Follow Slashdot blog updates by subscribing to our blog RSS feed


Forgot your password?

Planet Discovered Using Telephoto Camera Lenses 74

[rvr] writes "The Space Telescope Science Institute (STScI) reports the discovery of an extra-solar planet called XO-1b, which orbits a dim star in Corona Borealis every 4 days. To find it, the brightness of several thousand stars were regularly scanned using two mini-telescopes in Hawaii. This equipment was built using commercial hardware: two digital cameras, attached to telephoto camera lenses on a robotic equatorial mount. A team of amateur astronomers helped with their own equipment to discard or confirm dozens of suspected transits."
This discussion has been archived. No new comments can be posted.

Planet Discovered Using Telephoto Camera Lenses

Comments Filter:
  • Real ingenuity (Score:5, Insightful)

    by bcmm ( 768152 ) on Sunday May 21, 2006 @07:42AM (#15375341)
    That's real ingenuity and intelligence: not throwing money at getting incredible machines to do things for you, but working out what you can do with off-the-shelf stuff and designing a system around it. People have already spent a lot on big telescopes for extrasolar planet hunting.
    • "It's not the size of the hammer, it's how you use it" ... Proven!
    • Re:Real ingenuity (Score:5, Informative)

      by Shigeru ( 598706 ) on Sunday May 21, 2006 @04:56PM (#15377118) Homepage

      I don't mean to diminish the cleverness of those involved in this project at all, but the article summary is a little misleading. While the discovery was made with very small-scale telescopes, the confirmation that this was actually a planet came from two large telescopes, the Harlan J. Smith Telescope (2.7 meter aperture) and the Hobby-Eberly Telescope (9.2 meter effective aperture), as the linked article mentions.

      Finding extrasolar planets by the transit method, where you moniter large fields of stars and look for brightness variations as a planet passes in front of one of your targets and blocks some light, is pretty straight-forward. You tend to only need somewhere between 0.1% and 1% precision in your photometry, which requires some work to achieve, but is by no means prohibitive. So it's a good technique for amateurs to get involved with, especially when you consider that smaller telescopes tend to have larger fields of view, so you can moniter more stars at once. But the main stumbling block transit-searchers have run into is the false positive rate. The biggest surveys have found a huge false-positive rate (90-95%) among the planet candidates. It turns out there are lots of things that can make a star dim at fixed intervals, from grazing binaries to starspots.

      As a result, transit planet candidates are only considered confirmed when there are measurements of a radial-velocity wobble consistent with the orbital period found by the transit. To get the radial velocity precision you need (for the Hot Jupiters transits detect, precision of tens of meters per second is sufficient), it takes a precise, high resolution spectrograph (very expensive), mounted on a large telescope (at least a couple meters).

      I should also point out that transit searches are sensitive mainly to close-in planets. The sensitivity function drops very quickly as the planet moves further out (both because you need a longer sustained campaign, and because the chances of the planet's orbit crossing the star decreases). All the transit detections thus far have been from planets with several-day orbits. While this is interesting science, there's a lot of work to be done with planets in other regimes. The straight-up radial velocity technique gets you planets at seperations between 0 and 5 AU or so (over 150 planets found this way so far), the microlensing method can also detect planets at much larger orbital separations (2 or 3 planets up until now), and direct imaging is ideally suited for large-seperation planets (only the 1 good planet at this point). My point is that you can't cover this whole range of parameter space with small telescopes alone. Radial velocity and direct imaging require large investments in hardware, both in the large telescope itself and the instrumentation (disclaimer: I work on direct imaging, that's why I keep bringing it up). It's also important to note that one of the reasons people find transiting planets so interesting is the possibility of getting spectral information out of the planets. NASA's Spitzer space telescope recently detected the secondary eclipse (the loss of light when the planet is hidden behind the star) of two transiting extrasolar planets. This is pretty exciting science, since you can really compare data to models this way, but it requires some extensive telescope set-ups to get it done.

      So again, this is certainly a great project for getting amateurs involved in the planet-finding game, and I"m very impressed with this result. But don't close down Keck and the VLT and Hubble just yet; there's a lot of work to be done in extrasolar planet research, and much of it requires large telescopes with new (read: expensive) instruments.

    • Re:Real ingenuity (Score:4, Interesting)

      by doubletruncation ( 939847 ) on Sunday May 21, 2006 @05:04PM (#15377142)
      Actually they need to use small telescopes for this kind of project simply because large telescopes won't work. Only 1% of Sun-like stars will have a Jupiter-sized planet orbiting with a period less than ~10 days, and only 10% of these will transit from our point of view. So they need to look at ~1000 sun-like stars to have a chance of getting a single transiting hot jupiter. They're particularly interesting in finding these planets around bright stars since then you can hope to do interesting follow-up like measuring their atmospheres and reflected light. The point is, that to have any chance of finding such a planet around a bright star they need to look at very large fields of view - typically for these kind of surveys a single image will be 5 to 10 degrees on a side (which is 10 to 20 times the diameter of the full moon). It's incredibly difficult to get a very large field of view with a big telescope (for a 6 meter telescope the largest field of view camera that has been built covers half a degree by half a degree), so for this type of project small, cheap, off-the-wall telescopes are the best tools for the job. There are, in fact, a number of similar surveys using small telescopes to look for these things, and a planet (Tres-1) has already been found this way.
  • by Anonymous Coward on Sunday May 21, 2006 @07:43AM (#15375346)
    What the hell is a planet using a telephoto lens for?
    Spying on uranus?
  • Though I could not get to the article text, WOW! If that's what we can do now with such modest optics, I imagine it won't take much more than a decade or two before we're able to detect the signature of life in some extra-solar planet out there.

    (ok, granted this planet was a gas-giant one, but big scopes are not starting to be able find more "earth-like" ones too)

    As the good professor would say, "Good news everyone!"
    • by cnettel ( 836611 ) on Sunday May 21, 2006 @07:53AM (#15375368)
      Note that we don't see the planet. We see that we see less of the light from the star. If the planet would be Earth-like (or a reasonably dense gas giant), we wouldn't get any absorption spectra clues for the chemical composition, as all wavelengths would be absorbed in the "eclipsed" region of the star's disc.
    • Not That Easy (Score:4, Informative)

      by Rob Carr ( 780861 ) on Sunday May 21, 2006 @09:41AM (#15375600) Homepage Journal
      f that's what we can do now with such modest optics, I imagine it won't take much more than a decade or two before we're able to detect the signature of life in some extra-solar planet out there.

      There's an upper limit [] on what can be seen from Earth's surface. Alas, we will need space-based telescopes to find other Earths. I suppose we could find Jupiter-sized planets with lifesigns on them. Given that terrestrial life might have needed a solid surface to evolve on, I'm not sure how likely that is. Then again, it's a big galaxy, and even the weird and unlikely has to happen someplace.

    • Very cool project. I've heard of amateur astrophotographers using fast lenses, but this takes it to a whole new level. The lenses used in this telescope (Canon's 200mm f/1.8 L lens) not only collect an enormous amount of light, but are also among the highest quality lenses ever made.
  • Correct Link (Score:5, Informative)

    by timgoh0 ( 781057 ) on Sunday May 21, 2006 @07:48AM (#15375356)
    The second link in the article appears to be pointing to the wrong place. The correct link should be this []
  • XO-1b (Score:2, Funny)

    by waltew ( 764415 )
    By the amateur astronomers often called Bob.
  • Tight Orbit (Score:5, Interesting)

    by Vlad_the_Inhaler ( 32958 ) on Sunday May 21, 2006 @08:06AM (#15375391) Homepage
    This Jupiter-like planet appears to be a pretty weird case. An orbit lasts 4 days, an object as large as that with an orbit as short as that must be relatively easy to discover. I suppose the thing will not be around much longer anyway - it will impact the sun there.
    • I was just going to post pretty much the same thing. TFA doesnt mention quite how "tight" the orbit is. I would love to know how a planet that large could be orbiting tight & fast. Surely the stars proximity would cause a gas giant that close to be pretty unstable.
    • How do they know this is a planet and not a large sun spot?
      • Re:Tight Orbit (Score:2, Informative)

        by hde226868 ( 906048 )
        First of all, sunspots are more or less static in location on the surface of the star. For typical late type stars the rotation period is similar to that of our Sun, about a month, so you wouldn't see this type of variations on a timescale of 4d (we can measure the rotation speed of stars spectroscopically using standard techniques). Furthermore, even if the star rotates with a 4d period, since sunspots change in shape, each time you see the sunspot pass the surface of the star you'd see a slightly differen
    • Re:Tight Orbit (Score:5, Informative)

      by hde226868 ( 906048 ) on Sunday May 21, 2006 @10:04AM (#15375679) Homepage
      There is no danger in the planet impacting on the star. For this you would have to invoke some mechanism that is able to get rid of the planet's orbital angular momentum, which is very difficult to acheive. So, while the planet is close to its star, it is in no danger of falling in - only very much in the future once the star leaves the main sequence and becomes a red giant. But that's some billion years in the future... (as an aside, a similar misconception is that if a star suddenly turns supernova and becomes a black hole, many people believe that planets surrounding that star would get "sucked in". For the same reason, that's not a problem either). Note that Mercury in our solar system has an 88d orbit, and has happily lived there for 4.5 billion years.

      What is more worrisome is that the planet gets heated up due to its proximity to the star and is evaporated. But again, planets have an awful amount of mass, so this shouldn't be too much of a problem either. For example, there is a 4.4 jupiter masses planet around Tau Bootis, in a 3.3d orbit ( []), but the general estimate for objects of this kind (dubbed "hot jupiters") is that they will survive for billions of years. The reason for this is that the mass loss rate caused by the proximity of the star is still negligible compared to the mass of the planet. Take a look at the article by Ferlet et al., on p. 226 of a recent conference on explanets, the proceedings of which are at s.html [].

      • Your reply assumes a two body stable orbit. This is almost certainly not the case. As soon as there is more than two bodies then we cannot make long term analytic predictions. Even if it is a two body system there are many orbits which appear to be stable for long periods then slowly decay. The orbit of the moon about the Earth is a case where the tidal forces that act between the two closely orbiting bodies allows for the bleeding off of angular momentum and the change in the orbit of the moon and the
        • In most extrasolar planetary systems we have detected so far, the systems are dominated by a small number (1 to a few) of jovians. For all practical purposes these systems can be considered stable on long timescales. For our solar system, which is dominated by a few jovians in the outer solar system, while there are resonance effects between these orbits, which can significantly change the orbital parameters of the inner planets (see, e.g., Laskar, bcode=19 []
          • The orbital radius increases because the earth's rotation velocity is greater than the moon's angular velocity. If the moon orbited the earth quickly (say.. at LEO speeds assuming that were possible...) the transfer of angular momentum would go the other way.

            Also, a jovian IS significant compared to its star. especially as evidenced by the detectable wobble.
            • The orbital radius increases because the earth's rotation velocity is greater than the moon's angular velocity. If the moon orbited the earth quickly (say.. at LEO speeds assuming that were possible...) the transfer of angular momentum would go the other way.

              yes, point taken. To finish this discussion, I have finally found the relevant paper in my files. Piet Hut showed in 1980 that one does reach a stable configuration when more than 3/4 of the total angular momentum of a system is in orbital angular m

    • Actually, if there is any rocky core at all, the planet will most likely be pushed out due to tidal friction. The question is how the planet, and all the otheres, got so close there in the first place.
  • its a fake (Score:1, Funny)

    by Anonymous Coward
    its a sony fake till they build the real planets
  • "[...] the brightness of several thousand stars were regularly scanned using two mini-telescopes [] in Hawaii." a-solar_planet/ []

    Not Found

    umm... this is awkward...
  • by TrixX ( 187353 ) on Sunday May 21, 2006 @12:55PM (#15376303) Homepage Journal

    The transit method allows astronomers to determine a planet's mass and size. Astronomers use this information to deduce the planet's characteristics, such as its density.

    They infer the density from the mass and size! I knew those astronomers were really damn smart!

    (I'm not laughing at the astronomers. I am laughing at the silly article writers that praise the trivial part of the astronomer work instead of the really interesting things that the astronomers do).

    • Of course, they weren't even right. The transit method doesn't tell them anything about mass, they did that using the "wobble" of the star (the way most planets were discovered in the first place), as the very next paragraph explains...
  • by gurutc ( 613652 ) on Sunday May 21, 2006 @02:08PM (#15376557)
    To show my folks how good their middle of the line $300 Fuji 5200 camera was I set it on the roof of my car and did a high resolution .5 second exposure of Jupiter. Then I took the cam inside, loaded the pic on the pc, and zoomed it in to show them the moons of Jupiter and some of the cloud colors on Jupiter itself.
    • Wow, could you share a few more details of how you achieved the shot. I have toyed with night photo's of the moon, but I am not expereinced enought to know how to set it up. I have a Olympus C740. I assume I set manual settings and all, could you give a few clues?
      • Hi, I'd need the camera in front of me, but I'll post what I remember. Set the camera for the highest resolution possible. Turn off all the automatic settings. Turn off any 'digital' zoom features. If your camera has an 'optical' zoom set that as high as it will go. I don't know the technical terms for camera settings, but set focus to infinity and the shutter speed as slow as possible or if you can, set a timed exposure of a full second or more and use the cam's timer to snap the shot although my pare
  • The array method these guys used is the principle for the Very Large Base Array on Mauna Kea. Interesting that they're still working to get the VLBA software working, and these guys in the FA are finding planets.
  • The write-up of their equipment hasn't been published in hack a day [] yet, so it doesn't count!
  • by heroine ( 1220 ) on Sunday May 21, 2006 @02:54PM (#15376716) Homepage
    Those 200mm lenses are truly underappreciated masterpieces. They are so over engineered, they can exceed telescopes for most wide field astronomy. Unlike most telescopes of equivalent quality, the EF 200mm is portable.

    As time progresses and more people can afford digital SLR's, the EF 200mm F2.8 L II is going to make a lot of astonomical discoveries.

  • by Flying pig ( 925874 ) on Sunday May 21, 2006 @04:10PM (#15376949)
    Sorry to be a lens Nazi, but these are hardly telephoto lenses. "Telephoto" does not just mean "Long focal length", it has a specific meaning. A telephoto lens has its optical centre OUTSIDE the front element; it is how it is possible to produce (say) a 600mm lens that is only 300-400mm long. These are 200mm f/1.8 and I suspect the optical centre of being inside of the front element. 200mm wide aperture lenses (which are hardly routine amateur stuff) usually work with matched telephoto adaptors at which point they DO usually become telephoto lenses in combination.

    Telephotos are always an optical tradeoff where the compact dimensions are at the expense of various kinds of optical goodness. Reverse telephotos, used to give enough room in the shutter box between the film and the rear element of, say, a 21mm lens, are a different matter; they can be well designed because the greater distance to the rear element means the maximum angle of the exit rays is lower. Leitz were always able to get the best optical quality for their M series rangefinders, though, because the absence of the mirror box give fewer constraints in rear element placement.

    Interestingly, if you are a lens geek, telephotos were originally developed because early news photographer cameras did not have enough extension on their baseboard bellows to focus long lenses. bellows to

  • Are they using two lenses to double the light captured, or is there some other reason?

    Did they use refractors vs. an off the shelf 8" or 10" SCT for higher contrast?

    It would be nice to know more about the design and trade-offs of the entire camera.

    • You are looking for a slight dimming. The atmosphere of the Earth can provide slight dimming. Two cameras looking through different bits to of the Earth's atmosphere can provide extra confidence that the dimming you detect is not here at home.
  • by XO ( 250276 )
    I'm so goddamn special, they named a whole PLANET after me!

"I shall expect a chemical cure for psychopathic behavior by 10 A.M. tomorrow, or I'll have your guts for spaghetti." -- a comic panel by Cotham