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Chapter 13 - Exoplanets (2) - 11/30/2009 Extrasolar planets...

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11/30/20091Extrasolar planetsAstronomy 96011Topics to be coveredAll of them (note that many have come a longithttbkitt)way since the textbook was written)2
11/30/2009What is a planet? What is a star?
2I thtl bdb tltIs there a natural boundary between planetsand stars?3Planets and brown dwarfsA star of mass less than 8% ofthe Sun (80x Jupiter’s mass)will never grow hot enough inits core to fuse hydrogenSteady luminosity due to H burningLuminosity “bump” due to short-lived deuterium burningThis is used as the boundarybetween true stars and verylarge gas planetsObjects below this mass arecalledbrown dwarfsThe boundary between BDand planet is morecontroversialsome argue it should besome argue it should bebased on formationother choose 0.013 solarmasses=13 Mjas theboundary, as objects belowthis mass will never reacheven deuterium fusionNelson et al., 1986, AJ, 311, 2264
11/30/200935Worlds Beyond Our SunIn 1995 a team of Swissastronomers discoveredthfitlt (ithe first planet (in a non-pulsar system) outsideour solar system, orbitinga sun-like star called 51Pegasi.Further discoveries bringthe grand total of knownextrasolar planets to 404(as of Nov 25 2009) andcounting.Artist's rendition ofthe star 51 Pegasi andits planetary companion 51 Pegasi B.6
11/30/20094Unseen CompanionsCuriously enough, mostextrasolar planetsextrasolar planetsremain unseenThey are usuallydetected by indirectmeans, though theireffects on their parenteffects on their parentstar.This artist's concept shows theNeptune-sized extrasolar planetcircling the star Gliese 436.7Obstacles to Direct DetectionDirect detection is the only way to tell what these planetsare made of and whether there's water or oxygen in theiratmospheres.But most known exoplanets are impossible to see withcurrent technologyTwo reasons why:known exoplanets are too dimJupiter, for example, is more than a billion times fainter than theSun. However it could easily be seen at large distances except for…known exoplanets orbit too close to their parent starsknown exoplanets orbit too close to their parent starsmost known exoplanets have orbits smaller than that of Mercury"It's like trying to see a firefly next to a searchlight from across town."8
11/30/20095Detection methods: Astrometryoldest method,used since 1943thbblthe wobbleinduced in theplaneofskymotion of the starby planets ismeasured byaccuratelyobserving itsposition over timeno success9Astrometry:Difficulties•Example: The Sunwobbles by about itsdittl dtdiameter, mostly due toJupiter.

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Term
Winter
Professor
AA
Tags
Astronomy, Solar System, Extrasolar planet

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