AST 115 1st Edition Lecture 15 Outline of Last Lecture I. Formation of the Outer Planetsa. Jupiterb. Saturnc. Neptuned. UranusII. Formation of the Inner Planetsa. Mercuryb. Venusc. Earthd. MarsIII. Leftover Debris from the Construction ProcessIV. Categories of Changing ClassificationsOutline of Current Lecture I. Extra-Solar Planets (Exoplanets)a. DifficultiesII. Detection Techniquesa. Radial Velocity Methodb. Astrometric Methodc. Stellar Transit Methodd. Gravitational “Microlensing”e. Direct ImagingIII. ResultsIV. Notable discoveriesV. Latest NewsCurrent Lecture Extra-Solar Planets (Exoplanets)o Planets outside our solar systemo Difficulties:- Angular separation between star and planet will be very small- The star will far outshine any of its planetso Because of these difficulties, astronomers realized that indirect methods must beused to discover exoplanets.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Astronomers chose to study nearby stars like our Sun (closer than about 100 lightyears away)o First exoplanet was discovered in 1995 by Mayor and Queioz.- 51 Peg b (about 40 light years away) in the direction of the constellation Pegasus. Detection techniqueso Radial Velocity Method/Doppler Effect- Look at the stellar spectrum from low-altitude, periodic variations in the radial velocity of the parent stars produced by the gravity of the planet (Doppler “Wobble”).- It is more likely to detect massive planets orbiting close to their stars using this method.o Astrometric Method (Wavy “Proper Motion” of Stars)- Nearby stars could be tugged back and forth by a massive object/planet. Its track across the sky can be used to show the existence of an object orbiting the star.o Stellar Transits- Some Exoplanets will have orbits whose planes are in our line of sight of the star.- The exoplanet will periodically pass in front of, or transit its star.- Large diameter exoplanets are more likely to produce decreased brightness of its parent star.o Gravitational “Microlensing”- According to Einstein’s General Theory of Relativity, a solar type star and its exoplanet can cause a temporary brightness flare of a much more distant star as the parent star and its exoplanet pass over it.o Direct Imaging- Technology now exists that can directly image an exoplanet in a wide orbit of a parent star relatively close to us. Resultso Some early “exoplanetary” systems:o Periods and orbit size- The first exoplanets discovered were found quite close to their parent stars.- By Kepler’s 3rd Law, this means that these exoplanets have short periods. If a = 0.1 A.U. Then P (period) is equal to about 10 days.- Amplitude of the Doppler shift tells the relative mass of an exoplanet.- Massive exoplanets were the first to be discovered.- With masses of up to several times Jupiter’s mass, their proximity to their parent stars led to the term “hot Jupiters”.- As techniques have improved with time, lower mass exoplanets have been discovered, located farther from their parent star.o Notable discoveries- Upsilon Andromedae has 3 planetso Search for exoplanets is the search for life beyond Earth. Earth is considered to be in the “habitable” zone (Goldilocks of planets) because it is the perfectdistance from the Sun. This allows for Earth to have water that is not all steam, and also not all ice. Latest newso As of 2015, almost 2,000 exoplanets have been
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