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Lesson 15 – Extrasolar PlanetsIn this lecture we're going to look at extra-solar planets, or exoplanets. That means planets orbiting starsother than the Sun. We'll look at the different methods that are being used to detect exoplanets, theseinclude the Doppler method, the Transit method and the Micro-lensing method. We'll look at what types ofplanets have been found, and we'll look at the methods that have been planned to directly detectexoplanets.Site:UNSW MoodleCourse:PHYS1160-Introduction to Astronomy T1 2019Book:Lesson 15 – Extrasolar PlanetsPrinted by:Jack SmithDate:Sunday, 28 April 2019, 5:41 PMLesson 15 – Extrasolar Planets1 of 3528/04/2019, 5:41 pm
Table of contents15 Exoplanets15.1 The Doppler Wobble Method15.2 Microlensing15.3 The Transit Method15.4 Direct Detection15.5 SummaryLesson 15 – Extrasolar Planets2 of 3528/04/2019, 5:41 pm
15 ExoplanetsSHOW WHOLE LESSON AS SINGLE WEB PAGE GO TO FIRST PAGELesson 15 – Extrasolar Planets3 of 3528/04/2019, 5:41 pm
15.1 The Doppler Wobble MethodFinding Planets – The Doppler Wobble WayLet's look at the Doppler or radial velocity method (sometimes also called the Doppler Wobble method) offinding planets. The problem with finding planets around other stars is principally that the planetsthemselves are very, very faint, while the stars they orbit are very, very bright. The planets themselves areso much fainter than the star that we usually can't see the planet.The Doppler method relies on detecting the impact of a planet on the star it orbits, rather light than theplanet itself. This motion is detected using the Doppler effect that we've already looked at for studying aBinary Star System. As one star moves around another in a binary system orbit, its spectral lines will beshifted first to the red and then to the blue, depending on where it is in its orbit. If we have two starsorbiting each other then both stars are actually moving around their common centre of mass. The leastmassive star moves in the largest orbit, and the more massive star also moves in a smaller orbit.The Doppler Wobble or Radial Velocity technique: As the planet movestowards us, the star moves away and is red-shifted. As the planet moves awayfrom us the star moves towards us and is blue-shifted.Exactly the same behaviour happens when a planet orbits a star. Even though the planet is very much lessmassive than the star, the star and the planet both move around their common centre of mass. Because thestar is so much more massive than the planet, the motion of the star is much smaller, but it can still beLesson 15 – Extrasolar Planets4 of 3528/04/2019, 5:41 pm
detected by precise measurements of the Doppler effect. We don't actually see the planet itself, instead

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Term
Three
Professor
Bailey
Tags
Planet, Extrasolar planet, extrasolar planets

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