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Exoplanets Ahoy!

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  • Tom Curtis
    Steve Jones is arguing that the current inability to find Earth like planets proves that they are rare or non-existant outside our solar system. Pi has
    Message 1 of 1 , Sep 1, 2004
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      Steve Jones is arguing that the current inability to find Earth like planets proves that they are rare or non-existant outside our solar system.  Pi has pointed out to him how shonky his statistical argument is, to no avail - but it is worse than Pi indicates.
       
      NASA's recent announcement of the discovery of two new exoplanets gives a measure of the sensitivity of current techniques.  These planets are 10 to 20 times the mass of the Earth.  These planets are detected by measuring the changes of motion they cause in their respective suns.  Given that, and given that acceleration is linearly correlated with mass, current techniques would have to improve their sensitivity by a factor of 10 in order to detect an earth mass planet in the same orbit.
       
      It is worse than that.  These planets are extremely close to their suns - in fact less than a twentieth of the Earth's distance from Sol.  Acceleration due to gravitational attraction in negatively correlated with the square of distance.  Thus current techniques must be improved in accurracy by a factor of 4,000 before they can reasonably be expected to detect Earth sized planets in Earth type orbits.
       
      But because we have not detected objects 4000 times more difficult to detect than those we are currently finding, Jones concludes that those objects are simply not out there to be detected.  His reasoning is on a par with the Galilleian sceptics who concluded that because the Gallilleian moons of Jupiter could not be seen with the naked eye, they did not exist.
       
      What gets me is that on Jones' list are a "science writer" and a member of the NAS.  You would think they would be able to pick up, and advise Jones of the woe full inadequacy of his reasoning - being "truth seekers" and all.  But no!  Not a peep is heard.  Proving once again that their is no limit to the nonsence that a creationist "truth seeker" will let pass, just so long as it is rhetorically usefull to their cause.
       
       
      There are ways of measuring the liklihood of an earth like solar system given the current data.  One method assumes (probably correctly - see second link above) that there are two methods of forming planets.  We can then measure the hot-jupiter solar systems as a proportion of all systems searched.  Earth-like systems will then be a subset of those which are not hot-jupiter systems.  Alternatively, we can assume  that earth like systems are formed by the same process as hot-jupiter systems.  Assuming this, our system lies 2.3 standard deviations from mean of all systems discovered for orbital distance and eccentricity of Jupiter.  This suggests that around 0.3% of planetary systems are earth-like.  Won't that be a blow to the naturalists.  Only three of every thousand suns having earth-like solar systems.  Some how I don't think creationists would find comfort from these figures if they actually tried to understand them.
       
      Tom Curtis
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