Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Actual pix of an exoplanet

  1. Nov 14, 2008 #1
    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:

    and in Science Express:

    Actual pictures of an exoplanet! Bravo!

    Here's a short clip from Yahoo with Kalas explaining his discovery:

    Last edited: Nov 14, 2008
  2. jcsd
  3. Nov 17, 2008 #2
    How Finely Can We See?

    Hey, how come everybody isn't jumping in to 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?
  4. Nov 18, 2008 #3

    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.

    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:
    Last edited: Nov 18, 2008
  5. Nov 19, 2008 #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?
  6. Nov 19, 2008 #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:

  7. Nov 19, 2008 #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.
  8. Nov 19, 2008 #7
  9. Nov 19, 2008 #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.
  10. Nov 19, 2008 #9
  11. Nov 19, 2008 #10


    User Avatar
    Science Advisor
    Homework Helper

    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)

    But now look like this:

    (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!
    Last edited: Nov 19, 2008
  12. Nov 20, 2008 #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.
  13. Nov 20, 2008 #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.

    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.
    Last edited: Nov 20, 2008
  14. Nov 20, 2008 #13


    User Avatar
    Science Advisor
    Homework Helper

    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 whats 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.

    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

    Great - hope it works.
  15. Nov 20, 2008 #14
  16. Nov 20, 2008 #15


    User Avatar
    Science Advisor
    Homework Helper

    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.
  17. Nov 20, 2008 #16
    How about this idea?


    The cost seems lower:

    The weight would be lower too:

    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.
  18. Nov 20, 2008 #17


    User Avatar
    Science Advisor
    Homework Helper

    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 accross 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!
  19. Nov 21, 2008 #18
    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.
  20. Nov 21, 2008 #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.
  21. Nov 21, 2008 #20
    This is Planet X, right?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Actual pix of an exoplanet
  1. ExoPlanet Hunting (Replies: 4)

  2. Exoplanet Techniques (Replies: 1)

  3. Exoplanet Maps (Replies: 2)

  4. Name an exoplanet! (Replies: 2)