laser boosted sail-probe could reach a nearby star system ( 10 LY) within one human lifetime. It would be impractial to send one big enough to carry humans, but an automated flyby survey would definitely be feasible.

  • Planning (Score:5, Insightful)

    by Killjoy_NL ( 719667 ) <slashdotNO@SPAMremco.palli.nl> on Wednesday May 12, 2004 @09:20AM (#9126268)
    I've always been very impressed by the timetables NASA is using.
    It must be an enormous task to plan so many years ahead into the uncertain future, not sure if the funding will be there. /me tips my hat to them

  • Pre-history of a new religious reformation... (Score:5, Interesting)

    by Anonymous Coward on Wednesday May 12, 2004 @09:21AM (#9126277)
    Once these things start piling up spectra. We could get some great surprises. Anyone wonder how things are going to change if they find a planet with a big chuck of oxygen in the atmosphere. Yet more proof that we're not quite so special :).

    • Re:Pre-history of a new religious reformation... (Score:2, Insightful)

      by Anonymous Coward
      If you consider our creation myths as stories about how OUR planet was created, there really is no conflict of interest between this science and modern religion.

      Sure, historically The Church has had a problem with this idea, but modern religious people for the most part believe in science. In the same way, modern people in The South believe slavery is wrong despite what their ancestors thought. It doesn't make them give up their southern heritage completely though.
  • This is a great idea. I only hope the funding would be there to ensure launch of those telescopes. And that it won't be used as an argument against human exploration of space.

  • 10 - 15 years? That's quite a horizon. (Score:5, Insightful)

    by machinecraig ( 657304 ) on Wednesday May 12, 2004 @09:24AM (#9126309)
    IMHO - something planned to happen 10-15 years from now has a great risk of not happening.

    Entirely too much can change. You're talking about a funded project that would have to survive multiple shakes up in Administration (and think of all the Bureaucratic structures a NASA funded project relies on!!!) , not to mention a project that would have to be able to keep it's funding for that long.

    Plus - in 10-15 years, it's entirely possible that technology might make this particular project irrelevant.
    • Most missions of this kind have a long horizon... 10-15 yrs isn't that far away.
    • On the 25th May 1961 President John F Kennedy told Congress: "I believe that this nation should commit itself, before this decade is out, to the goal of landing a man on the Moon and returning him safely to Earth."

      10-15 years isnt much long than the 9 quoted here.

      Sure, it needs massive impotus to continue, but a 10-15 year plan is extremely feasible.

      The other alternative is to make the plans so low key that they slip unnoticed under the noses of whichever government is in power at that point.

    • Re:10 - 15 years? That's quite a horizon. (Score:4, Informative)

      by dtolman ( 688781 ) <dtolman@yahoo.com> on Wednesday May 12, 2004 @10:34AM (#9127017) Homepage
      Almost every non-mars NASA science project of the past 40 years has had a 10-20 year gestation period. So for NASA, this is business as usual for a space telescope - this is pretty much following the same timeline as Hubble, or Spitzer (SIRTF), or the upcoming Webb telescope.

      They usually are quite involved - with the teams having to prove that certain scientific or engineering assumptions are even possible years before designing a prototype. If you poke around the NASA mission websites, they usually have the timelines posted in detail - sometime with monthly goals.
    • IMHO - The TPF is one of the most exciting plans in space exploration, ever (right up there with thorough investigations of the chemically interesting planets and moons in our system). It can answer a whole host of questions regarding planetary formation, not the least of which is looking for the presence of life (including non-earth-like life). Even if it doesn't find any indication of it, the data gathered on how and where planets form will substantially flesh out the variables in the Drake equation [pbs.org] (sp

  • Re: Terrestrial Planet Finder (Score:4, Interesting)

    by manavendra ( 688020 ) on Wednesday May 12, 2004 @09:29AM (#9126361) Homepage Journal
    I'm sure it's important and useful to gather information about the planets and other cosmic objects around us - since they help in understanding how we have come here and how our planet was formed.

    An offshoot of this perhaps also helps us understand the weather, and provides knowledge about freakish changes (high tides in full moon, etc).

    Having said all this, I believe such a terrestrial planet finder is largely an academic pursuit. No wonder there is mention of life-signature searching capabilities in these telescopes, since the masses would be most happy to hear about cosmic neighbours (especially since Mars hasn't proved all that exciting!).
    • since Mars hasn't proved all that exciting

      'scuse me? Within the last 3 months Mars Express resp. the MERs have found on Mars:

      a) water ice in the south polar cap, previously thought to be dry ice only;
      b) traces of methane (!) in the atmosphere;
      c) conclusive evidence for a standing body of liquid water in the past.

      All of which is raising the possibility of at least microbial life on Mars, fossil and/or present, which I find plenty exciting. I know it's not much by the entertainment standards of the MTV

  • Challenges of finding extrasolar planets (Score:5, Informative)

    by klipsch_gmx ( 737375 ) on Wednesday May 12, 2004 @09:31AM (#9126388)
    The question becomes even more convolved once we move outside the solar system, since we now know of a wide diversity of systems, of which our own solar system is only one particular instance. (And perhaps not even typical at that.) We know that there are objects extending all the way down from massive stars [pleaseeat.us] (around 100 Msun) to hydrogen-burning stars like our sun to brown dwarfs to planets. Clearly any definition of a planet must apply not only to our solar system, but also to these extrasolar systems. Some of these systems are much like our own (for instance, they may contain a brown dwarf orbiting a star, or a planet orbiting a star), and some (including a few systems of low enough mass to qualify as a planet) are "free-floaters" -- just sitting out there by themselves in space.

    I think ultimately the question is whether there is a single continuous "initial mass function" of isolated objects or not. The best idea as to how stars acquire their initial mass is that turbulence in the interstellar medium, which exists on all scales, establishes a power-law distribution of initial masses. Every once in a while, you get a very strong shock which passes by inside a giant molecular cloud and forces the collapse of a large region which then goes on to form a massive star. But more typically, you form stars more like our sun. [pleaseeat.us] And just as rare as massive collapses are very small mass ones which go on to form isolated brown dwarfs and free-floating planets. If this model holds up to be true, then we are all mincing words in our definitions of isolated systems, since they are all manifestations of the same universal formation process.

    However, to avoid the difficult question of formation mechanisms, an IAU working group of some of the most respected people in the field established a working definition [ciw.edu] to define by fiat what it means to be a brown dwarf, and a planet. Extrasolar "planets" are those objects orbiting a star which are beneath the deteurium-burning limit -- regardless of how they are formed. "Brown dwarfs" are defined to be those which burn deuterium but not lithium, and "sub-brown dwarfs" (NOT free-floating planets!) are defined to be those isolated objects which do not burn deuterium. Even the working group itself admitted that this definition was not satisfying to a single member of the group, and so it is likely it will be replaced at a later time with something more physically-motivated. The "planet/planetismal/KBO" distinction was pushed back to our own solar system, since it will be some time before anyone sees anything that small in another system.

    Also of interest is the following link, which gives a history of previous claims for additional planetary members of our solar system : SEDS [arizona.edu].

  • TPF-i (Score:3, Informative)

    by JosKarith ( 757063 ) on Wednesday May 12, 2004 @09:33AM (#9126404)
    I've heard of the inferometry plan before - it's basically a fleet of 7 - 11 satellites flying in near-perfect line abreast formation. That coupled with a lot of image processing gives the effect of a radio telescope with a dish the size of the formation. There's some loss of resolution, but it's a massively cheaper way of doing it.
    If they can get the formation steady that is.

    • Re:TPF-i (Score:4, Informative)

      by Christopher Thomas ( 11717 ) on Wednesday May 12, 2004 @12:12PM (#9128695)
      I've heard of the inferometry plan before - it's basically a fleet of 7 - 11 satellites flying in near-perfect line abreast formation. That coupled with a lot of image processing gives the effect of a radio telescope with a dish the size of the formation.

      Close. A radio interferometric telescope works like this, because we can record and timestamp radio signals with timing precision much finer than their period (typically nanosecond-range and longer). An optical interferometric telescope has to actually bring all of the gathered light to one place and do interference directly, as our electronics aren't good enough to do direct signal sampling, and won't be any time soon (timing precision needed is on the order of femtoseconds for near-IR, and still tens to hundreds of femtoseconds for thermal IR).

      This requires _extremely_ good station-keeping for the telescopes, but this is a manageable problem (especially since you don't have to worry about as many vibration sources as you do for earth-based interferometric telescopes).

      Googling for "astronomy" and "optical interferometer" will get you links for the interferometric telescopes that have been built to date. Interesting stuff.

  • OWL (Score:4, Interesting)

    by Anonymous Coward on Wednesday May 12, 2004 @09:39AM (#9126450)
    Check out the ESO's Overwhelmingly Large Telescope .. 100 meter diameter .. resolution of 1 milliarcsecond .. should be able to image the Lunar Lander on the moon when it's built.

    http://www.eso.org/projects/owl/ [eso.org]
    -Johan
    • [It] should be able to image the Lunar Lander on the moon when it's built.

      Thank God! We'll finally be able to shut up all of those moon landing hoax conspiracy theorists!
      • Thank God! We'll finally be able to shut up all of those moon landing hoax conspiracy theorists!

        One would hope that this would but true (dis)believers will say any photo shown as proof of the moon landing is faked. There are people that insist the world in flat [talkorigins.org] and that is alot easier to proove false.

  • Intelligence limitations (Score:3, Insightful)

    by carvalhao ( 774969 ) on Wednesday May 12, 2004 @09:41AM (#9126470) Journal

    As usual, we are impared by our own lack of intelligence. We are going to spend a considerable amount of money building a complex infrastructure to retreive information that is... well... pretty much useless.

    We'll be searching for a planet similar to Earth because we believe all life must come in some kind of carbon-made structure forming an organism that needs water to sustain itself and that releases some kind of carbon substance into the atmosphere. We also believe that life on Earth was possible to to it's "moderate" conditions. YET, we keep discovering ON EARTH new species previously unknown who live in the most extreme conditions.

    So, from my point of view as an engineer... we'll be looking at a science subject without knowing exactly what to look for and without being able to extract any conclusive information. Futhermore, the technology that has to be developed to attain this study is not altogether new. So, no new relevant or important data, no new significant tech... What's the point, then?

    If they need a sugestion on where to spend a couple of billion dollars... why not that not yet fully explored planet Earth, with loads of life that considers itself intelligent?

    • As usual, we are impared by our own lack of intelligence.

      Only too true, and to give this some scientific backup (to avoid this cynicist-label) -> DÖRNER [amazon.com]

      Quote from a review: "Wow - a superb analysis of why we fail even when doing things right!", and I totally agree (I here have the original German version published in 1989 - and it is still topical - well).

      CC.

    • Re:Intelligence limitations (Score:4, Insightful)

      by dtolman ( 688781 ) <dtolman@yahoo.com> on Wednesday May 12, 2004 @10:27AM (#9126947) Homepage
      Pretty much useless? Whats the point?

      This is basic science - its sole purpose is to expand the boundaries of human knowledge. Most great discoveries are by taking a look at something no one has ever seen before. If we never look, who knows what we'll find?

      Furthermore - we only have two earth sized planets in the solar system. Thats two datapoints to understand the past, present, and future of our world. By examining other similiar worlds, it could be great use in figuring out what things could happen to our planet - either now or in the future!

    • Re:Intelligence limitations (Score:4, Insightful)

      by Angry Toad ( 314562 ) on Wednesday May 12, 2004 @10:30AM (#9126974)

      We have exactly one example of an earthlike planet. That's not much in the way of data, true. On the other hand it is an indisputable, actual, real example of life evolving on a planet.

      Parsimony pretty much dictates that before we can consider as realistic other, purely hypothetical modes of life we need to understand the apparent distribution (or lack thereof) of planets with earthlike biomarkers.

      I can come up with all sorts of extraordinary ideas about how life might work on other worlds. So can you. All the same I'd argue that making a survey that specifically looks for conditions which we know for certain can be associated with life is the first and logical scientific step which can should taken on this subject.

      I actually don't understand people having objections to such a survey - imagine finding two or three strongly supported oxygen/CO2/water worlds within a few hundred light years!

  • Why such a small array? (Score:4, Interesting)

    by Gropo ( 445879 ) <groopo AT yahoo DOT com> on Wednesday May 12, 2004 @09:41AM (#9126472) Homepage Journal
    A few years back I (and I'm sure others have done the same) imagined an array of telescopes orbiting the sun in each of the Earth's Lagrangian points synchronized with extremely precise atomic clocks. Wouldn't a 2 AU array allow far better resolution?
    • You are probably thinking about a radio telescope. In that case you can measure the phase of the incoming waves relative to an atom clock. Do the same at a distant location (after synchronising the clocks first) and you can combine the signals with a computer. Remember that atom clocks also have a finite accuracy, so you cannot increase the distances indefinitely.

      With an optical telescope, which we are discussing here, you can't compare the phase of the light to some clock (yet). Therefore the only way to

      • I don't see the difference in feasibility between piping the light directly to a "common combination point" and simply logging the point in time that an image was captured (to a sufficient chronological resolution) and crunching the numbers once those snapshots have reached Earth.

        As I see it, the true issue would be sufficiently parallel physical alignment of the sensors (but perhaps this could also be overcome after the fact with software?)

        • We are talking interferometry here: you have to compare the phase of the lightwaves from the different telescopes. Taking an image only gives information about the intensity of the waves, which is in proportion to the square of the amplitude of the waves. The phase information is lost. Also remember that visible light has a frequency of +- 10^14 Hz, so there is no easy way of comparing that to a clock. Do a first year physics course on (optical) wave mechanics to see the difference.
  • Related to this, as the BBC mentions here [bbc.co.uk].

  • Interferometry in space? (Score:3, Interesting)

    by anthonyclark ( 17109 ) on Wednesday May 12, 2004 @09:50AM (#9126558)
    Could someone explain the difference between interferometry on the ground and in space? I thought that it was used to filter out atmospheric interference in ground-based telescopes?

    Is space based interferometry used to filter out things like dust cloud and gravity distortion?

    The thought of a huge solar system sized array of telescopes is most excellent :-)

    • Adaptive optics (e.g. liquid mirrors, guide stars etc.) which cancel out the wave-front distortions caused by the atmospheres are used on Earth. Interferometry allows you to simulate a much larger aperture with a combination of smaller ones... in space there are no atmospheric effects and you can create very large arrays... result = excellent resolution.
    • As stated by another, filtering out atmospheric interference is done with adaptive optics.

      Interferometry is done to simulate a very large telescope by using a bunch of little ones. Primarily done in radio telescopes (like the VLA, the VLBA, etc.) it can also be done in optical telescopes, but the array must be smaller, since you have to physically bounce the light to a common point to combine it (since you can't accurately measure the phase differences otherwise). Still, you can get a 100 m+ sized optical

  • I'm curious... the article mentions that TPF-i will be a corroborative effort with the ESA. ESA, however, has been planning a similar endeavor named Darwin [esa.int], which was to be a flotilla of eight infrared telescopes. So is the ESA folding their Darwin effort into TPF-i? If so, what will be the final name? If they settle on "Darwin", I imagine there might be an outcry by the American fundamentalist camp.

  • Some details (Score:5, Informative)

    by photonic ( 584757 ) on Wednesday May 12, 2004 @10:24AM (#9126911)
    I am somewhat involved with the European version of these missions (the Darwin [esa.int] mission, to be launched around 2014), so I might clear some things up.

    Goal: to detect earth-like planets around other starts. Extra-solar planets detected thus far are usually 'hot Jupiters': big planets that orbit the star in a few days. These are relatively easy to detect. Detecting an earth-like planet (which have not been found yet) is far more difficult. It is usually compared to detecting the light of a firefly (reflection of the planet) flying very close to a lighthouse (the star). Measurements need to be done in the far infrared because there the ratio between the planet and the starlight is the highest (but still only 1:10^6 !!). With some luck they might find traces of ozone and CO2 in the spectrum that might be an indication for life.

    Methods:
    -Coronography: Simply put it is just a conventional big (~10 meter) telescope with a shadow mask that blocks the light of the star. The light of the planet should get past the mask on the detector.

    -Interferometry: Somewhat similar to the techniques used in radio astronomy [nrao.edu]. The resolution of a telescope improves by increasing its size. The trick is to combine several small telescopes. The resolution should then be comparable to the resolution of one big telescope that is as wide as the separation between the small ones. With radio interferometry you can do the 'beam combination' by computer. In optics however you have to physically combine the beams of the different telescopes. This requires flying satellites in formation with stabilities on the order of nanometers!! Current schemes are limited to several hundred meters. There are also some attemps to do this on earth [eso.org].

    There is quite a lot of politics going on between NASA and ESA at the moment about how they should cooperate. First ideas where to do an interferometry mission together, but now NASA has decided to go for coronography and postpone interferometry to 2020. ESA is sticking to interferometry.

    • Re:Some details (Score:3, Interesting)

      by johnjay ( 230559 )
      From what little I understand of interferometry and the planet finder, the most difficult task is stabalizing the formation of telescope satellites. Once that can be done reliably, is it possible to add new satellites after the initial formation has been put in place? It seems reasonable to me that you could upgrade the telescope 5 years after launch by sending up another array of satellites that would combine their efforts with the initial group.

      Is that something we could expect during the life of the pla
      • Yes, but the success of interferometry is based on the distance between two observation points. So to achieve better performance you would only need to extend the distance between the observation points, rather than throw more satelites at it.
        • to achieve better performance you would only need to extend the distance between the observation points, rather than throw more satelites at it.
          D'oh! At the back of my mind, I knew this. But I didn't think about it when speculating. So, in some ways, the idea I had is unnecessary.
          However, shouldn't more satellites in formation provide better imaging? Not better in terms of higher resolution, but better in terms of more information at a given resolution?
          • I'm not sure, I would assume it would (I've never used an interferometer myself).

            On a related note, interferometers in space are actually not a new thing (supposedly). The NOSS Trio are a set of 3 satelites operated by the Navy and is used to detect ships and the wakes they produce, even at extremely deep depths (supposedly). You can see them in the sky flying in formation. Its really pretty cool.

            NOSS Trio [google.com]
  • It's not an earth size planet - but this is prettty cool. BBC News - link [bbc.co.uk] "The historic first image of a planet circling another star may have been taken by the Hubble Space Telescope."
  • As someone said - "xenobiologists are good at designing experiments to look for xenobiologists". Who says you need terrestrial planets for life?

  • Coronagraph? (Score:3, Interesting)

    by Theaetetus ( 590071 ) <.theaetetus.slashdot. .at. .gmail.com.> on Wednesday May 12, 2004 @11:18AM (#9127779) Homepage Journal
    The SOHO telescope uses a coronagraph to block out the sun so it can observe the corona (hence the name). But in the case of SOHO, the sun is taking up a large amount of arcseconds. With a telescope looking at a distant star, would it have enough resolution to have a coronagraph block the star without blocking the surrounding planets? Also, how big physically would the coronagraph need to be (or how small, rather, to only block out the star).

    -T

  • Getting better at interstellar visualization brings back memories of playing Masters of Orion. Is it all coming true now?!

    Now we need to get rolling on the impulsion stuff once we got the visuals going...

  • Sweet! (Score:3, Funny)

    by lonesome phreak ( 142354 ) on Wednesday May 12, 2004 @12:18PM (#9128807) Journal
    Maybe we'll find the planet that the Mexican UFO's [canoe.ca] are from!

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