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Thread: Extrasolar planets

  1. #1 Extrasolar planets 
    Forum Freshman U-BoaT's Avatar
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    ok i know there are loads of these! they are being found as we speak! and i know that we find them by seeing their shilouette passing in front of the stars they are orbiting! but how far can our knowledge go about these planets? how can we know their composite materials, atmosphere composition, if they have water; etc...can we know this already? and how can our tech evolve to the better understanding of this planets?


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    Forum Ph.D. Nevyn's Avatar
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    We can use a spectrometre to find out what a planet is made of (i think)


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    Forum Freshman U-BoaT's Avatar
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    yes but a spectrometre reads the radiation emitting from the planet to the space i believe, based on the colors radiating from it...but doesn't that only give us a small idea of what composites exist?
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    a lot are thought to be because of erratic solar movements. the current figure i recall is about 260, but many feel any solar unit should have planets or left over debris from formations.

    time exposure is a problem when trying to see things that only reflect light. the same is true even in open space where much mass should exist.
    what planets are made of should be similar to there sun which i understand is some what understood.
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    Forum Ph.D. Nevyn's Avatar
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    A spectometre takes the light from an object and reads it's composition, they use it in industries such as metal work to read the products formed in th process of making alloys
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  7. #6 guys..... 
    Forum Professor leohopkins's Avatar
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    Guys.......forgive me if I am incorrect, but as far as im aware spectrometre's can only be used on objects which emit radiation. erm...Like stars.

    Planets would warp the radiation around the planet due to gravity otherwise the planet would reflect or absorb the radiation.

    I dont think spectrometre's would work on planets.
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  8. #7  
    Forum Ph.D. Nevyn's Avatar
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    maybe it does and mayby it doesn't but it can be used to measure the compositions of stars
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    Forum Freshman U-BoaT's Avatar
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    but doesn't the planet, by orbiting the star, leaves a trace, or a wake, of materials that can be analyzed? i don't think that the spectometer would work in here...as it only read the light coming from the star
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  10. #9  
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    Quote Originally Posted by U-BoaT
    but doesn't the planet, by orbiting the star, leaves a trace, or a wake, of materials that can be analyzed? i don't think that the spectometer would work in here...as it only read the light coming from the star
    Venus and mars do - it's their upper atmospher getting stripped away.
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  11. #10  
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    Since spectroscopy is mentioned so much here, I figured I'd talk a little about it...

    There are 3 types of spectra (this is Kirchhoff's laws)

    Law 1: continuous spectrum - a dense object (solid, liquid, or dense gas) excited to emit light will radiate at all wavelengths producing a continuous spectrum. The dense object is referred to as a black body.

    Law 2: emission spectrum - a low-density gas excited to emit light will do so at wavelengths specific to the elements in the gas.

    Law 3: absorption spectrum - light observed from a black body passing through a low-density gas will have wavelengths specific to the elements in the gas "removed" or "absorbed out" from the continuous spectra resulting in an absorption spectrum.

    Note that the difference between an emission and absorption spectrum is from where you are observing the gas. If the blackbody is directly behind the gas you get absorption, if the black body isn't behind it, you get emission. Also note that typically an emission spectrum is much less intense than an absorption spectrum (in astronomy) if taken with the same time interval (I'll leave the reader to figure answer why this is).


    So...
    how does this relate to the planet discussion? A planet is dense, so it can only give off a continuous spectrum - it radiates as a black body. Since the spectrum is continuous, we can't identify the elements it's made of (though perhaps we could identify elements in its atmosphere as that would produce an absorption spectrum.



    Questions you may have after reading that;

    If a black body radiates at all wavelengths, and the sun is a black body, then how do we know what the sun is made of?
    --- We observe an absorption spectrum from the photosphere, an emission spectrum from the chromosphere, and, believe it or not, a continuous spectra with emission lines superimposed on it from the corona. From these we can determine the chemical composition and even the abundances.

    So... can we then detect an extrasolar planet by its black body radiation?
    --- It would be hard. The peak wavelength for a black body is given by Wien's law, and for a modest planet, it would most likely be in the infrared. That is not the problem though... the luminosity of a black body (given by the Stefan-Boltzmann law) goes like the temperature (in Kelvins) to the fourth power (T<sup>4</sup>). For a low temperature planet (compared to its parent star), the radiation from it would be drowned out by its star. Luminosity also goes like the surface area of the black body - since a planet is small, it would radiate much less than its parent star further hindering its detection via observing its radiation.

    If we don't see an element in a spectrum, can we conclude that it's not present?
    --- No. If the black body is too hot, it will ionize those atoms, and if too cool, it won't excite those atoms. Either way, those atoms may be present but would not show up in the spectra. On the other hand, if we see the wavelengths which correspond to a certain atom/ion, then that atom/ion must be present since each atom/ion has its own distinct wavelengths (energy levels).

    Will any dense object radiate as a black body - such as an ice cube?
    --- Yes. Any dense object above absolute zero. Humans are about at 310 Kelvins (K). We radiate mostly in the infrared (actually, when the doctor sticks that thing in your ear to measure your temperature, really the doctor is measuring the wavelength coming from within your ear and that "thing" converts that wavelength to a temperature via Wien's law). An ice cube, which is roughly 273 K, also radiates mostly in the infrared. Our sun with a surface temperature of roughly 5,800 K peaks in the visible (probably why we evolved to see the visible region combined with the fact that our atmosphere filters out many of the other wavelengths).

    You said that a black body radiates at all wavelengths, and that an ice cube radiates like a black body, so does an ice cube give off x-rays?
    --- For the most part, the answer is no. Surely a black body at a high enough temperature radiates x-rays and all other wavelengths, but the ice cube at 273 K (compared to 5,800 K of our sun) is not quite hot enough. But... it is not out of the realm of possibility. However, there would be so little radiation of short wavelength that you could safely consider it to be zero.

    If there are any questions about this, fire away, else continue with the planet discussion.

    Cheers,
    william
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  12. #11  
    Forum Freshman U-BoaT's Avatar
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    william thanks

    your post has been quite elucidative about all my questions! you even aproach further doubts i was hopping to post

    thanks
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  13. #12 Re: Extrasolar planets 
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    Quote Originally Posted by U-BoaT
    ok i know there are loads of these! they are being found as we speak! and i know that we find them by seeing their shilouette passing in front of the stars they are orbiting! but how far can our knowledge go about these planets? how can we know their composite materials, atmosphere composition, if they have water; etc...can we know this already? and how can our tech evolve to the better understanding of this planets?
    if your still around, just ran across something that may interest you. at "space.com" on 2/7/07, they previewed an upcoming mission. The Kepler, will launch in November of 08, with the sole purpose to watch over 100,000 stars looking for dimness from them, which will indicate planets and so on. the information in this article and additional readings will be interesting to you....
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  14. #13  
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    thanks jackson33...actually i've been watching some news about the kepler! it's specifications are amazing! the hubble is a wonderful machine, but the kepler, as it seams, will be our eye in space
    "We must believe in luck. For how else can we explain the success of those we don't like?"
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