Download - Lecture 8: Extrasolar Planets

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Lecture 8:Lecture 8:Extrasolar PlanetsExtrasolar Planets

Lecture 8:Lecture 8:Extrasolar PlanetsExtrasolar Planets

Claire MaxClaire MaxApril 29, 2014April 29, 2014

Astro 18: Planets and Planetary SystemsAstro 18: Planets and Planetary SystemsUC Santa CruzUC Santa Cruz

Claire MaxClaire MaxApril 29, 2014April 29, 2014

Astro 18: Planets and Planetary SystemsAstro 18: Planets and Planetary SystemsUC Santa CruzUC Santa Cruz

Predicted weather patterns on HD80606

Please Please remind me to remind me to take a break take a break at 12:45 pm!at 12:45 pm!

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PracticalitiesPracticalitiesPracticalitiesPracticalities

• MidtermMidterm

– May 8May 8thth, week from Thursday; in this room, class , week from Thursday; in this room, class timetime

– Multiple-choice questions (lectures and reading)Multiple-choice questions (lectures and reading)

– Short-answer questions (calculations)Short-answer questions (calculations)

• Review sessionReview session

– I will use the second half of *this Thursday’s I will use the second half of *this Thursday’s lecture* for our review session. lecture* for our review session.

– I will post questions from previous exams on the I will post questions from previous exams on the web before this Thursday. Take a look at them web before this Thursday. Take a look at them ahead of time.ahead of time.

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I am behind on grading I am behind on grading your homework your homework assignmentsassignments

I am behind on grading I am behind on grading your homework your homework assignmentsassignments• II’’m really really sorry! m really really sorry!

– (excuses excuses: no TA, no grader …)(excuses excuses: no TA, no grader …)

• I will do my best to have Homework I will do my best to have Homework 2 graded by class time this 2 graded by class time this Thursday, and Homework 3 graded Thursday, and Homework 3 graded by next Tuesday at the latestby next Tuesday at the latest

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Midterm Thursday May 8Midterm Thursday May 8thth in classin classMidterm Thursday May 8Midterm Thursday May 8thth in classin class• Be ready to do calculations using the following Be ready to do calculations using the following

concepts:concepts:– Kinetic and potential energyKinetic and potential energy– NewtonNewton’’s version of Keplers version of Kepler’’s 3rd laws 3rd law– Radiation (Wavelength/Frequency relation, photon Radiation (Wavelength/Frequency relation, photon

energy, Wien and Stefan-Boltzmannenergy, Wien and Stefan-Boltzmann’’s law, Doppler s law, Doppler shift)shift)

– Telescopes and the diffraction limitTelescopes and the diffraction limit– Small-angle formula and parallaxSmall-angle formula and parallax– Solar System formationSolar System formation

• Some formulas will be given, but you need to know Some formulas will be given, but you need to know how to use themhow to use them

• BRING YOUR SCIENTIFIC CALCULATOR!BRING YOUR SCIENTIFIC CALCULATOR!

Astro Colloquium Wed. Astro Colloquium Wed. (tomorrow) on Extrasolar (tomorrow) on Extrasolar PlanetsPlanets

Astro Colloquium Wed. Astro Colloquium Wed. (tomorrow) on Extrasolar (tomorrow) on Extrasolar PlanetsPlanets

•Prof. Heather Knutson, CaltechProf. Heather Knutson, Caltech““Friends of Hot Jupiters: Friends of Hot Jupiters: A Search for Distant, Massive Companions A Search for Distant, Massive Companions to Close-In Gas Giant Planets”to Close-In Gas Giant Planets”

• Nat Sci Annex room 101, 3:45 – 5pmNat Sci Annex room 101, 3:45 – 5pm–Enter Nat Sci 2 on ground floor beneath Enter Nat Sci 2 on ground floor beneath concrete stairs, turn left into Nat Sci Annexconcrete stairs, turn left into Nat Sci Annex

• If you attend, you can get extra credit on If you attend, you can get extra credit on the next homework by writing a short the next homework by writing a short paragraph on what you learnedparagraph on what you learned

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Outline of lectureOutline of lectureOutline of lectureOutline of lecture

• Almost 1700 planet candidates have Almost 1700 planet candidates have now been observed around other stars; now been observed around other stars; there are another approx. 3700 there are another approx. 3700 candidate planets not yet confirmedcandidate planets not yet confirmed– How have they been detected?How have they been detected?

– What do they look like?What do they look like?

– What do they tell us?What do they tell us?

– What does the future hold?What does the future hold?

With thanks to Susan CartwrightWith thanks to Susan Cartwright

Simulation by Geoff Bryden, JPL:Simulation by Geoff Bryden, JPL:Solar system and disk based on that observed Solar system and disk based on that observed

around the star Gl 876around the star Gl 876

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The Main PointsThe Main PointsThe Main PointsThe Main Points

• The ~ 1700 planets we have detected to date The ~ 1700 planets we have detected to date are only a sub-set of potential planets out thereare only a sub-set of potential planets out there

• Many of the new solar systems don’t look at all Many of the new solar systems don’t look at all like our own (example: Jupiter-mass planets like our own (example: Jupiter-mass planets within the orbit of our Mercury)within the orbit of our Mercury)

• These new solar systems have raised big These new solar systems have raised big questions about how our questions about how our ownown Solar System Solar System formedformed

• Future search methods have high probability of Future search methods have high probability of finding more (and more varied) planetsfinding more (and more varied) planets

• ItIt’’s s hard hard to find Earth-like planetsto find Earth-like planets– But we are starting to find some!But we are starting to find some!

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Main Points, continuedMain Points, continuedMain Points, continuedMain Points, continued

• Planet formation and solar system Planet formation and solar system evolution are in midst of a evolution are in midst of a ““paradigm paradigm shiftshift””– Prevailing ideas of 15 years ago donPrevailing ideas of 15 years ago don’’t t

work any more, in light of new datawork any more, in light of new data– Lots of ferment, discussion, computer Lots of ferment, discussion, computer

simulationssimulations– Ultimately will confront data from other Ultimately will confront data from other

solar systems of varying agessolar systems of varying ages

• A VERY EXCITING TIME!A VERY EXCITING TIME!

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Some key exoplanet Some key exoplanet websiteswebsitesSome key exoplanet Some key exoplanet websiteswebsites

• Exoplanets.org: www.exoplanets.org/Exoplanets.org: www.exoplanets.org/• Exoplanet Encyclopaedia: Exoplanet Encyclopaedia:

www.exoplanet.eduwww.exoplanet.edu• NASA Archive: NASA Archive:

exoplanetarchive.ipac.caltech.eduexoplanetarchive.ipac.caltech.edu• Habitable Zone Gallery: www.hzgallery.org Habitable Zone Gallery: www.hzgallery.org • Open Exoplanet Catalog: Open Exoplanet Catalog:

www.openexoplanetcatalogue.comwww.openexoplanetcatalogue.com• Systemic: oklo.orgSystemic: oklo.org• Kepler mission: Kepler mission:

www.nasa.gov/mission_pages/kepler/www.nasa.gov/mission_pages/kepler/

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The ancient Greek The ancient Greek ““atomistsatomists”” argued that there are other argued that there are other solar systemssolar systems

The ancient Greek The ancient Greek ““atomistsatomists”” argued that there are other argued that there are other solar systemssolar systems

• Leucippus (480 - 420 B.C.)Leucippus (480 - 420 B.C.)

• The worlds come into being as follows: many bodies of all sorts and The worlds come into being as follows: many bodies of all sorts and shapes move from the infinite into a great void; they come together shapes move from the infinite into a great void; they come together there and produce a single whirl, in which, colliding with one another there and produce a single whirl, in which, colliding with one another and revolving in all manner of ways, they begin to separate like to and revolving in all manner of ways, they begin to separate like to like.like.

• Epicurus (341 - 270 B.C.)Epicurus (341 - 270 B.C.)

• There are infinite worlds both like and unlike this world of ours. For There are infinite worlds both like and unlike this world of ours. For the atoms being infinite in number, as was already proven, … there the atoms being infinite in number, as was already proven, … there nowhere exists an obstacle to the infinite number of worlds.nowhere exists an obstacle to the infinite number of worlds.

• Unfortunately, the atomists were overshadowed by Aristotle Unfortunately, the atomists were overshadowed by Aristotle (384 - 322 B.C.) who believed that(384 - 322 B.C.) who believed that

• There cannot be more worlds than one.There cannot be more worlds than one.

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Dangerous to believe in Dangerous to believe in plurality of worlds!plurality of worlds!Dangerous to believe in Dangerous to believe in plurality of worlds!plurality of worlds!

• “This space we declare to be infinite; since neither reason, convenience, possibility, sense-perception nor nature assign to it a limit. In it are an infinity of worlds of the same kind as our own ...”

Giordano Bruno, Giordano Bruno, ““On the Infinite Universe and On the Infinite Universe and WorldsWorlds””

• Unfortunately, plurality of worlds was a heretical idea. Unfortunately, plurality of worlds was a heretical idea. Bruno was burned at the stake in 1600.Bruno was burned at the stake in 1600.

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Why is it so hard to find Why is it so hard to find planets around other stars?planets around other stars?Why is it so hard to find Why is it so hard to find planets around other stars?planets around other stars?

• Faint planet glimmer is lost in glare from parent starFaint planet glimmer is lost in glare from parent star– Planets are small, close to their parent star, and shine by reflected Planets are small, close to their parent star, and shine by reflected

starlightstarlight

• Thought experiment:Thought experiment:– Imagine grain of rice an inch from a 100 Watt light bulb. Someone Imagine grain of rice an inch from a 100 Watt light bulb. Someone

standing at end of a long dark hall would see only the light bulb, not standing at end of a long dark hall would see only the light bulb, not the grain of rice. the grain of rice.

• Consider the case of Jupiter and the Sun:Consider the case of Jupiter and the Sun:– As seen from the nearest star, Alpha Centauri, Jupiter would appear a As seen from the nearest star, Alpha Centauri, Jupiter would appear a

billionth as bright as the Sun.billionth as bright as the Sun.

– Jupiter would also be extremely close to the Sun, only 4 arc sec Jupiter would also be extremely close to the Sun, only 4 arc sec away.away.

• Since all other stars are farther than Alpha Since all other stars are farther than Alpha Centauri, Jupiter would be even harder to detect Centauri, Jupiter would be even harder to detect from other starsfrom other stars

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Planets are very hard to Planets are very hard to observe directly (by detecting observe directly (by detecting their own light)their own light)

Planets are very hard to Planets are very hard to observe directly (by detecting observe directly (by detecting their own light)their own light)

• Planets are too faint compared with their starPlanets are too faint compared with their star– This brown dwarf star is barely visible - and its This brown dwarf star is barely visible - and its

star is faintstar is faint• Planets shine by reflected lightPlanets shine by reflected light

– Planets close to parent stars are brightest, but Planets close to parent stars are brightest, but hardest to seehardest to see

(ground) (space)

Planet DetectionPlanet DetectionPlanet DetectionPlanet Detection

• IndirectIndirect: measurements of stellar : measurements of stellar properties revealing the effects of properties revealing the effects of orbiting planetsorbiting planets

–Stellar radial velocities, motions on the sky, Stellar radial velocities, motions on the sky, dimming of star when planet passes in frontdimming of star when planet passes in front

–Most planets to date have been detected Most planets to date have been detected by indirect methodsby indirect methods

•DirectDirect: pictures or spectra of the : pictures or spectra of the planets themselvesplanets themselves

–Recently starting to be used very Recently starting to be used very successfullysuccessfully

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Observational techniquesObservational techniques

● Doppler spectroscopyDoppler spectroscopy● Transit photometry and spectraTransit photometry and spectra

● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

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● Doppler spectroscopyDoppler spectroscopy● Transit photometry and Transit photometry and spectraspectra

DirectDirect● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

DirectDirect

What properties of extrasolar What properties of extrasolar planets can we measure?planets can we measure?What properties of extrasolar What properties of extrasolar planets can we measure?planets can we measure?

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● Doppler spectroscopyDoppler spectroscopy● Transit photometry and Transit photometry and

spectraspectra● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

Gravitational TugsGravitational TugsGravitational TugsGravitational Tugs

• The Sun and The Sun and Jupiter orbit Jupiter orbit around their around their common center common center of mass.of mass.

• The Sun therefore The Sun therefore wobbles around wobbles around that center of that center of mass with same mass with same period as Jupiter.period as Jupiter.

Gravitational TugsGravitational TugsGravitational TugsGravitational Tugs

• The SunThe Sun’’s motion s motion around the solar around the solar systemsystem’’s center of s center of mass depends on mass depends on tugs from all the tugs from all the planets.planets.

• Astronomers around Astronomers around other stars that other stars that measured this measured this motion could motion could determine the determine the masses and orbits masses and orbits of all of our planets.of all of our planets.

Astrometric TechniqueAstrometric TechniqueAstrometric TechniqueAstrometric Technique

• We can detect We can detect planets by planets by measuring the measuring the change in a starchange in a star’’s s position on sky.position on sky.

• However, these However, these tiny motions are tiny motions are very difficult to very difficult to measure (~ measure (~ 0.001 0.001 arcsecond).arcsecond).

Doppler shift: a moving object can change Doppler shift: a moving object can change frequency of emitted or reflected wavesfrequency of emitted or reflected wavesDoppler shift: a moving object can change Doppler shift: a moving object can change frequency of emitted or reflected wavesfrequency of emitted or reflected waves

Light waves:Light waves:

Doppler TechniqueDoppler TechniqueDoppler TechniqueDoppler Technique

• Measuring a starMeasuring a star’’s s Doppler shift can Doppler shift can tell us its motion tell us its motion toward and away toward and away from us.from us.

• Current Current techniques can techniques can measure motions measure motions as small as 1-2 as small as 1-2 m/s (walking m/s (walking speed!).speed!).

First Extrasolar Planet: 51 First Extrasolar Planet: 51 PegasiPegasiFirst Extrasolar Planet: 51 First Extrasolar Planet: 51 PegasiPegasi

• Doppler shifts of the Doppler shifts of the star 51 Pegasi star 51 Pegasi indirectly revealed a indirectly revealed a planet with 4-day planet with 4-day orbital period.orbital period.

• This short period This short period means that the planet means that the planet has a small orbital has a small orbital distance – well within distance – well within orbit of Mercury.orbit of Mercury.

• This was the first This was the first extrasolar planet to be extrasolar planet to be discovered (1995).discovered (1995).

Insert TCP 6e Figure 13.4a unannotated

Peg b (1995)51 Peg b (1995)51 Peg b (1995)51 Peg b (1995)

Half the mass of Jupiter, yet orbiting much closer to the Sun than Mercury!

Other Extrasolar PlanetsOther Extrasolar PlanetsOther Extrasolar PlanetsOther Extrasolar Planets

• Doppler shift data tell us about a planetDoppler shift data tell us about a planet’’s s mass and the shape of its orbit.mass and the shape of its orbit.

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Stellar wobble depends on mass, Stellar wobble depends on mass, period and eccentricity of planetperiod and eccentricity of planet Stellar wobble depends on mass, Stellar wobble depends on mass, period and eccentricity of planetperiod and eccentricity of planet

Size Size dependdepends on s on mass of mass of planetplanetLow massLow mass, , high high

massmassPeriodicitPeriodicity depends y depends on period on period of planetof planetSmall periodSmall period, , large large

periodperiod

Shape depends Shape depends on eccentricity on eccentricity of planetof planet

CircularCircular, , eccentriceccentric

Planetary signaturesPlanetary signatures

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Doppler shiftDoppler shiftDoppler shiftDoppler shift

• Look for periodic shift in Look for periodic shift in starstar’’s spectrums spectrum– Does not depend on distance of Does not depend on distance of

starstar– Need Need massivemassive planet planet nearnear star star

» the closer the planet, the the closer the planet, the faster the orbital speed (of faster the orbital speed (of both planet and star)both planet and star)

– Need very good spectrumNeed very good spectrum» measure Doppler shifts of < measure Doppler shifts of <

1 part in 1,000,0001 part in 1,000,000

• 90% of planet detections to 90% of planet detections to datedate

• Incredibly hard Incredibly hard measurements have now measurements have now become standardbecome standard

Planet Mass and Orbit TiltPlanet Mass and Orbit TiltPlanet Mass and Orbit TiltPlanet Mass and Orbit Tilt

• We cannot measure an exact mass for a planet We cannot measure an exact mass for a planet without knowing the tilt of its orbit, because without knowing the tilt of its orbit, because Doppler shift tells us only the velocity toward Doppler shift tells us only the velocity toward or away from us.or away from us.

• Doppler data give us lower limits on masses.Doppler data give us lower limits on masses.

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Radial velocity method Radial velocity method doesndoesn’’t give all the orbital t give all the orbital informationinformation

Radial velocity method Radial velocity method doesndoesn’’t give all the orbital t give all the orbital informationinformation• Doppler shift only Doppler shift only

detects velocity along detects velocity along line of sightline of sight– CanCan’’t distinguish massive t distinguish massive

planet (or brown dwarf!) planet (or brown dwarf!) in tilted orbit from less in tilted orbit from less massive planet in edge-massive planet in edge-on orbiton orbit

– They both have the They both have the same line-of-sight same line-of-sight velocityvelocity

• The only way to resolve The only way to resolve this ambiguity is to this ambiguity is to observe using another observe using another methodmethod

WHY?WHY?

Thought QuestionThought Question

Suppose you found a star with the Suppose you found a star with the same mass as the Sun moving back same mass as the Sun moving back and forth with a period of 16 months. and forth with a period of 16 months. What could you conclude?What could you conclude?

Thought QuestionThought Question

Suppose you found a star with the Suppose you found a star with the same mass as the Sun moving back same mass as the Sun moving back and forth with a period of 16 months. and forth with a period of 16 months. What could you conclude?What could you conclude?A.A. It has a planet orbiting at less than 1 It has a planet orbiting at less than 1

AU.AU.

B.B. It has a planet orbiting at greater than It has a planet orbiting at greater than 1 AU.1 AU.

C.C. It has a planet orbiting at exactly 1 AU.It has a planet orbiting at exactly 1 AU.

D.D. It has a planet, but we do not have It has a planet, but we do not have enough information to know its orbital enough information to know its orbital distance.distance.

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Find your own Find your own planet!planet!Find your own Find your own planet!planet!

•http://www.stefanom.org/systemic/

• ““SystemicSystemic”” console: you participate in console: you participate in finding signals of planets from telescope finding signals of planets from telescope data that others have obtaineddata that others have obtained

http://www.stefanom.org/systemic/

http://www.stefanom.org/systemic/

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● From ground-From ground-based based observatories, observatories, detect velocity detect velocity shifts > 1-2 shifts > 1-2 m/secm/sec

● The nearer to The nearer to the star and the the star and the more massive more massive the planet, the the planet, the easier to detecteasier to detect

● Corresponds to Corresponds to about 33 earth about 33 earth masses at 1 AU masses at 1 AU for a solar mass for a solar mass star.star.

Limitations of Doppler techniqueLimitations of Doppler techniqueLimitations of Doppler techniqueLimitations of Doppler technique

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Earth

Hot Jupiters!

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Huge number of new exoplanets, due to Kepler transit mission

Huge number of new exoplanets, due to Kepler transit mission

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TransitsTransitsTransitsTransits

• As planet moves across face of star, it As planet moves across face of star, it blocks a tiny bit of starlightblocks a tiny bit of starlight

• Watch for periodic dimming of starWatch for periodic dimming of star

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Planet detected around Planet detected around the star HD209458 by the star HD209458 by transit methodtransit method

Planet detected around Planet detected around the star HD209458 by the star HD209458 by transit methodtransit method

• Planet is 70% mass Planet is 70% mass of Jupiter, but of Jupiter, but orbits in just 3.5 orbits in just 3.5 daysdays

• So it is very close So it is very close to its parent starto its parent star

• Thus far 33 planets Thus far 33 planets have been found have been found this waythis way

• Amateur Amateur astronomers have astronomers have organized to watch organized to watch for fluctuations in for fluctuations in star brightnessstar brightness

Transits and EclipsesTransits and EclipsesTransits and EclipsesTransits and Eclipses

• A A transittransit is when a planet crosses in front of a star.is when a planet crosses in front of a star.• The resulting eclipse reduces the starThe resulting eclipse reduces the star’’s apparent s apparent

brightness and tells us planetbrightness and tells us planet’’s radius.s radius.• No orbital tilt: accurate measurement of planet massNo orbital tilt: accurate measurement of planet mass

observerA transit is more likely observed when the planet is close to its star. This tecnique is best for close-in, large planets.

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Transiting planetsTransiting planetsTransiting planetsTransiting planets

• Can measure size, mass, temperature Can measure size, mass, temperature and spectraand spectra

• Can test the atmospheric models that Can test the atmospheric models that have been developed for planets in our have been developed for planets in our solar systemsolar system

• Some of these planets are subject to Some of these planets are subject to more exciting conditions than the ones more exciting conditions than the ones in the Solar System:in the Solar System:

– Small distance from starSmall distance from star

– Extreme eccentricitiesExtreme eccentricities

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HD 209458bHD 209458bHD 209458bHD 209458bWe have detected both the planet’satmosphere and a “cometary” tail

Orbit: very close to star (1/10th of Mercury’s distance from Sun)

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HD 209458bHD 209458b

• Detection of Detection of Hydrogen, Sodium, Hydrogen, Sodium, Carbon and OxygenCarbon and Oxygen

• Compatible with Compatible with ““Cometary-typeCometary-type”” atmosphereatmosphere

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Otto Struve advocated these techniques in 1952!

"An intrinsically improbable event may

become highly probable if the number of events is very great. ... [I]t is probable that a good

many of the billions of planets in the Milky

Way support intelligent forms of life.”

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Method three: Microlensing Method three: Microlensing

• Background: Microlensing around a star (or Background: Microlensing around a star (or black hole)black hole)

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Needs almost perfect alignment between source and lens.

One-time events!

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Planet detection: fine structure on Planet detection: fine structure on microlensing light curvemicrolensing light curve

• Candidates for several Candidates for several planets have been planets have been discovered this waydiscovered this way

• Potentially very Potentially very useful: can detect useful: can detect planets at large planets at large distances from usdistances from us– Even farther away than Even farther away than

transit method cantransit method can

– Much farther than Much farther than radial velocity or radial velocity or astrometry canastrometry can

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AstrometryAstrometryAstrometryAstrometry

• Look for star moving Look for star moving on the sky (with on the sky (with respect to other stars)respect to other stars)

• Need to measure Need to measure angles (motion on angles (motion on sky) of < 10sky) of < 10-4-4 arc secondsarc seconds

• This is very difficult, This is very difficult, but will be possible in but will be possible in futurefuture

• No confirmed No confirmed candidates yetcandidates yet

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Finding invisible planets Finding invisible planets via the wobble of their via the wobble of their parent starparent star

Finding invisible planets Finding invisible planets via the wobble of their via the wobble of their parent starparent star

• Gravitational force is mutual: planet pulls on Gravitational force is mutual: planet pulls on star star as much as star on planetas much as star on planet– Star and planet both move around system center Star and planet both move around system center

of massof mass

» Star changes position in the plane of the sky Star changes position in the plane of the sky (astrometry)(astrometry)

» Star moves along line of sight (radial velocity)Star moves along line of sight (radial velocity)

– Problem: star is much more massive than planetProblem: star is much more massive than planet

» so wonso won’’t move very much, or very quicklyt move very much, or very quickly

• Need Need veryvery sensitive measurements of sensitive measurements of position on sky (astrometry) and/or velocity position on sky (astrometry) and/or velocity (via Doppler shift of star(via Doppler shift of star’’s spectral lines)s spectral lines)

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Sensitivity needed for astrometry Sensitivity needed for astrometry detection of Jupiter around our Sundetection of Jupiter around our SunSensitivity needed for astrometry Sensitivity needed for astrometry detection of Jupiter around our Sundetection of Jupiter around our Sun

• SunSun’’s mass is about 1000x Jupiters mass is about 1000x Jupiter’’s s massmass

• Astrometric accuracy needed:Astrometric accuracy needed:– Radius of JupiterRadius of Jupiter’’s orbit around center of s orbit around center of

mass: 5.2 AUmass: 5.2 AU– Radius of SunRadius of Sun’’s orbit around center of s orbit around center of

mass: 0.0052 AUmass: 0.0052 AU

• From nearest star, SunFrom nearest star, Sun’’s motion s motion on the sky is like a penny seen on the sky is like a penny seen from 600 km away!from 600 km away!

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Planetary art

Collage by Willy Benz

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Direct DetectionDirect DetectionDirect DetectionDirect Detection

• Use planetUse planet’’s own lights own light• Take image of itTake image of it

– Can reconstruct full Can reconstruct full orbit by watching it go orbit by watching it go aroundaround

• Can also obtain Can also obtain spectraspectra– Learn about physical Learn about physical

conditions, conditions, atmosphere, maybe atmosphere, maybe even presence of lifeeven presence of life

• Jupiter is a billion Jupiter is a billion times fainter than the times fainter than the Sun, in visible light!Sun, in visible light!

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Marois et al. 2008, Science Magazine

First Images of Exoplanets: First Images of Exoplanets: HR 8799 Solar SystemHR 8799 Solar System

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Glowing young planetsGlowing young planets• This star has 3 orbiting planets

- the first imaged planetary system!

• Advanced observing techniques were used to block the star’s light

• Adaptive Optics was used to sharpen images

• Observations were repeated over years, confirming planetary motion

• The planets are young and hot, and therefore glow more brightly than by reflected starlight alone

• This star has 3 orbiting planets - the first imaged planetary system!

• Advanced observing techniques were used to block the star’s light

• Adaptive Optics was used to sharpen images

• Observations were repeated over years, confirming planetary motion

• The planets are young and hot, and therefore glow more brightly than by reflected starlight alone

Keck Observatory infrared image of star HR8799 and three orbiting planets with orbital directions indicated by arrows. The light from the star was subtracted, but a lot of ‘noise’ remains.

Three planets orbiting HR8799

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Hubble Space Telescope visible image of the star Fomalhaut (whose light was blocked), with a dust belt similar to the Kuiper belt. Inset: Images taken ~2 years apart show a planet moving around the star.

Star location

Neptune-sizedorbit

First images of exoplanets: First images of exoplanets: FomalhautFomalhautFirst images of exoplanets: First images of exoplanets: FomalhautFomalhaut

http://dps.aas.org/education/dpsdisc/

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Adaptive optics image of Kappa Andromeda b

Subaru Telescope, Mauna Kea Hawaii

Directly imaged planet around Directly imaged planet around the star Kappa Andromedaethe star Kappa AndromedaeDirectly imaged planet around Directly imaged planet around the star Kappa Andromedaethe star Kappa Andromedae

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Adaptive optics image of the star Beta Pictoris

Gemini South Telescope, Chile

Gemini Planet Imager

Directly imaged planet around Directly imaged planet around the star Beta Pictoristhe star Beta PictorisDirectly imaged planet around Directly imaged planet around the star Beta Pictoristhe star Beta Pictoris

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Web lists of all planets, Web lists of all planets, searchablesearchableWeb lists of all planets, Web lists of all planets, searchablesearchable

• Exoplanets.org: www.exoplanets.org/Exoplanets.org: www.exoplanets.org/• Exoplanet Encyclopaedia: Exoplanet Encyclopaedia:

www.exoplanet.edu

• These sites are continually updated as new These sites are continually updated as new planets are discoveredplanets are discovered

http://www.exoplanet.edu/

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Multi-planet solar system Multi-planet solar system discovered by Doppler discovered by Doppler methodmethod

Multi-planet solar system Multi-planet solar system discovered by Doppler discovered by Doppler methodmethod

• Upsilon Upsilon AndromedaeAndromedae

• Three-planet Three-planet systemsystem

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Upsilon AndromedaeUpsilon AndromedaeUpsilon AndromedaeUpsilon Andromedae

• Two planets are several times more massive than JupiterTwo planets are several times more massive than Jupiter

• The third planet, mass 75% that of Jupiter, is so close to The third planet, mass 75% that of Jupiter, is so close to the star that it completes a full orbit every 4.6 Earth daysthe star that it completes a full orbit every 4.6 Earth days

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The GJ581 systemThe GJ581 systemThe GJ581 systemThe GJ581 system

b

c

• Three planets Three planets of 15, 5 and 7 of 15, 5 and 7 Earth massesEarth masses

• Small, red starSmall, red star

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QuestionsQuestionsQuestionsQuestions

• Has the discovery of other solar systems Has the discovery of other solar systems changed your own feelings about the changed your own feelings about the universe?universe?

• Are you comfortable or uncomfortable Are you comfortable or uncomfortable with the idea that they are so different with the idea that they are so different from our own?from our own?

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Unanticipated Unanticipated characteristics of extra-characteristics of extra-solar planetssolar planets

Unanticipated Unanticipated characteristics of extra-characteristics of extra-solar planetssolar planets• Many have higher eccentricity in most Many have higher eccentricity in most

of their orbitsof their orbits

• Higher fraction of planets very close to Higher fraction of planets very close to their parent starstheir parent stars

• Many planets are Many planets are ““super-Jupiterssuper-Jupiters”” (up (up to 10 times more massive than Jupiter)to 10 times more massive than Jupiter)

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Eccentric OrbitsEccentric OrbitsEccentric OrbitsEccentric Orbits

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The Main PointsThe Main PointsThe Main PointsThe Main Points

• The ~ 1700 planets we have detected to date The ~ 1700 planets we have detected to date are only a sub-set of potential planets out thereare only a sub-set of potential planets out there

• Many of the new solar systems don’t look at all Many of the new solar systems don’t look at all like our own (example: Jupiter-mass planets like our own (example: Jupiter-mass planets within the orbit of our Mercury)within the orbit of our Mercury)

• These new solar systems have raised big These new solar systems have raised big questions about how our questions about how our ownown Solar System Solar System formedformed

• Future search methods have high probability of Future search methods have high probability of finding more (and more varied) planetsfinding more (and more varied) planets

• ItIt’’s s hard hard to find Earth-like planetsto find Earth-like planets– But we are starting to find some!But we are starting to find some!

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Thursday’s lecture will Thursday’s lecture will continue exoplanet discussioncontinue exoplanet discussionThursday’s lecture will Thursday’s lecture will continue exoplanet discussioncontinue exoplanet discussion

•What we are learning about What we are learning about atmospheres, orbits, origins of atmospheres, orbits, origins of extrasolar planetsextrasolar planets

Download - Lecture 8: Extrasolar Planets

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