Two Telescopes Linked To Find Planets 103
glinden writes: "Two telescopes at the Kech Observatory have been optically linked to form the Keck Interferometer. The resolving power of this combined telescope will apparently be sufficient to see earth-sized planets around nearby stars." quoll contributes a link to NASA's own version of the story, too.
Re:Just the start (Score:1)
Gemini will not be an interferometer. For interferometry, you have to know the distance between the telescopes to an accuracy smaller than the wavelength used. Another thing is that you should either combine the beams from both telescopes, or get the phase information of each photon. In radio, it is possible to get the phase information. In optical, Keck and VLT can combine the beams. For Gemini, this would need quite a lot of optical fiber ;)
The main goal of Gemini is to have identical state-of-the-art systems for observing both northern and southern sky.
IMHO X-ray astronomy is much more interesting, but I fear it will take some time before we get the X-ray interferometer, but I have heard some rumours on it.
Re:Interesting, but potentially disappointing (Score:1)
I'm not quite sure how to take that, QPT. I agree that the possibility for extraterrestrial life is a little slim, but there could be billions and billions of planets out there. Each planet makes such a discovery just a little tiny bit more likely. Besides, I'd rather have telescopes taking pretty, scientifically interesting pictures of space than pour more money into military research.
The real distressing partof your comment is re-introducing creationism into schools. You know, as much as I applaud the encouragement of religious fanaticism. . .
Re:Just the start (Score:2)
It is interesting to speculate on how one might do real long baseline optical interferometry, by
analogy with the techniques used in radio astronomy. Essentially you would need to record the phase of the incoming light at (point in the image of) each telescope as well as its intensity. This phase calculation would need to be stable over the duration of the recording, requiring something like a laser whose phase didn't drift by more than a few femtoseconds per hour -- a clock accurate to 1 part in 10^18 or so. This will give a rather large (petabytes/second/pixel) dataset.
Once you have done that you need to track the relative movement of the two telescopes to within a fraction of a wavelength, which will require allowing for the Earth's rotation, tidal distortion, thermal expansion and contraction of the rock, special and general relativistic effects from the Earth's rotation and gravity and probably much more. A better approach might be to observe a known source near the target star and try and calibrate from that. Using three or more telescopes also helps.
Then it just comes down to a comparatively well-understood, if enormous, computing task, to combine the datasets from all the telescopes and synthesise an image.
Only 2? (Score:4)
COAST [cam.ac.uk] has five in it's array. It's first images [cam.ac.uk] were made in 1995.
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When will we hear a scientist say... (Score:2)
Disclaimer: I know they can't detect Death Star sized objects with this. That is, not until its too late!
Been done before (Score:2)
Re:Just the start (Score:1)
question.. (Score:1)
_ _ _
I was working on a flat tax proposal and I accidentally proved there's no god.
Re:Why didn't they do this before? (Score:1)
Also they have to keep the temperature of the whole system itself stable, or the beams will flex, and again distort the image.
Speed (Score:2)
Good Optical Interferometry Article (Score:2)
Re:Just the start (Score:1)
--
If the good lord had meant me to live in Los Angeles
Re:Caution (Score:1)
Re:3D Glasses!!! (Score:1)
"What's that lump there? It looks like a red pill." .. "no, I think it's a blue pill..."
Re:Just the start (Score:2)
Just a tibit of correction. The VLT is not in New Mexico. You're thinking of the VLA - the very large array, run by the National Radio Astronomy Observatory. The VLT is in Chile and run by the European Space Organization.
The VLT is an optical telescope, and they are designed to do optical interferometry with 4 telescopes, but I'm not sure that this has been done yet. The VLA is an radio telescope, and interferotetry has been done with radio waves for decades. Essentially, the difficulty goes with the length of the wavelenght. I.e. the longer the wavelength, the more room for error you have when you stack the signals. That's why its possible to stack nearly 30 signals at the VLA, but we're only doing 2 or 4 in the optical.
This is really quite an achievement. And no, you don't 'listen' to the radio telescopes like Ms. Foster did in Cotact...
Also, Gemini is a joint project among *many* countries, spearheaded by the group here in the US. I'm not even sure ESO is a part of it. The members are Chile, US, Australia, Brazil, Canada, UK, and Argentina. Please check your facts before you do this sort of ting.
By the way, the OWL is a concept telescope which has yet to be developed and probably won't be for a decade or two. You are right, however, in your general ideas, but bear in mind that even what they are doing at Keck is very difficult, and it will be years before Gemini starts operating as an interferometer (and even so, I'm not sure if it's equipped to do it yet). Right now, Gemini is just starting individual science observations.
It really is an exciting time to be doing astronomy, professional or otherwise.
Re:Interferometers (Score:1)
Sooner or later, I think, we will have a reason to try traveling through space
"Not because [it] is easy, but because [it is] hard." Cynical old bugger that I am, I still get choked up even thinking about Kennedy making that speech. Even though I know on an intellectual level that it's a carefully crafted piece of political manouvering, it touches some deep place that makes me believe that even our lazy, greedy short sighted little race can occasionally reach it's grubby monkey paw to grasp at all that is great and noble and transcendent.
Re:Speed (Score:3)
Sounds easy? Think again!
1.chemical propellents - 10^137kg
2.fission - 10^17kg
3.fusion (inc orion craft) 10^11kg
4.ion/antimatter rocket 10^5kg
First of all, as you point out, a solar sail and a stationary laser would work quite well for sending probes out to other stars (though slowing down at the end would be quite a trick).
Secondly, I question some of these numbers. They're looking at only one range of the problem space - setting a time, and deriving a fuel/cargo ratio from there. The problem with doing this is that the fuel/cargo ratio will start to blow up once the amount of fuel becomes greater than your amount of cargo (it starts taking exponentially more fuel to reach a higher speed, because you're mostly hauling fuel).
A better question is, "given a certain fuel/mass ratio and a certain delta-V, how long would it take to reach Alpha Centauri?". My answers are as follows:
[Velocities and travel times are for a flyby; use half the velocity and double the time if you want to stop at the destination.]
Most of the energy of a matter/antimatter annihilation comes out in the photons (even if you're doing a proton/antiproton annihilation, the mesons get only a small fraction of the energy). Assume a 10% efficient conversion of mass to useful thrust, and thust/energy efficiency of a photon drive (horrible - 1/C N/J).
This could be built as a big block of lead/concrete/rock with the ship and fuel tanks on one side, and antimatter explosions happening just over the other side.
Velocity at 50% fuel: 0.05 C (100 years)
Velocity at 10% fuel: 0.01 C (500 years)
This assumes 1% conversion of mass to kinetic energy within the plasma (still inefficient at this energy density, but much better than photon drive efficiency).
Building a drive like this would be very difficult. You'd have to use one of the fusion reactions that doesn't produce gamma rays or neutrons, you'd need a great magnetic bottle, and you'd have to have your exhaust leave the rocket before it could radiate its heat as light. Good luck.
Velocity at 50% fuel: 0.07 C (70 years)
Velocity at 10% fuel: 0.014 C (350 years)
This assumes 0.3% conversion of mass to useful energy, and photon drive efficiency.
This could be built as a big block of lead/concrete/rock with the ship and fuel tanks on one side, and fusion bombs being set off in space on the other side (counting on the plasma radiating most of its energy as light before dispersing).
Velocity at 50% fuel: 0.15% C (3,300 years)
Velocity at 10% fuel: 0.03% C (16,700 years)
As with Good Fusion, but with 0.03% mass to useful energy conversion. Ship design is similar to Good Fusion.
Velocity at 50% fuel: 0.015% C (33,000 years)
Velocity at 10% fuel: 0.003% C (167,000 years)
This assumes 15 MJ of exhaust kinetic energy per kg of fuel. This is attainable with a good chemical rocket.
Velocity at 50% fuel: 0.0009% C (550,000 years)
A really good antimatter drive could bring humans to the next star within their lifetimes, if it was mostly fuel. An excellent fusion ship could do it within a few generations, though fusion ships would more likely take centuries (even if mostly fuel).
Good Start. We Can Do Better. (Score:2)
I've thought of this before, but I didn't think they would do it on Earth. I was thinking that they should launch another Hubble and do it. In space you could easily move the telescopes closer together or further apart.
Of course, this increases the resolving power but it does nothing for light-gathering capability.
The problem is lenses. They simply have to be too big. What could we put in space that would act like a really big lens? The only way I know of to focus light without passing it directly through a lens or bouncing it off a mirror is with gravity.
It simply isn't practical for us to built a gravity telescope.
Is there anything else that will bend light? If we could create a large "light bending field" in space, we could get a lens the size of a planet. We would just have to be careful that we didn't put the Earth in the focus. Then again, maybe the Ant People from Andromeda are already planning to do that to us.
Re:Why didn't they do this before? (Score:2)
Just a thought.
Re:Correction: Earth-like planets NOT detectable (Score:1)
Imagine (Score:1)
Sorry, I had to say it.
==>Lazn
Re:Symmetric Multi-Telescoping (Score:1)
Couldn't resist!
Re:on a volcano?! (Score:1)
Re:Why didn't they do this before? (Score:1)
My nutshell is very course.
Just the start (Score:4)
But the next leap forward is going to be European... ESO (European Southern Observatory) are constructing two identical telescopes in Chile and Hawaii [gemini.edu] (project Gemini.) How's that for a long baseline? [gemini.edu] ;p
And for bluesky "gee whizz" quotient, check out the Overwhelmingly Large Telescope (OWL) [eso.org]...
I've seen a chart somewhere (can't find a link - anyone?) charting aperture (light collecting capacity) of telescopes since Galileo. The Keck and other 10m class telescopes have moved the curve from a nice straight line to an exponetial curve - and that's not allowing for vastly increased computer power, active optics, and out-of-visible band stuff. Truly this is a fantastic time to be interested in astronomy [astronomy.com], even (especially?) as an amateur [skypub.com]. For a couple of thousand dollars you can do stuff in your yard that was the province of professionals only a few decades ago.
--
If the good lord had meant me to live in Los Angeles
Re:Just the start (Score:1)
It is already too late. AAMOF a lot of the new telescope tech was developed in the "black" by military scientists.
Case in point: Adaptive optics. You know, you can use a telescope the other way too: placing a light-source, such as a high-power laser, at the focus and using tho optics to collimate a sharply focused beam to destroy aircraft, missiles or satellites with. But the turbulent atmosphere messes up your beam and disperses the energy. Thus adaptive optics, where a small laser constantly measures the distortion and a "rubber" mirror exactly compensates for it in real-time.
/Dervak
Re:Too damn cool (Score:1)
The two Keck telescopes were not built simultaneously.
Keck I had seen first light and had already been in operation for quite a few years (IIRC)
before they started construction of Keck II beside it for the specific purpose of inteferometry.
optics (Score:2)
Re:I wonder... (Score:1)
Re:Speed (Score:1)
yes they do. An orion drive is nothing more or less than a primitive nuclear rocket, and not a very efficient one at that. You still have to carry fuel & reaction mass.
This site [nasa.gov] has some relevant information. One question that is answered is "How much propellant mass would it take to get an object the mass of a space shuttle/bus past alpha centuri within 900 years"
Sounds easy? Think again!
- chemical propellents - 10^137kg
- fission - 10^17kg
- fusion (inc orion craft) 10^11kg
- ion/antimatter rocket 10^5kg
Unless we pick up fuel on the way with some kind of ram jet, use an external power source (laser sails), or invent something *radically* new, we ain't going anywhere outside this solar system.AFK the orion craft was designed for missions around the region of jupiter, not interstellar flight.
Re:I wonder... (Score:1)
Re:Interferometers (Score:1)
No, O2 has no prominent absorbtion band in the IR wavelengths that is going to be used. However, O3 (Ozon) is an extremely reactive chemical, and its presence implies that there is O2 (that can be dissociated by UV radiation and recombine to O3).
So, if you find O3 there has got to be O2 too.
/Dervak
Re:Can't Really "See" Them (Score:2)
Essentially the researchers used very sophisticated image processing software to detect this "signature" pattern of colour and brightness variations in the light of the star (before processing the signal was 20000 times fainter than the noise). They can't point to any one photon and say "this is reflected light from the planet" but they can say statistically that reflected light is almost certainly present in their data.
Re:Interesting, but potentially disappointing (Score:1)
Looking for new planets is a singularly boring endeavour. Who wants to put on headphones and listen for voices in the static coming in?
If there were aliens, we would have been visited already. After all, if time travel were possible, why has nobody ever visited us from the infinite future? Even if nobody in the next thousand years visits us, somebody in the next million years ought to, and any sane person would surely agree.
Obviously, we are alone in the universe.
But try and tell that to the liberals. Your biblical truths are right on the money. God wasn't just stroking himself when He created this planet, and we should recognize this when we spend those billions of dollars on telescopes. Perhaps then we might find some wisdom and put the money into Christian Bible academies.
--
clarity... (Score:2)
Correct me if Im wrong (im sure you will all have no problem with this request) - but we are not going to be capable of imaging the actual planet body but instead be capable of detecting the influence of smaller planets on their stars...?
Imaging an actual planet is very different from detecting wobbles in Star orbits... where the former is surely the 'holy grail' our planet needs to motivate - and provide perspective to our opportunity in the universe - and work towards a real and noble goal of establishing a permanent, self-sustaining, Human presence other than Terra.
Re:on a volcano?! (Score:2)
Not only is Mauna Kea not likely to ever erupt again (see the "hotspot" explanation posted elsewhere), but my understtanding is that the site offers some of the most uniformly best seeing available within the US borders, due to its elevation, the smooth air flow off of the ocean (minimizing "twinkle"), and the distinct absence of light pollution. Not only that, but its proximity to the equator offers views well into the southern celestial hemisphere, allowing observatories based there access at one time or another to nearly the entire sky.
Even if there was a real risk of the volcano erupting, I'd still be very tempted to stick a telescope or two up there....
-- WhiskeyJack
second? (Score:1)
Symmetric Multi-Telescoping (Score:4)
Re:Interferometers (Score:1)
Not by a long shot... (Score:1)
on a volcano?! (Score:1)
maybe i'm a pessimist here, but what happens if that 'dormant' volcano decides to wake up? WOuldn't that be a helluva large amount of lost money and equipment? I'm not American, but I really question the wisdom of putting an expensive lab on top of a volcano.
"It's dormant! Really!"
How many times have we heard THAT one before?
Why didn't they do this before? (Score:2)
College hasn't healed a genetically predetermined boneheadedness, it seems. ^_^
---
Sorry, fogot my paragraph tags... (Score:1)
That MAY be true if the reason for finding and imaging planets were to find extreterrestrial life, but it's not. That would just be the cherry on the cake.
It is to get a better understanding of how our own planet came into existence, to learn more about how the universe is comprised, etc...you know, REAL science. Are you saying that finding other solar systems beyond our own isn't important?
Sedondly, to say that a magical mythical god created life, when science has proven [msnbc.com] that we evolved, would be a tragedy. To stop all learning because God and the bible provide all answers would be a blow to discovery, BIG TIME. The Bible is a Christian book, what about all the other religions? Religion is required by the fact that every human being longs for the answers to questions of, "Where did we come from?", "Where are we going?", and "Why am I here?". Religion (whichever one you have been TOLD to choose by your social surroundings) answers all these questions nicely, and for that purpose.
What would happen if we suddenly were to realize, that we are NOT alone in this vast universe. A universe that is so vast, that most humans can't comprehend the size and distances involved. What would happen to your religious beliefs? To find out that we are not only NOT alone, but that we are relatively young in the universal intelligence pool. What then?
We live an a non-descript planet in the middle of a non-descript solar system in the middle of billions of stars that make up our Milky Way galaxy, one of billions of galaxies...and you're going to tell me that we are it?!?! Shame on you for your egocentric ideals. To project the hint that you KNOW that we are alone. Are you the ALMIGHTY god?! I think not, and no, you DONT know if we are alone, you couldn't possibly know, so why do you say these things??? We are finding the building blocks of life [sciam.com] in deep "empty" space! So to say, that in trillions of tries, where live giving particles are found in all areas of space, just happened to evolve on OUR planet for no apparent reason (sarcastic), would be silly. To say that in the 20 billions years (our guess as of today as to the age of our universe) that our universe has been evolving, that Earth was the only place that life arose would also be rather simple minded. By the numbers alone, as stated by the Drake [seti-inst.edu] equation, to say that we are alone goes against the odds.
Lastly, just because Mr. Alien hasn't walked up to your door and introduced himself/herself (PC) to you, DOES NOT constitute proof that we are not being visited on a very regular basis, now is it. To say that we will never be able to travel faster than the speed of light is also extremely narrow minded. We (well, other scientists actually) are now sending light at 3 times 186,000 miles a second, not to mention, we have STOPPED light, and then sent it on its way. To say that manipulating gravity wouldn't bypass the speed of light conundrum is also wrong. To warp gravity is to also warp time and space. We can concievably travel vast distances in a relative instant, all within the realm of reality, TODAY.
Anyway, my rant is over. I just was blown away by narrow mindedness of some of the responses here. To know that we know LITTLE of the universe we live in seems to be forgotten. To assume (yes, makes an ass out of u and me) that we are it, and that discovery is BORING, is, well, illogical. Thank you for your time...Bartles and James
The real question is (Score:1)
Cavalry Pilot's Reference Page [cavalrypilot.com]
Re:We've only been able to see really big planets (Score:1)
kewl, but (Score:1)
Damn, we need an array of these things. O wait, VLTI. [eso.org]
Interferometers (Score:4)
No, this instrument will not see Earth sized extrasolar planets. Read the article.
This has been thought of before, and not even this past century, but only recently (past 20 years) has the tech been there to actually DO this. The optics and the placement of them, esp in the delay line, has to be quite precise. We're dealing with fractions of wavelengths here.
Basically it works like this: You have two telescopes, and the two light beams are brought together accurately so that they create interference fringes (hence the name interferometer). The interference fringes tell you about the light at a specific spot in the sky, in a very narrow angle (well, a REALLY REALLY narrow angle). From this, maps can be made of spots on very active stars, etc. (None of this is seen directly). Effectively, what you get is the same resolution of a theoretical mirror that's the same diameter of your baseline. You just don't get the light grabbing ablity of that theoretical mirror.
Dim light is the bane of interferometry. In an ideal world with ideal funding, interferometers would be nuked in favor of full sized optics kilometers across, but who's going to foot the bill?
The longer the baseline, the narrower the angle you can see, hence more resolution. Keck is a good start, but the baseline is way too narrow for what people are speculating on this weblog. Maybe someday when someone finds the funding, we'll have a space based interferometer with big mirrors and a few thousand klicks in between for a baseline.
We've only been able to see really big planets (Score:1)
Then we can look closely at radio tx's from that area of space. Maybe we'll find intelligent life. Maybe we'll just find more space for the 6 billion known intelligent lives.
Cheers,
Rick Kirkland
3D Glasses!!! (Score:4)
Can't Really "See" Them (Score:2)
Nothing we have can see extrasolar planets. The planets that have been detected thus far (AFAIK) have all been roughly the size of Jupiter or larger, and were detected indirectly by looking at the motion of the parent star. The gravitational pull between the star and its satellites causes the star to "wobble" from our perspective. That is, of course, only if the system's axis is mostly perpendicular to our viewpoint. If it's parallel, a doppler shift measurement can be used.
So while the Keck Interferometer may not provide an actual look at a planet, the increased clarity *should* allow us to detect the smaller wobbling caused by smaller orbiting masses (they estimate Earth-sized). At least, that's my interpretation of all of this.
Re:Just the start (Score:1)
I would be extremely surprised if Gemini could be used for optical interferometry, the purpose seems to be more to have complete coverage of the sky. For a start not much of the sky can be observed with both telescopes at once, and also you can't just take two pictures and then combine them. (Well you can, and it'll give you more intensity and slightly more contrast, but no more so than a longer exposure time, there will be no increase in resolution)
This might work with radiowaves as they are long enough to record the phase at both places and then combine them later, but i'd be impressed if they did that at visible wavelengths :). As far as I'm aware the interference is still done optically, thus requiring some proximity between the two parts of the interferometer.
Then again, I don't really have a clue about astrophysics, so i'll just shut up now...
Re:Troll (Score:1)
But ofcourse. Science is the only way to find the answers to our questions.
Re:I wonder... (Score:1)
I agree. It might not be possible with current technology, or technology achievable within 20 years. But do you think that we are trying as hard as we could?
Re:Interferometers (Score:1)
Maybe someday when someone finds the funding, we'll have a space based interferometer with big mirrors and a few thousand klicks in between for a baseline
Or, better yet, we move the optics closer to the target, e.g. by a couple of light years. ;)
Nostalgia isn't what it used to be, but does anyone else remember the days when space exploration was something we went out and did? This story shows a smart use of limited resources, but there's only so far we can go with this approach. And I'm wondering if cheap CGI has put the nail in the space exploration coffin.
I mean, look at the headline, even on /. "Blah blah To Find Planets". When (if) the mass media picks this up, how do you think they'll want to run it? Interferometer patterns and a dry factual piece? Hahahaha. No, they'll show some swooshy CGI of a speculative alien world, while Stacey Implants gasps that scientists are on the brink of discovering alien life. Why bother to make bigger collectors when you can just upgrade your copy of 3D Studio?
I'm (semi seriously) picturing a day when NASA becomes not much more than a huge animation lab and PR machine, with a crew of "scientainers" throwing real data on a slush pile of news bite concepts. Sorry, I don't quite know how I got to Cynical City from a nice article, it's just that it's 2001, and we're still not out there!
Pretty pictures (Score:2)
How long do you think it will be before we can actually see big "high" quality pictures where you could make out features on the surface etc?
Is such a thing possible without actually visiting the system?
Re:I wonder... (Score:2)
I couldn't agree with you more! Many of Terra's problems are because of lack of focus and 'in-fighting' - if the whole world suddenly woke up one day to a 'newscast' saying 'This is the image of another planet that has oxygen, water, and is capable of sustaining us' everything would change! Instantly! It would be like a visit from Aliens. If we could ever show people this - they would stop fighting about Coke-vs.-Pepsi and other 'in-bred-cockfighting' and start thinking for a moment; We can actually GOTO ANOTHER PLANET!
I just hope that someone is able to produce an image of some planet - not a wobble - but an image.
Now, the question is: How do we actually send anything (ourselves even) millions of light years away???!?!! This is the non-trivial part of the problem.
Re:I wonder... (Score:2)
It would take emmense propulsion power to get a craft of any reasonable mass up to near light speeds.
Technically, near-light speeds are attainable with enough propulsion force.
But, there's a lot of crap out there. Rocks and Dust, perhaps, but at those kinds of speeds any stray bits of matter in the way might as well be a brick wall, because they're coming right through the hull of any vessle that hits them.
Supposing you point your craft into the right trajectory, you then have to spend a long period of time accelerating up to the speed. You're THEN going to have to fly at that speed for several years hoping you don't plow right into something like a large rock, or a gravel cloud, or a really slow UFO.
And ONCE you've now pulled off two impossible stunts, you have to go for a third by stopping, which is going to take up just as much power as getting yourself UP to this speed (and let's not even get into the troubles associated with the attitude control of a vessel trying to come down from almost-photonic speeds.)
Then of course you have the superficial problems of keeping those silly humanoid things onboard alive for the journey. Food. Water. Environmental control. Internet Access. It's a real pain.
"Everything you know is wrong. (And stupid.)"
Re:question.. (Score:1)
Re:on a volcano?! (Score:1)
Caution (Score:1)
Re:Interferometers (Score:1)
Thats Ozon, shouldn't this be O2? (Oxygen)
Jeroen
Why Hawaii? Why not West Virginia? (Score:2)
Re:The real question is (Score:1)
Re:Interferometers (Score:2)
Re:we can see the past! (Score:1)
Re:Interferometers (Score:1)
I think part of the problem is that we have no competition from other nations anymore. All we have is cooperation, which is good - except it doesn't drive us. Without competition, there is not much motivation besides curiosity.
Sooner or later, I think, we will have a reason to try traveling through space. Possibly to mine minerals on asteroids or something. We might as well start gaining expertise at it now. Congress, however, is rather short-sighted in this regard. It's always been that way. When Columbus sailed the ocean blue, he was able to get financing from Spain only after promising to find a shorter route to the Spice Islands (I think that's what it was.).
Even if there are no practical benefits to exploring space, I still think we should do it. Do we really take oursleves so seriously, as the human race, that we can't afford to have a little fun and continue to explore the Universe we live in?
How an interferometer works, indirect detections (Score:2)
There are three or four popular methods for looking for planets, and the differences are quite subtle (well, they were to me).
The first method is Doppler velocity detection - the planet and star both orbit about their mutual center of gravity, a point somewhere near the center of the star as the mass of the star >> mass of the planet. The light of the planet itself is not detected, but a spectrograph analyses the stellar light to measure the velocity of the star with respect to the Earth. This is due to the Doppler effect, i.e. the starlight is slightly blue-shifted for the star coming towards us, red-shifted if it's going away.
After subtracting off the eath and sun's velocities, and taking measurements over a few years, a periodic shift is seen in the star's velocity and this is attributed to the gravitational influence of a planet. To date, this is the method that has pulled out all the detections so far.
However, the reflex motion of the star is only about 10 meters/second, and the spectrograph can only detect signals typically bigger than 3 meters/second. Also, only large planets near to the star are easily detectable.
A second method is planet transit - if the orbital plane of the planet is edge-on to the our Solar system, then the planet can move between us and the star and the starlight will dim for a few hours as the planet crosses the sun's disk - the trouble with this method is that you only see planetary systems that are edge on as viewed from Earth. To dats, only one system has been discovered with this method, and even that one was suggested by a Doppler velocity search.
The third method is a variation on interferometry called 'nulling' interferometry, and relies on the wave nature of light. AFAIK, the Keck interferometer is quite a way off achieving this sort of performance, but the trick here is that the light from the two telescopes are combined in such a way that the starlight cancels out but the starlight reflected from the planet's atmosphere is not cancelled out.
One way of thinking of this is looking at a car's headlamp and a bicycle lamp next to each other, and then looking at them through a picket fence. By moving your head laterally you can get one fencepost to block the car headlamp, and get the bicycle lamp light to shine through one of the gaps. The separation of the two telescopes then determines the effective pitch of the fenceposts.
Re:Only 2? (Score:1)
Unfortunately, they are small telescopes. When you are doing interferometry, bigger is better because you toss so many photons out the window.
Palomar has an interferometer, and they have/are working on one at Mt Wilson. The point with Keck is not that you will have an optical interferometer, but rather you will have one you can use from planet searches. Good luck doing that with 1 meter telescopes.
COAST is amazingly impressive, though. Typical Brits, great instruments, crappy site.
Re:Why Hawaii? Why not West Virginia? (Score:1)
Re:The constellation (Score:1)
and..? (Score:2)
Re:Just the start (Score:2)
You raise a good point, though. I am curious about their plans for AO on such a large scope -- I've always understood this as a fundamental limitation, independent of the technology involved. (Err, you sound like you're almost certainly aware of this, but : Each point on your secondary corresponds to multiple points on the sky, but the mirror can only be in one place at a time. thus, you can only correct for one of the real-sky positions which maps to a given spot on your secondary. This isn't a big deal if you have a small scope, but when you talk about going over 20m, I really don't see how you can get around this, since atmospheric variations occur on scales smaller than this.)
Re:Interesting, but potentially disappointing (Score:1)
Re:optics (Score:1)
The clever bit is that if you have two telescopes hooked up with interferometry, their effective aperture is equal to the distance between them. For radio telescopes, this has been used to create telescopes "as large as the Earth". It's a much harder thing to pull off in visible light wavelengths because of the precision required to align the telescopes.
Re:Interferometers (Score:1)
We're not out there yet because it's very, very difficult. There is still a lot to learn about human physiology (and psychology) in space, for starters. Never mind the techno-engineering required.
Selfishly speaking, I would love to see a manned expedition to Mars in my lifetime. But there's a lot of other things that need doing, and only so much time, talent, and $$$.
And frankly, what are the payoffs? Mostly "only" scientific. No, you're not going to alleviate the population pressure on Earth by shipping people into space - that's absurd. We can breed 'em much faster than you can launch 'em :-) And it's much cheaper and easier to optimize resource use and recycling than trying to implement such engineering wet-dreams as "mining the asteroids" and such. Mining the asteroids will be useful for those who build the space habitats, though. Just not right away.
Yes, it will happen... it's just a lot, lot tougher than most /.-ers seem to think.
Re:on a volcano?! (Score:1)
This is just the beginning... (Score:1)
Just wait until they work their way up to building this [nasa.gov]. Then we'll really start seeing the good stuff.
Correction: Earth-like planets NOT detectable (Score:4)
The resolving power of this combined telescope will apparently be sufficient to see earth-sized planets
Whereas the article says:
The Keck Interferometer will be able to detect planets farther from their parent stars, helping to pave the way for future interferometers in space that will look for Earth-like planets, NASA said
To find Earths (at least directly) you have to go to space [nasa.gov] Don't expect this for another 10 years or so.
Too damn cool (Score:1)
Or is this like the time that the NYTimes reported a spun mercury reflector as high-tech?
Actually, I'd imagine the linkage itself is the high-tech part; the sort of deal where astronomers have wanted to do this for ages but actually hooking the thing up was beyond the ken.
Nyarly is going to stop thinking out loud now. Alternatively, consider this a request for more info...
Re:Why didn't they do this before? (Score:1)
I wonder... (Score:3)
Space exploration has, to some extent, died off. We spend a lot of time heaving new shiny things into orbit, but we don't seriously talk about new colonies or settling other planets.
I wonder, if this telescope spotted an earth-sized planet, suitable for life, with an earth-like atmosphere, would space research undergo a rennisance? Would the idea that "we can go there!", with a very specific there in mind, a there you could point at in the heavens, somehow inspire the human race?
Ultimate web cam .. was - Re:Turn 'em round (Score:1)
Other than the obvious financial constraints, is there a law preventing you from putting your own 'scope in the sky??
The possibilities are endless...... talk about the ultimate webcam.
The thought of big brother keeping an eye on my every movement 24/7 does scare the shit out of me though.
Re:Interferometers (Score:1)
Besides this, a nulling interferometer gives you an image with two spots for each planet. One is in the real position, and the other one in the mirror-reversed by the star position. AFAIK there is no way right now to find out which one is the correct one.
So, the Keck interferometer will probably not be able to see terrestrial planets around other stars (altho it will be able to see Jovian ones, including ones far from their star, which should complement radial-velocity searches nicely). The proposed Terrestrial Planet Finder [nasa.gov], consisting of four 3.5 m mirrors in space separated by a baseline of up to 1000 m, working in IR (3-30 um) would not only be able to detect Earth-sized planets, but take their spectra and detect absorption bands from H2O, O3 and CO2, that is, detect the presence of life.
/Dervak
Re:Just the start (Score:1)
This is the start of what??
Man's conquest of the air also began with weather/observation balloons, and just look where we are now.
How long before star wars really become star wars.
If history is anything to go by, then you should be worried... really worried.
Re:Just the start (Score:1)
Back on-topic, the keck interferometer is a huge achievement. Getting such a long baseline at optical wavelengths is hugely impressive - this is roughly equivalent to keeping the two posts the same distance apart to within 20 cm - when one post is here, and the other is on the moon!
Re:Why didn't they do this before? (Score:2)
In practice it means that your mirrors have to be aligned so precisely, that if you scale the whole telescope array up to the size of the US, the positioning would have to be flat and constant up to a scale of meters (or feet).
Re:Can't Really "See" Them (Score:1)
Umm....maybe. After this "direct detection" was announced, [lanl.gov] another group, with BETTER detection capability, failed to find the claimed signal. [lanl.gov]
The original group then admitted that the supposedly directly detected planet was not so bright [st-and.ac.uk]
Why all the controversy?
the signal was 20000 times fainter than the noise
Repeat:
the signal was 20000 times fainter than the noise
More than you ever wanted to know about this star [harvard.edu]
----
cliamer: IAAPA
Re:Just the start (Score:2)
Just in case you read repies: you're right in what it would take, but it cannot be done.
The problem is related to the Heisenberg principle - "light" behaves as a much more quantum phenomenon than radio waves do, since radio waves have much longer wavelength. For the same total energy (E=n_photon*h*c/lambda) there are many many more radio photons (by the ratio cm/nm = 10^7) and so radio waves can be classically detected and amplified without loss of phase info.
Optical photons cannot be detected and amplified without loss of coherence unless you have a laser beam shining at you from a star: so you require HUGE photon buckets (10m Kecks, 8m VLTs) which collect enough photons to share and split amongst themselves for intereferomtry. So radio astronomers can do interferometry routinely, but optically, its very very hard to do.
(Yes, IAAPA - a radio interferometrist, even)
The constellation (Score:2)
Hey, they found stars in my web browser? :-)
Sorry... just found it funny...
Re:on a volcano?! (Score:1)
IANAV (I am not a Volcanologist)
Re:on a volcano?! (Score:1)
For more info, see:
http://www.soest.hawaii.edu/GG/hcv.html [hawaii.edu]
Re:optics (Score:2)
And for the anal-retentive among us, strictly speaking, the above is only approximation. There is considerable complexity in how much resolution the system has (and in what directions). The explanation is meant for those with no background at all in optics.
Re:Correction: Earth-like planets NOT detectable (Score:1)
Keck and NASA are not blood related. In fact, they compete for funding and PR..
I would say that Keck has a different view (ha!) about itself than does NASA..
Re:clarity... (Score:3)
No, the goal of future pie-in-the-sky NASA missions like the TPF (Terrestrial Planet Finder) is to directly image other planets by nulling the light from the star. This is not the indirect wobble detection that Marcy and Butler are doing so successfully [exoplanets.org] on the ground now: rather, you image the planet, maybe as a dot, get a spectrum, and - holy smoke - there's free oxygen in the spectrum!! Life! Little green men! More funding! :)
The Keck interferometer, OTOH - it's not going to resolve small earth-like planets. But its a step in the right direction, and should resolve brown-dwarf companions and maybe giant planets too...
(Yes, IAAAstronomer)
This won't detect Earth-sized planets ... (Score:1)
Assuming NASA survives all the politicians padding their districts with pork while at the same time cutting valid science programs ...
which doesn't seem likely ...
the Terrestrial Planet Finder [nasa.gov] tentatively scheduled for 2011 will be the mission that actually detects, images, and analyzes light reflected by Earth-sized worlds within 50 ly of Earth.
The difference between observations made by Keck, those made by SIM, and those made by TPF will be comparable to the difference between the telescope used by Galileo, the telescope used by the average small college observatory, and the Hubble.
Re:clarity... (Score:1)
Imagine when the first super interferometer scope images an earthlike planet. They see land masses, and oceans. They see lights on the dark side (beyond the terminator) of the planet. They analyze the light from the dark side and find three primary elements in it: Tungsten, Sodium, and Mecury. That would be proof of inteligent life. (Because those three elements are found in the light from every common electric street lamp!).
Re:kewl, but (Score:1)
An array would probably help, but the surface of each telescope mirror acts a little like an array all on it's own. Since each telescope is individually one of the largest in the world then they get a very effective array without needing lots and lots of telescopes. I think that a couple of large mirrors will be more effective that lots of small ones. They would also make it easier to combine the optics.
OTOH, the more the merrier! Maybe someday a much larger array will be built which has individual scopes this large.
eye strain no more (Score:1)
world's biggest pair of binoculars ?
test the chupacamera [vidcard.com]
Re:Why didn't they do this before? (Score:2)
This is general practice in the radio regime, but it is damn hard in the optical. Not only because of the seeing, the distortion introduced by the atmosphere, but also because the phase information in lightwaves at visible wavelengts generally tends to get destroyed when you tamper with it. In an radio-interferometer one tampers a lot with the signal before combining.
The only solution is to build optics of so-called 'interferometric quality' which means that contact surfaces have to be smooth on the scale of a fraction of the wavelenght (!).
Re:Just the start (Score:2)
If the former, then optical VLBI is indeed in trouble. You'd have to quantum-mechanically preserve the photons phase information (without observing it) recombine them later and observe the combination to get useful interference. This might not be impossible -- you essentially need quantum teleportation, which is known to be possible.
If the latter, then you just need a big enough light-bucket and a bright enough source. This would limit the application of optical VLBI, but not rule it out. A 10000km baseline optical interferomter, for instance, would have a 1mm resolution for detail on the surface of the sun, for instance