Planet occurrence frequency

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doubletruncation

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<p>A really interesting paper on the statistical results from the Keck radial velocity planet search appeared on the ArXiv tonight - see http://arxiv.org/abs/0803.3357</p><p>This paper presents a statisical analysis of the planets that have been found to date by the survey to determine the distribution of planets as a function of planet mass, orbital period, and stellar mass. While this sort of thing has been done before, this is the largest homogenous sample of stars/planets that has been used to date - which makes it particularly interesting. The results are as follows: out of 585 stars that they surveyed, they found 48 planets. They conclude that <em>they have found every planet around these stars</em> with an orbital period less than 2000 days, a velocity amplitude greater than 20 m/s, and an eccentricity less than 0.6. After accounting for their incompleteness, they find that for the 475 F, G and K-type stars in their survey, 10% have planets with masses between 0.3-10 jupiter masses and orbital periods between 2 and 2000 days. They find that the frequency of planets per unit logarithm in planet mass decreases as M^-0.31 while the number per unit logarithm in period increases as P^0.26 - so smaller gas giant planets are more common than larger ones, and longer period gas giant planets are more common than short period ones. Extrapolating this result, they find that 17-20% of FGK stars have a gas giant planet within 20 AU. It's interesting that while gas giants are not unusual, apparently most stars don't have any (as has been known for a number of years now, the frequency does appear to increase dramatically with the chemical composition of the star, so gas giant planets are quite common around stars that are richer than the sun in heavy elements). </p><p>I think this paper is quite interesting because it really shows that we're now learning a lot about the population of planets in the galaxy, and have moved well beyond the stage where merely finding new planets is the main motivation. Of course on the fringes (small planets, transiting planets) you still hear about each individual planet that is discovered, but we're probably to the point where individual transiting jupiter-sized planets are no longer interesting, and I suspect that within a few years we'll be talking mainly about population of terrestrial planets rather than focusing on individual objects. </p> <div class="Discussion_UserSignature"> </div>
 
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MeteorWayne

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<p>Thanx for pointing out this paper. Yes we have finally reached the point that enough planets have been discovered to derive some meaningful statistics. Bet there are more surprises out there, though <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" /></p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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Rickstar

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<p>I am really hopeful that 10% will rise,dramatically,once we are able to detect&nbsp;earth-sized planets.</p><p>I wonder how much that percentage may increase,once Hubble's new camera is intalled </p><p>& once Kepler has been scouting for a few years & once JWST has been scouting for a few years?!...<br /><br />...then there's GMT,TMT & ELT...can't WAIT to see&nbsp;what sort of&nbsp;atmosphere's surround the terrestrial planets that all these monsters & missions will detect!&nbsp;<img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" /></p> <div class="Discussion_UserSignature"> </div>
 
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