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Detection of non-transiting exoplanets

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The new Kepler telescope is designed to detect planets that transit in front of their stars, however this only works for about .5% of stars that are on the correct plane for viewing. For detecting planets that are on different planes, perhaps background stars could be used? First, remove the target star from the data, then watch the background stars for recurring light-dips, indicating a planet. This will probably need a whole new telescope, I'm not sure Kepler could handle it.
simonj, Jun 05 2009

"Methods of detecting extrasolar planets" at WIkipedia.org http://en.wikipedia..._extrasolar_planets
While difficult, direct imaging isn't impossible. (And apparently background stars can be used to detect foreground planets - via lensing) [phoenix, Jun 05 2009]

How to identify the regular pattern of a norbit http://en.wikipedia.org/wiki/Norbit
Sorry. [phoenix, Jun 05 2009]

Kepler 22b http://www.thestar....ience-world-excited
[simonj, Dec 07 2011]

quantum imaging Quantum_20linked_20...scribes_20cognition
[beanangel, Dec 09 2011]


       I'm not sure and I'm just guessing, but I don't think it would work. (a) The planet's own sun offers a far, far bigger target disc than distant stars, so the chances of the planet occulting another star might be small (?) (b) I don't think you could digitally process out the overwhelming brightness of the planet's own sun and still see very small changes in brightness of "adjacent" stars. This, after all, is why it is so hard to see the planets directly (ie, you can't subtract out the star's own light without losing the planet). (c) all stars move relative to one another, and also a planet's orbit will precess; I would imagine this means that the planet will not occlude the same 'background star' repeatedly, and it will be very hard to identify the regular pattern of a norbit.
MaxwellBuchanan, Jun 05 2009

       You could mask out the target star ie. have a physical barrier in the centre of the lens.
simonj, Dec 07 2011

       A] //chances of the planet occulting another star might be small// If your seeing distance is large enough, the sky is very, very crowded. If the universe were infinite the night sky would be bright. Of course, it's not, so there are dark spaces. But your point A might also be used to argue that there was no hope of ever seeing gravitational lensing. And yet that's been done. Intuition's not reliable here: t's a quantitative, empirical question, that an astronomer could answer. However, the fact that this isn't done already suggests that some astronomer has.   

       B] //digitally process out the overwhelming brightness of the planet's own sun and still see very small changes in brightness of "adjacent" stars.// You don't need to. You just have to detect a very small AC oscillation superimposed on a much larger DC baseline. Which is exactly the sort of signal processing used to detect occulting planets. Except, in this case, it's (in one respect) easier, because the spectrum of the AC component is different* from that of the DC component.   

       *Even if the spectral lines are identical, the red shift'll be different.   

       C] Who says the exoplanet needs to occult the *same* backround star on every orbit? Complicates the signal processing, some, but that'd be the least of ones worries -- points A & B are stronger.
mouseposture, Dec 07 2011

       [simonj]: I don't think that's the problem - you could do the same thing by electronically "masking" the relevant pixels on the image. (Actually a physical mask might be worse, because light will diffract around its edges.)   

       I suspect that there are several reasons why you can't "subtract" the main star sufficiently well, though I don't know which ones are most important:   

       A) light scattering. Interstellar dust and stuff must scatter some light, so a tiny percentage of the main star's light would be superimposed on the surrounding field of view. This might be especially true for stars with planets, since they probably have lots of dust and crap orbiting around them.   

       B) gravitational bending of light. Spacetime is all rippley, which will have a similar effect to scattering, in that it will tend to confuse the light of the main star with that of nearby (in line-of- sight) stars.   

       C) Angular resolution. The angle between the exoplanet (and the eclipsed background stars) and the main star is going to be incredibly tiny. The necessary angular resolution to discriminate the exoplanet (or the eclipsed stars) from the main star would require an FET.   

       So, overall, I think the problem is like trying to detect a moth by watching it "eclipse" the lights from a few glow-worms. The moth and the glow- worms are all a few inches away from an arc-light, and you're looking at the whole scene from fifty miles away, through a sandstorm and heat- shimmer.
MaxwellBuchanan, Dec 07 2011

       Stars come in different types, right? What if your detector was not for visible light, but for some other kind of radiation that the target start is poor in, but the background stars are rich in?
simonj, Dec 07 2011

       That would help. It should also be a doddle to detect exoplanets orbiting black holes, or mauve dwarfs.
MaxwellBuchanan, Dec 07 2011

       This is the part of planet-hunting that has always concerned me - we are only looking for / can only see the tiny fraction of planets that have nicely aligned orbits.
It makes you think; there have been about 2000 exoplanets found now, and if [simonj]s 0.5% is correct (sounds about right...), there are a shiteload more out there!
Finding the rest is where the fun science begins!
neutrinos_shadow, Dec 07 2011

       This might work for visual doubles i think but i haven't done the arithmetic yet.   

       Edit: Now i will. I'm not aware of any particularly close doubles, so i'm going to imagine the Alpha Centauri system is a optical double as well as a ternary system. If a planet was situated at three hundred AU and occulted or transited the hypothetical star at maximum elongation, it would be separated by almost four minutes of arc. So, looking at a real optical double, Secunda Giedi is thirty-three parsecs away and its optical double, Algedi Prime, over two hundred parsecs away. They are separated by six minutes of arc. To transit Algedi Prime, a planet would therefore have to be almost two thousand AU from Secunda Giedi. If its orbit at that distance had a semimajor axis of that size and orbited , that would give it a sidereal period of thirty-three millenia. A planet twice the diameter of Jupiter at that distance would be travelling at six and a half kph. Algedi Prime is a yellow supergiant with a diameter forty times the Sun's, but is six hundred and ninety light years away, so its apparent diameter is four hundred thousandths of an arcsecond. At a sixth of that distance, i.e. the hypothetical planet's distance, the angular diameter of this planet would be about a seventh of the more distant star's, and would take nearly four decades to cross the disc at average speed. This may be very wrong incidentally, i've lost concentration. However, since it would be foreshortened at maximum elongation, it would take a heck of a lot longer than that.   

       So assuming that a planet could orbit that far out from a star, and there's no information on that so far as i know, and with these very shaky calculations, rather surprisingly, it probably does very occasionally happen. However, the orbital plane of the planet would have to be oriented correctly, just as it would with a transit of its own star.   

       I think that if we were able to view every known star in the sky from every other known star system, the chances are that now and again this would happen, but i have no idea how probable it is that it happens in our own sky or if there's been enough accurate observation for this to have been observed. It'd be better from orbit of course. The best chance would be from an optical double whose more distant component was very large, the separation was very close and the planet was very distant from its primary and very large.
nineteenthly, Dec 08 2011

       just being an idiot, perhaps a post heliopause Big Laser could create quantum linked photons that had stabilities of multilightyear duration. Then when the special IR spectroscopy frequency photons reached something thrilling like water, it would create a particular quantum event at the earth system optical observer. The idiot part is mostly, is it really possible to keep huge quantities of quantum linked photons stable while the explorer photons travel light years to be absorbed. One reply is that linked photons lasting minutes are already 10^8 or more longer lived than atomic transitions thus 10^14 might work long enough to detect custom absorbants light years away
beanangel, Dec 09 2011


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