Searching for planets around other stars. Searching for planets around other stars. Searching for other planetary systems this is a hard problem!

Transcription

1 Reading: Chap. 21, Sect Final Exam: Tuesday, December 12; 4:30-6:30PM Homework 10: Due in recitation Dec. 1,4 1 Brief review of last time: Formation of Planetary Systems Observational Clues: evidence from our current Solar System evidence from other stars Collapse of interstellar cloud gravitational collapse, fragmentation spinup and disk formation The Solar Nebula (the SS 4.6 Gyr ago) composition, mass, and temperature structure Planet formation differential condensation & the frost line rocky grains inside, ices outside accretion - growth of planetessimals final sweeping out of material by turn-on of star Jupiter and the Sun the Sun has a luminosity of 4 x10 33 erg/s 2 Searching for other planetary systems this is a hard problem! Jupiter emits at most 8 x10 24 erg/s the Sun emits 500,000,000 times more light than Jupiter viewed from 10 pc, they are separated by 5 arc sec equivalent to 1 candle, 10 feet away from a stadium light bank, viewed from 80 miles away! Searching for planets around other stars p. 3 Searching for planets around other stars p. 4

2 Searching for planets around other stars There are other ways to find them... p. 5 Wobbles of stars from reflex motion: Kepler s 3rd Law 3 M star M planet d 2 P = M star + Mplanet 2 d orbital period [yrs] 6 The "See-Saw" Law Mplanet M star d = star d planet M star center-of-mass d star d planet M planet Mplanet << Mstar star moves in a small orbit measure dstar and you know Mplanet The "Radial Velocity" technique: look for orbital VELOCITY of star around CM Orbital motion: vel + 0 time + 7 Reflex Orbital Motion via reflex orbital motion: precision spectroscopy Credit: R. Pogge, OSU as of today: 666 planets in 503 systems 8 V = 2πd P so V star = 30m s 2π M 1 star d M planet M Jupiter Biggest effect if viewed EDGE ON Tilt of orbit to line-of-sight reduces observed velocity Credit: R. Pogge, OSU

3 Jupiter as an example: 9 V Sun around CM of Solar System = 13 m/s (= 30 mph) Doppler effect of 13 m/s is 1 part in 23,000,000 (! ) varies cyclically over a 12 year cycle very difficult (but not impossible) to measure need stable spectroscope over long time Earth? 9 cm/s! Improved chances for detection (V star bigger): pre The Search is On initial search for ordinary planets P orb ~ months first discovery - 51 Peg (Mayor & Queloz) 10 P orb = days M planet = 0.45 M Jupiter Huge strides 11 now over 549 confirmed extrasolar planetary systems (738 planets) found via Radial Velocities Planet Migration Jupiter-mass planets can t form so close to parent stars. Can form farther out migrate inwards by losing angular momentum to gas within disk 12 many (most) found by Geoff Marcy & Co. Most are massive planets Most have small orbits Many are multiple-planet systems

4 13 14 Are they really planets? or are the velocity variations something else? HD proof of a companion via transits Radial Velocity variable: M = 0.69 ± 0.05 M J P = ± d. and orbits along our line-of-sight so --> planet transits across the star! extrasolar planet detection via precision photometry p. 15 p. 16 Credit: R. Pogge, OSU as of today, number of systems/planets discovered by transits: total: 2076 planetary systems, 2769 planets, 458 multiples from space: 1631 planetary systems, 2280 planets, 6339 candidates

5 The first transiting extrasolar planet: HD p. 18 Discovery by Charbonneau et al Hubble Space Telescope light curve 19 Kepler MISSION CONCEPT A Search for Habitable Planets Earth Earth x 100 Launched 6 March m Schmidt telescope: FOV >100 deg 2 with an array of 42 CCD Optimized for finding habitable planets ( 0.5 to 10 M ) in the HZ ( near 1 AU ) of solar-like stars Continuously and simultaneously monitor 150,000 main-sequence stars Heliocentric orbit for continuous viewing 4 year duration

6 21 Earth-trailing Heliocentric Orbit Kepler field of view 22 Spacecraft orbit Earth Vernal equinox Winter solstice Earth orbit End Year 1 End Year 4 Sun 1 AU Summer solstice Launch: launch June 2008 Autumnal equinox End Year 1 Heliocentric Coordinates End Year 4 Sun!Earth!Spacecraft Period (days)! ! Semi-major (AU)! ! eccentricity! ! Sun-Earth Fixed Coordinates Transiting Planets after Kepler Transiting Planets pre- 23 Fressin N. Batalha NASA-Kepler

7 Kepler 11 - a 6 planet system Kepler 11 artwork 25 Kepler 11 artwork 26 Kepler a system formed 11.2 billion years ago 28 multiple planet systems

8 29 30 Kepler 16b a planet with two suns Kepler 16b a planet with two suns 31 p. 32 the future