Astro 101 11-24

Astro 101 11-24 - Orbits of Extrasolar planets Most of the...

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Astro 101 11-24 Exoplanets: What’s the big deal? Sun-like star is about a billion times brighter than the sunlight reflected from its planets A brief history of exoplanets – Giordano Bruno – Executed in 1600 1995 First discovery Gravitational Tugs Sun and Jupiter orbit around their common center of mass Sun therefore wobbles around that center of mass with same period as Jupiter Astrometric Technique We can detect planets by measuring the change in a star’s position on sky However, these tiny motions are very difficult to measure (.001 arcsecond) Doppler Technique Measuring a star’s Doppler shift can tell us its motion toward and away from us Current techniques can measure motion as small as 1m/s First extrasolar planet Doppler shifts of star 51 Pegasi indirectly reveal a planet with 4 day orbital period Short period means Planet around 51 Pegasi has a mass similar to Jupiter’s despite its small orbital distance Doppler data curve tells us about a planet’s mass and the shape of its orbit
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Unformatted text preview: Orbits of Extrasolar planets Most of the detected planets have orbits smaller than Jupiter’s Planets at greater distances are harder to detect Orbits of some extrasolar planets are much more elongated, greater eccentricity than those in our solar system Nebular theory of planet formation Developed by Kant in 1755 Predicts that massive Jupiter like planets should nto form inside frost line at<< 5 AU Discovery of hot jupiters has forced reexamination of nebular theory Planetary migration or gravitational encounters may explain hot jupiters 55 Cancri Planet Mass and Orbit Tilt We cannot measure an exact mass for a planet without knowing the tilt of its orbit, because Doppler shift tells us only the velocity toward or away from us Doppler data gives us lower limits on masses Planets are opaque Mass + size = density...
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This note was uploaded on 12/13/2008 for the course ASTRO 1101 taught by Professor Lloyd,j during the Fall '07 term at Cornell.

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Astro 101 11-24 - Orbits of Extrasolar planets Most of the...

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