AST 301Introduction to AstronomyJohn LacyRLM [email protected] LiRLM [email protected] JeonRLM [email protected] site: www.as.utexas.eduGo to Department of Astronomy courses,AST 301 (Lacy), course websiteTopics for this weekArea and volumeFinding extrasolar planetsImagingAstrometric techniqueDoppler techniqueTransit techniqueWhat is foundMassesOrbitsDensities and compositionsFormation of extrasolar planetsReading for next week: ch. 14.2 & 15What sorts of planets have we found?What are their orbits like?What are their masses?How about lower masses?Any planets like the Earth? (0.003 MJ)Differences from our planetary system1. (Almost) no terrestrial mass planets2. Many planets more massive than Jupiter3. Jovian mass planets in small orbits4. Eccentric (non-circular) orbits are common5. At least one star has planets in orbits tipped relative toeach otherCan we explain these planets with our theory of theformation of the solar system?Selection effectsSome of these results are due to biases in ourobservations.Massive planets have more effect on their stars.It is almost impossible for us to detect the motion of a stardue to the pull of a terrestrial planet.Planets close to their stars cause their stars to move faster,causing bigger Doppler shifts.(But since their periods are short, the distance the starsmove is smaller than for planets in big orbits, so motionsin the sky should be harder to observe.)We still need to explainHow gas giant planets can be in orbits close to their starsWhy eccentric orbits are common elsewhere, but not in thesolar systemMaybe how planets more massive than Jupiter can form‘Hot Jupiters’ – Gas giants close to starsMaybe they formed there, but not by starting with an icycore.Stars gather most of their masses by gravitational collapse:gravity pulled the gas cloud they formed from together.Maybe some massive planets formed in a similar way.Or maybe they formed starting with an icy core farther fromtheir star, and then migrated inward.A massive planet can pull on the gas in the disk around it,giving some of its orbital energy to the gas. This couldcause the planet to spiral inward, like a reenteringsatellite.But then why wouldn’t it spiral the whole way in to its
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