What are the benefits of using interferometry for exoplanet hunting?

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In summary, Astronomy magazine has a story that a team of astronomers have actually taken IR pictures of an exoplanet system around HR 8799, about 130 light years away. There are three planets, all larger than Jupiter, visible as three specks in the pictures. In addition, a team from the University of California has Hubble pictures in visible light of a triple Jupiter mass exoplanet orbiting Formalhaut, which is 25 ly away. Both discoveries are firsts for the exoplanet hunt.
  • #1
Arch2008
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The German magazine Bild has a story that a team of astronomers have actually taken IR pictures of an exoplanet system around HR 8799, about 130 light years away. There are three planets, all larger than Jupiter, visible as three specks in the pictures. In addition, a team from the University of California has Hubble pictures in visible light of a triple Jupiter mass exoplanet orbiting Formalhaut, which is 25 ly away. Both discoveries are firsts for the exoplanet hunt.

Here's a link to a story in Astronomy about this:
http://www.astronomy.com/asy/default.aspx?c=a&id=7599

and in Science Express:
http://www.sciencemag.org/sciencexpress/ [Broken]

Actual pictures of an exoplanet! Bravo!

Here's a short clip from Yahoo with Kalas explaining his discovery:
http://news.yahoo.com/s/ap/sci_new_planets [Broken]

______________
 
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  • #2
How Finely Can We See?

Hey, how come everybody isn't jumping into discuss this momentous discovery?? Is the main discussion thread on this somewhere else?

I was thrilled when this news came out, and have been devouring every piece of news I can find on it.

Anyway, I came back here to ask -is there any limit on how finely we can resolve the details of a distant planet? I understand our own atmosphere causes some problems, but there have been advances in adaptive optics, and there are also planned space-based telescopes (James Webb Space Telescope, etc). But so then is there any inherent physics-based limit on how finely we can make out details? (ie. like a 'barrier law')
For instance, might we be able to see continents on some distant Earth-like planet one day?
Or is that absolutely unreasonable?
 
  • #3
http://planetquest.jpl.nasa.gov/missions/simMission.cfm [Broken]

This says that imaging details on Earth-like exoplanets is possible with astronomical interferometry. (It’s also a great site for keeping track of exo’s) This is the process of taking images from two or more telescopes and combining them into one image.
http://en.wikipedia.org/wiki/Interferometry

I suppose that quantum physics would limit the fraction of a wave that could be reintegrated and computing power would play a role as well. It is possible to use telescopes with considerable separation to resolve combined images into one. I read that images from one Earth-bound telescope taken over several days, and thus from different locations in space, have also been used to create an enhanced image as well. I heard a claim once that eventually city lights might be visible in an exo’s image.

P.S. I found this paper which offers a more detailed explanation of optical interferometry:
http://www.submm.caltech.edu/papers/pdf/2002-05-OSA-Zmuidzinas.pdf
 
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  • #4
Wow, I personally would love to see detailed images of another Earth in my lifetime. Just think of what a thrill that would be!

So to what extent does interferometry benefit from aperture size? Or does it mainly benefit from the separation distance between the multiple viewing apertures?
Based on the prospective state of our technology in the near future, what would be the best combination of aperture size and separation distance possible?
 
  • #5
And so how high do such interferometry telescopes have to be, in order to function properly? Can they only function in pure vacuum, or could they work if you were above, most of the atmosphere, at say, 0.1 atm?

What if you had one of these AWACS-style aircraft flying at high altitude, but instead of carrying a large radar disc, it was instead carrying some kind of large parabolic reflector dish?

Or what if you had a huge aerostat-balloon the size of the Hindenberg, but having a toroidal/innertube shape. In its donut hole you could place a large parabolic reflector dish, to scan the heavens with. You could make the balloon skin out of graphene, which has high strength-to-weight and is impermeable to gas leakage, even with respect to gases like hydrogen. It could then float high up for very long periods of time, at an altitude of maybe 45km. This could keep it above atmospheric effects like wind, turbulence, optical distortion, etc. The balloon could have a photovoltaic coating to harvest solar energy to power its equipment, and even ion-wind thrusters for some maneuvering capability.

Such a high-altitude balloon could be more easily recalled for maintenance and upgrades, and could serve as a robust, versatile and reusable platform for deploying a variety of science packages, such as "space telescopes", etc.

Why couldn't such an idea work?

TIME Magazine, 1957:

http://www.time.com/time/magazine/article/0,9171,810000,00.html
 
  • #6
Many of your questions are unknowns that NASA scientists are attempting to answer. The paper showed statistical comparisons of linking up to ten telescopes. The telescope was invented about 400 years ago, but we are still learning how to use them. Here’s a glimpse of what is coming soon.
http://www.astronomy.com/asy/default.aspx?c=a&id=3049
 
  • #8
Yes, as one of the links explained, interferometry comes from the words interfere and measure. When two light waves are combined they either compliment each other so that a stronger image results or the “crest” of one wave and the “trough” of the other cancel each other in the so-called nulling effect. This effect allows software to “turn off” the light of a star so that the faint reflected light of an orbiting exoplanet can be imaged. Our present telescopes are like flint tools compared to what we are planning to do.
 
  • #9
Have you heard of this French astronomer, Antoine Labeyrie?
He has a proposal for a 'hypertelescope' -- an Exo-Earth Imager:

http://www.space.com/scienceastronomy/astronomy/exoearthimager.html [Broken]

Read this too:

http://www.astronomycafe.net/anthol/remote.html [Broken]

Wow, if this kind of stuff is achieved, then it'll be Astronomy 2.0 for sure!
 
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  • #10
Perhaps I can clear up a few misunderstandings.

The Hubble image is about the same resolution as you can achieve with ground based telescopes and adaptive optics. The main advantage of Hubble for this sort of image is that there is no atmosphere to scatter the light from the star over the light from the planet. THis is about the limit of what you can see with regular telescopes - it just happens to be a particularly large and bright planet around a not so bright star. The next gen space telescoep will do a bit better, not only is it larger (and so more sensitive and higher resolution) but it's infrared performance is better - the difference in brightness between a star and a planet is less in the IR.

To do much better than a one pixel dot you need an interferometer - which combines the light from many small telescopes to give you an image with the same resolution as a single large telescope. It's also possible to take out most of the atmospheric effects with these sort of instruments.

They started out looking like this ( which is still 20x better resolution than Hubble)
http://www.mrao.cam.ac.uk/telescopes/coast/coast04.jpg [Broken]

But now look like this:
http://www.onera.fr/conferences-en/naos/images/photo-vlt.jpg [Broken]

(guess which was built by the Brits and which by the Germans!)

Unfortunately they are not very sensitive and so you need a bright planet. Putting them in space has a small advantage that you can look at the same object for a long time - but space telescopes are smaller (each of those telescope mirrors is 10x larger than Hubble).

Interferometers don't directly cancel out the light of the star, there is a device called a nulling interferometer which can do this - but no one has built one suitable for astronomy. This is the best attempt so far - it's two 8m mirrors making up a pair of binoculars!
http://www.mpia.de/Public/LBT/bilder/lbt.jpg [Broken]
 
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  • #11
So interferometry can be done using ground-based telescopes then.

So why not just set these things up on the ground, at places like Mauna Kea? How much advantage does space really offer?

I'm still wondering why giant balloons floating at the top of the atmosphere wouldn't be feasible as platforms. If bulk-manufacturing of graphene really takes off, then I'm sure balloons will become the ideal platforms in the future.

Btw, I read about some project called PRIMA that is indeed implementing a nulling interferometer.
 
  • #12
Huge present day telescopes are a true marvel of technology equal to an earlier Wonder of the World. Light from a distant star shines onto a mirror that focuses the light to increase the final image received. Thus, the bigger the mirror that you have the better the image you receive. However, at some point the mirror is so large that it will crack from its own weight. So large individual mirrors the shape of honeycombs are combined to create huge segmented mirrors (as with the planned Hundred Meter Telescope). Each individual mirror’s surface can further be shaped by sensors to “adapt” it to weather and atmospheric conditions, so that the final image is even sharper. Unfortunately, the whole apparatus weighs many tons and is very sensitive, so putting it into orbit or on a balloon becomes prohibitive. Huge Earth based telescopes and relatively smaller orbital telescopes are the best we can do at present. Combining telescopes using interferometry is also constrained by budgets. When an individual telescope project costs more than a billion US dollars, then funding several to be linked together (as the telescopes at Cerro Paranal, Chile) is very expensive.
http://www.astronomy.com/asy/default.aspx?c=a&id=1176
http://www.astronomy.com/asy/default.aspx?c=a&id=6530


There are plans to fill a crater on the dark side of the Moon (no atmosphere or interfering city light) with many telescopes linked together, but so far it is just a plan.
 
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  • #13
So why not just set these things up on the ground, at places like Mauna Kea? How much advantage does space really offer?
In space you don't need adaptive optics to correct the atmosphere and you can point at a single object for a long time.
You also don't need what's called a delay line. As a start rises and sets on a ground based system all 4 scopes have to track it, but the distance from the star to each scope is constantly changing - you need complicated optics to constantly adjust for this difference.
With a space based system you just point it at a star and wait - of course pointing a space telescope in the same direction to a fraction of wavelength of light is also tricky.

I'm still wondering why giant balloons floating at the top of the atmosphere wouldn't be feasible as platforms.
At Mauna Kea or Chile you are already above most of the weather and water vapour.
Those telescopes are about the size of 10story buildings, putting them on a balloon would be tricky.
You can put smaller telescopes on aircraft (sofia is a 747) this is normally done for infrared where you need to get as high as possible since it is absorbed by the atmosphere.
Before satelites, X-ray telescopes went on ballons - but they are small and don't have to be pointed acurately

Btw, I read about some project called PRIMA that is indeed implementing a nulling interferometer.
Great - hope it works.
 
  • #15
The NASA terrestrial planet finder is developing one - the keck run is a test of the prototype.
The problem used to be that they can only be used at very narrow bandwidths and had poor efficency so you lost a lot of light. I don't know if the TPF or VLT have solved this.
 
  • #16
How about this idea?

http://science.nasa.gov/headlines/y2008/09oct_liquidmirror.htm [Broken]

"It's so simple," says Ermanno F. Borra, physics professor at the Optics Laboratory of Laval University in Quebec, Canada. "Isaac Newton knew that any liquid, if put into a shallow container and set spinning, naturally assumes a parabolic shape—the same shape needed by a telescope mirror to bring starlight to a focus. This could be the key to making a giant lunar observatory."

The cost seems lower:

The biggest liquid-mirror telescope on Earth, the Large Zenith Telescope operated by the University of British Columbia in Canada, is 6 meters across—a diameter 20 percent larger than the famous 200-inch mirror of the Hale telescope at Palomar Observatory in California. Yet when completed in 2005, the Canadian Palomar-class liquid-mirror telescope cost less than $1 million to build—only a few percent the cost of a solid-mirror telescope of the same diameter--and, for that matter, only a sixth of Palomar's original cost in 1948.

The weight would be lower too:

The fact that a liquid-mirror telescope always looks straight up vastly simplifies its construction and reduces mass by eliminating heavy mounts, gearing, and pointing-control systems needed for a steerable telescope. "All you'd need is the liquid-mirror container, which might be an umbrella-like device that self-deploys, plus a nearly frictionless superconducting bearing and its drive motor," Borra says. Worden estimates that all the materials for an entire lunar telescope 20 meters across would be "only a few tons, which could be boosted to the Moon in a single Ares 5 mission in the 2020s." Future telescopes might have mirrors as large as 100 meters in diameter—larger than a football field.


I'm sure something like this could be mounted on a giant innertube-shaped balloon. The only difference between their moon mission and what I'm saying, is that a balloon is cheaper than a moonshot, and it would probably allow you a larger payload. Also, you're a lot less constrained on the size, the design and the geometry of your telescope apparatus, as compared to what would be required for a lunar deployment.

If some breakdown occurred later on, you could recall the balloon back to the ground and have things fixed. You'd have the advantage of being able to assemble and test everything on the ground, before the balloon was even launched.

If the balloon had a photovoltaic surface to gather power, it might be able to use it to power electromagnets to rotate the liquid mirror like a giant flywheel.

Once graphene becomes available as part of bulk composite materials, I'm sure something like this could become feasible.
 
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  • #17
sanman said:
I'm sure something like this could be mounted on a giant innertube-shaped balloon.
There is no reason to put an optical telescope on the moon rather than in orbit.
There is a french astronomer who keep scoming up with plans for things like reflective spider legged robots that would be launched onto the moon, they would then find each other and meetup to make a giant telescope!

It's rather tricky to rotate something at a constant rate while it is floating in the air - you would have to use little jet engines! The problem with a liquid mirror is that it can only look straight up and so the stars move constantly across the image. This is fine for quick pictures for surveys - but not much use if you want to stare at the same object for days!

If the balloon had a photovoltaic surface to gather power, it might be able to use it to power electromagnets to rotate the liquid mirror like a giant flywheel.
You normally want a telescope mirror to be reflective - solar panels have to absorb light!
 
  • #18
mgb_phys said:
There is no reason to put an optical telescope on the moon rather than in orbit.
There is a french astronomer who keep scoming up with plans for things like reflective spider legged robots that would be launched onto the moon, they would then find each other and meetup to make a giant telescope!

It's rather tricky to rotate something at a constant rate while it is floating in the air - you would have to use little jet engines! The problem with a liquid mirror is that it can only look straight up and so the stars move constantly across the image. This is fine for quick pictures for surveys - but not much use if you want to stare at the same object for days!


You normally want a telescope mirror to be reflective - solar panels have to absorb light!

The innertube-balloon would be absorptive for photovoltaic power generation, with the added benefit of reducing glare or light pollution. The liquid mirror flywheel apparatus would be sitting on or inside the donut hole.

Secondary mirrors would be used to redirect light onto the main reflector, as is the case with other immobile dish telescopes, including Arecibo.

As for maneuvering, you can use electrostatics for propulsion, using ion-wind thrusters.
Electrostatics is used to accelerate ionized air, to generate thrust.
 
  • #19
Great link! I must admit, I had never heard of such a telescope. After four centuries, we are still developing this little carnival toy!
From what I read thus far, the Liquid Mirror Telescope (LMT) seems limited to large sky surveys and not planet hunting. At least it is not listed as one of the possible uses. However, a high resolution survey wouldn’t hurt a planet search, I suppose. As before, there doesn’t seem to be an upward limit on the resolution. What might a 100+ meter LMT reveal to us?
Since the LMT must remain upright to operate, because the mirror is slowly spinning liquid, I don’t know how well that would work on a balloon in flight. Just a thought.
 
  • #20
This is Planet X, right?
 
  • #21
http://en.wikipedia.org/wiki/Planets_beyond_Neptune

Not quite, planet X was to be the tenth planet (X stood for unknown and was also the Roman numeral for 10) in our own solar system, (back when Pluto was the ninth planet). Now it commonly means the next as yet unknown trans-Neptunian planet in our solar system. Exoplanets are planets that orbit other stars.
 
  • #22
Lovely! I can't wait for more pictures of exoplanets to be taken. Does anyone know if we can expect more of these to be taken of other planets in the near future?
 
  • #23
sanman said:
So interferometry can be done using ground-based telescopes then.

So why not just set these things up on the ground, at places like Mauna Kea? How much advantage does space really offer?

I'm still wondering why giant balloons floating at the top of the atmosphere wouldn't be feasible as platforms. If bulk-manufacturing of graphene really takes off, then I'm sure balloons will become the ideal platforms in the future.

Btw, I read about some project called PRIMA that is indeed implementing a nulling interferometer.

The distance between the 2 scopes has to be tracked to less than the wavelength of the light you are trying to combine.
 

1. What is an exoplanet?

An exoplanet, short for extrasolar planet, is a planet that orbits a star outside of our own solar system. These planets can vary in size, composition, and distance from their host star.

2. How do scientists take actual pictures of exoplanets?

In order to take an actual picture of an exoplanet, scientists use a variety of techniques such as direct imaging, where they take a picture of the exoplanet itself, or indirect methods such as measuring the effects of the exoplanet on its host star.

3. What are some challenges in capturing images of exoplanets?

One major challenge in capturing images of exoplanets is the vast distance between us and these planets. They are often very small and far away from their host star, making them difficult to detect and capture with current technology.

4. How do scientists confirm that a picture is actually of an exoplanet?

Scientists use a variety of methods to confirm that a picture is actually of an exoplanet. This can include analyzing the spectrum of light from the planet, determining its mass and orbital path, and ruling out any other possible explanations for the image.

5. What can we learn from images of exoplanets?

Images of exoplanets can give us valuable information about the composition, atmosphere, and potential habitability of these planets. They can also help us better understand the formation and evolution of planetary systems outside of our own.

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