Page Lecture 8: Extrasolar Planets Claire Max October 19, 2010 Astro 18: Planets and Planetary Systems UC Santa Cruz Claire Max October 19, 2010 Astro.

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Lecture 8:Lecture 8:Extrasolar PlanetsExtrasolar Planets

Lecture 8:Lecture 8:Extrasolar PlanetsExtrasolar Planets

Claire MaxClaire MaxOctober 19, 2010October 19, 2010

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

Claire MaxClaire MaxOctober 19, 2010October 19, 2010

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

Predicted weather patterns on HD80606

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PracticalitiesPracticalitiesPracticalitiesPracticalities

• MidtermMidterm

– A week from today; in this room, regular A week from today; in this room, regular timetime

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

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

• Review sessionsReview sessions

– Section meetings this week will be review Section meetings this week will be review sessions for the mid-term examsessions for the mid-term exam

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MidtermMidtermMidtermMidterm

• 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– Newton’s and Kepler’s laws of gravitationNewton’s and Kepler’s laws of gravitation– Radiation (Wavelength/Frequency relation, photon Radiation (Wavelength/Frequency relation, photon

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

– Diffraction limit, Small-angle formulaDiffraction limit, Small-angle formula• Be ready to discuss solar system formation, Be ready to discuss solar system formation,

extrasolar planetsextrasolar planets• Formulas will be given on the exam, but you need to Formulas will be given on the exam, but you need to

know how to know how to use use themthem• BRING YOUR SCIENTIFIC CALCULATOR!BRING YOUR SCIENTIFIC CALCULATOR!

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Outline of lectureOutline of lectureOutline of lectureOutline of lecture

• Almost 500 planet candidates have now Almost 500 planet candidates have now been observed around other starsbeen observed around other stars– 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

Please remind me to Please remind me to take a break at 12:45 take a break at 12:45 pmpm

Known Exoplanets as of Known Exoplanets as of yesterdayyesterdayKnown Exoplanets as of Known Exoplanets as of yesterdayyesterday

• 494 planets 494 planets 

• 416 planetary 416 planetary systems systems 

• 50 multiple planet 50 multiple planet systemssystems

• Hundreds of Hundreds of planets inside planets inside orbit of Earth but orbit of Earth but more massive more massive than Jupiterthan Jupiter

1 1 AUAU 10 10

MMjupjup

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The Main PointsThe Main PointsThe Main PointsThe Main Points

• The ~ 500 planets we have detected to date The ~ 500 planets we have detected to date are only a sub-set of potential planets out are only a sub-set of potential planets out therethere

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

• It’s It’s hard hard to find Earth-like planetsto find Earth-like planets– But prospect of finding Earth-like planets is But prospect of finding Earth-like planets is

thrilling!thrilling!

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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 “paradigm shift”evolution are in midst of a “paradigm shift”– Prevailing ideas of 15 years ago don’t work any Prevailing ideas of 15 years ago don’t work any

more, in light of new datamore, in light of new data– Lots of ferment, discussion, computer Lots of ferment, discussion, computer

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

systems of varying agessystems of varying ages

• A VERY EXCITING TIME!A VERY EXCITING TIME!• Exoplanet Encyclopaedia Exoplanet Encyclopaedia http://www.exoplanet.eu/catalog.php

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

The ancient Greek “atomists” The ancient Greek “atomists” 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, “On the Infinite Universe and Giordano Bruno, “On the Infinite Universe and Worlds”Worlds”

• 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

• Indirect:Indirect: measurements of stellar measurements of stellar properties revealing the effects of properties revealing the effects of orbiting planetsorbiting planets– Most planets to date have been Most planets to date have been detected by indirect methodsdetected by indirect methods

•Direct:Direct: pictures or spectra of the pictures or spectra of the planets themselvesplanets themselves– Only recently starting to be used Only recently starting to be used 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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Observational techniquesObservational techniques

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

DirectDirect● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

DirectDirect

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Observational techniquesObservational techniques

● 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 Sun’s motion The Sun’s motion around the solar around the solar system’s center of system’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 the planets.of all the planets.

Astrometric TechniqueAstrometric TechniqueAstrometric TechniqueAstrometric Technique

• We can detect We can detect planets by planets by measuring the measuring the change in a star’s change in a star’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 TechniqueDoppler TechniqueDoppler TechniqueDoppler Technique

• Measuring a star’s Measuring a star’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

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51 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 planet’s Doppler shift data tell us about a planet’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 planetplanet

PeriodicitPeriodicity depends y depends on period on period of planetof planet

Low massLow mass, , high high massmass

Small 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 star’s spectrumLook for periodic shift in star’s spectrum– Does not depend on distance of starDoes not depend on distance of star– Need Need massivemassive planet planet nearnear star star

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

– Need very good spectrumNeed very good spectrum» measure Doppler shifts of < 1 part in 1,000,000measure Doppler shifts of < 1 part in 1,000,000

• 90% of planet detections to date90% of planet detections to date

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

http://rml3.com/a10p/detecting.htm

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

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

detects velocity along detects velocity along line of sightline of sight– Can’t distinguish Can’t distinguish

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

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://oklo.org/category/exoplanet-detection/

• ““Systemic” console: you participate in Systemic” 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

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● From ground-From ground-based based observatories, observatories, detect shifts > detect shifts > 1-2 m/sec1-2 m/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

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

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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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Observational techniquesObservational techniques

● Doppler spectroscopyDoppler spectroscopy● Transit photometry and Transit photometry and

spectraspectra● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

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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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Animation of transit planet Animation of transit planet detection techniquedetection techniqueAnimation of transit planet Animation of transit planet detection techniquedetection technique

file:///Users/max/Desktop/AY18%202010/Bennett6e_IG_0321634411_PDF/13_Lecture_Outline/IF_13_07_PlanetaryTransits.htm

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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 ~ 70 Thus far ~ 70 planets have been planets have been found this wayfound this way

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

• http://www.transitsearch.org/

Transits and EclipsesTransits and EclipsesTransits and EclipsesTransits and Eclipses

• A A transittransit is when a planet crosses in front of a is when a planet crosses in front of a star.star.

• EclipseEclipse is when a planet goes behind a star is when a planet goes behind a star• From both, can learn about atmosphere of planet From both, can learn about atmosphere of planet

(beginning and end of transit, eclipse)(beginning and end of transit, eclipse)

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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

NASA’s Kepler Space NASA’s Kepler Space Mission to detect transiting Mission to detect transiting planetsplanets

NASA’s Kepler Space NASA’s Kepler Space Mission to detect transiting Mission to detect transiting planetsplanets

• March 2009: NASA mission Kepler was March 2009: NASA mission Kepler was launchedlaunched

• Scans a hundred thousand stars in the Scans a hundred thousand stars in the constellation Cygnus for planets constellation Cygnus for planets

• Measurement precision expected to detect Measurement precision expected to detect and characterize Earth-sized planetsand characterize Earth-sized planets

• Kepler has already been able to detect the Kepler has already been able to detect the light from a known transiting extrasolar light from a known transiting extrasolar gas giant, HAT-P-7bgas giant, HAT-P-7b

• Many discoveries to be announced soonMany discoveries to be announced soon

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Observational techniquesObservational techniques

● Doppler spectroscopyDoppler spectroscopy● Transit photometry and Transit photometry and

spectraspectra● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

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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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Observational techniquesObservational techniques

● Doppler spectroscopyDoppler spectroscopy● Transit photometry and Transit photometry and

spectraspectra● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

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AstrometryAstrometryAstrometryAstrometry

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

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

• No confirmed No confirmed candidates yetcandidates yet

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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

• Sun’s mass is about 1000x Jupiter’s Sun’s mass is about 1000x Jupiter’s massmass

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

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

mass: 0.0052 AUmass: 0.0052 AU

• From nearest star, Sun’s motion From nearest star, Sun’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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Observational techniquesObservational techniques

● Doppler spectroscopyDoppler spectroscopy● Transit photometry and Transit photometry and

spectraspectra● MicrolensingMicrolensing● AstrometryAstrometry● Direct imagingDirect imaging

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Direct ImagingDirect ImagingDirect ImagingDirect Imaging

• Use planet’s own lightUse planet’s 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 This star has 3 orbiting

planets - the first imaged planets - the first imaged planetary planetary systemsystem!!

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

• Adaptive Optics was used Adaptive Optics was used to sharpen imagesto sharpen images

• Observations were Observations were repeated over years, repeated over years, confirming planetary confirming planetary motionmotion

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

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

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

• Adaptive Optics was used Adaptive Optics was used to sharpen imagesto sharpen images

• Observations were Observations were repeated over years, repeated over years, confirming planetary confirming planetary motionmotion

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

Keck Observatory infrared image of star HR8799 and 3orbiting planets; 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 Hubble Space Space Telescope Telescope visible image visible image of the star of the star Fomalhaut Fomalhaut (whose light (whose light was was blocked), blocked), with a dust with a dust belt similar belt similar to the Kuiper to the Kuiper belt. belt.

Inset: Images Inset: Images taken ~2 taken ~2 years apart years apart show a show a planet planet moving moving around the around the star.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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Web list of all planets, Web list of all planets, searchablesearchableWeb list of all planets, Web list of all planets, searchablesearchable

• http://planetquest1.jpl.nasa.gov/atlas/atlas_index.cfm

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Master list of other solar Master list of other solar systemssystemsMaster list of other solar Master list of other solar systemssystems

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One ExampleOne ExampleOne ExampleOne Example

• 50 multi-planet 50 multi-planet systems to datesystems to date

• 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• Much higher eccentricity in most of Much higher eccentricity in most of

their orbitstheir orbits

• Much higher fraction of planets very Much higher fraction of planets very close to their parent starsclose to their parent stars

• Many planets are “super-Jupiters” (up Many planets are “super-Jupiters” (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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Many extrasolar planets Many extrasolar planets are very close to parent are very close to parent starsstars

Many extrasolar planets Many extrasolar planets are very close to parent are very close to parent starsstars

• This is a selection This is a selection effecteffect (caused by (caused by detection method) detection method)

• But it does show that But it does show that such planets exist!such planets exist!

• Our Solar System is Our Solar System is very different (green very different (green points) - Mercury is points) - Mercury is farther away from Sun farther away from Sun than many of the extra-than many of the extra-solar planets are from solar planets are from their starstheir stars

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Characteristics of Extra-Solar Planets: MassCharacteristics of Extra-Solar Planets: Mass

• Many planets Many planets much much moremore massive than massive than JupiterJupiter

• Many planets Many planets much much moremore massive than massive than JupiterJupiter

Selection effect: we are missing planets on the low-mass end

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Patterns in eccentricityPatterns in eccentricityPatterns in eccentricityPatterns in eccentricity

• Most new planets are Most new planets are in elliptical orbitsin elliptical orbits

• Short period planets: Short period planets: – Very close to parent Very close to parent

stars, very low stars, very low eccentricityeccentricity

– Same process that Same process that moved planets close moved planets close to star circularized to star circularized their orbitstheir orbits

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Parent stars of extrasolar Parent stars of extrasolar planetsplanetsParent stars of extrasolar Parent stars of extrasolar planetsplanets

• High in elements High in elements heavier than heavier than hydrogen and hydrogen and helium (usually > helium (usually > Sun)Sun)– reasonable: planetsreasonable: planets

form from dustform from dust

• Probability of finding Probability of finding a planet increases a planet increases as heavy element as heavy element content of parent content of parent star increasesstar increases

PPplanetplanet ~ ~ ((NNFeFe/ N/ NHH))1.61.6

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What are these planets?What are these planets?What are these planets?What are these planets?

• Our Solar System has small rocky planets Our Solar System has small rocky planets close to star, large gas giants further awayclose to star, large gas giants further away– no experience of no experience of large massivelarge massive planets planets close close to to

sun in our Solar Systemsun in our Solar System

• Theory of giant planet formation says they Theory of giant planet formation says they have to form outside “frost line”have to form outside “frost line”

Hot JupitersHot JupitersHot JupitersHot Jupiters

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How are giant extrasolar How are giant extrasolar planets formed?planets formed?How are giant extrasolar How are giant extrasolar planets formed?planets formed?

• Theory for our Solar Theory for our Solar System:System:– Stellar wind from young Sun Stellar wind from young Sun

blew volatiles outwardsblew volatiles outwards– ““Snowstorm” at 5 AU where Snowstorm” at 5 AU where

water-ice solidifiedwater-ice solidified– Fast accretion of large icy Fast accretion of large icy

planet (~10 Mplanet (~10 MEarthEarth) which ) which then collected H/He then collected H/He atmosphereatmosphere» Gas giants Jupiter, Saturn Gas giants Jupiter, Saturn

just outside “frost line”just outside “frost line”» Small rocky planets Small rocky planets

insideinside» Slowly accreting icy Slowly accreting icy

planets in outer system planets in outer system (Uranus, Neptune)(Uranus, Neptune)

• Extrasolar giant planets:Extrasolar giant planets:– Do they form in situ?Do they form in situ?» looks impossible: too hot for looks impossible: too hot for

ices, too little material for ices, too little material for rockrock

– Do they form outside frost Do they form outside frost line and migrate inwards?line and migrate inwards?

» planet forms in gas/dust disc planet forms in gas/dust disc around stararound star

» drag from remaining gas/dust drag from remaining gas/dust causes it to spiral inwardscauses it to spiral inwards

» or scattering from other giant or scattering from other giant planets causes migrationplanets causes migration

» why does it stop?why does it stop?

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This is the “paradigm This is the “paradigm shift”shift”This is the “paradigm This is the “paradigm shift”shift”

• Original theories of solar system formation Original theories of solar system formation developed when our own Solar System was the developed when our own Solar System was the only oneonly one– Mostly circular orbitsMostly circular orbits– Giant planets in outer solar system, terrestrial Giant planets in outer solar system, terrestrial

planets insideplanets inside

• New Solar Systems are (in general) not like oursNew Solar Systems are (in general) not like ours• Needs a new theoryNeeds a new theory• How to arrive at a new paradigm?How to arrive at a new paradigm?

– Mostly use computer simulations to develop ideas, Mostly use computer simulations to develop ideas, test hypotheses, make predictionstest hypotheses, make predictions

– Test predictions against observed young solar Test predictions against observed young solar systems, diskssystems, disks

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Theories for how giant Theories for how giant planets got so close to planets got so close to their starstheir stars

Theories for how giant Theories for how giant planets got so close to planets got so close to their starstheir stars

1.1. Interactions between individual new planets Interactions between individual new planets and gaseous disk. and gaseous disk. ““MigrationMigration””

2.2. After gas disk cleared away, several giant After gas disk cleared away, several giant planets in outer parts of solar system were leftplanets in outer parts of solar system were left– Three-body gravitational interactions between Three-body gravitational interactions between

themthem

– One giant planet got slung outwards, a second was One giant planet got slung outwards, a second was slung inwards and got “captured” by the star in a slung inwards and got “captured” by the star in a close orbitclose orbit

– But why isn’t the close orbit very elliptical?But why isn’t the close orbit very elliptical?

• Why didn’t Jupiter migrate inwards close to Why didn’t Jupiter migrate inwards close to Sun?Sun?

Planetary Migration in a Planetary Migration in a massive diskmassive diskPlanetary Migration in a Planetary Migration in a massive diskmassive disk

• A young planet’s A young planet’s motion can motion can create waves in a create waves in a planet-forming planet-forming disk.disk.

• Models show that Models show that matter in these matter in these waves can tug on waves can tug on a planet, causing a planet, causing its orbit to its orbit to migrate inward.migrate inward.

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1. Planet formation in 1. Planet formation in gaseous diskgaseous disk1. Planet formation in 1. Planet formation in gaseous diskgaseous disk

• One planet in a One planet in a gaseous diskgaseous disk

• Accretion begins, Accretion begins, gap starts to formgap starts to form

• Planet can continue Planet can continue to accrete mass to accrete mass even after a “gap” even after a “gap” in disk has formedin disk has formed

• From computer From computer simulation by Pawel simulation by Pawel CiecielagCiecielag

Hypothesis 2: Hypothesis 2: Gravitational EncountersGravitational EncountersHypothesis 2: Hypothesis 2: Gravitational EncountersGravitational Encounters

• Close gravitational encounters between Close gravitational encounters between two massive planets can eject one planet two massive planets can eject one planet while flinging the other into a highly while flinging the other into a highly elliptical orbit.elliptical orbit.

– Orbit would later have to be circularized (drag?)Orbit would later have to be circularized (drag?)

• Multiple close encounters with smaller Multiple close encounters with smaller planetesimals can also cause inward planetesimals can also cause inward migration.migration.

Orbital ResonancesOrbital ResonancesOrbital ResonancesOrbital Resonances

• Resonances Resonances between planets between planets can also cause can also cause their orbits to their orbits to become more become more elliptical.elliptical.

Thought QuestionThought Question What happens in a gravitational What happens in a gravitational encounter that allows a planet’s encounter that allows a planet’s orbit to move inward?orbit to move inward?

Thought QuestionThought Question What happens in a gravitational What happens in a gravitational encounter that allows a planet’s encounter that allows a planet’s orbit to move inward?orbit to move inward?

A.A. It transfers energy and angular It transfers energy and angular momentum to another object.momentum to another object.

B.B. The gravity of the other object forces The gravity of the other object forces the planet to move inward.the planet to move inward.

C.C. It gains mass from the other object, It gains mass from the other object, causing its gravitational pull to become causing its gravitational pull to become stronger.stronger.

Thought QuestionThought Question What happens in a gravitational What happens in a gravitational encounter that allows a planet’s encounter that allows a planet’s orbit to move inward?orbit to move inward?

Thought QuestionThought Question What happens in a gravitational What happens in a gravitational encounter that allows a planet’s encounter that allows a planet’s orbit to move inward?orbit to move inward?

A.A. It transfers energy and angular It transfers energy and angular momentum to another object.momentum to another object.

B.B. The gravity of the other object forces The gravity of the other object forces the planet to move inward.the planet to move inward.

C.C. It gains mass from the other object, It gains mass from the other object, causing its gravitational pull to become causing its gravitational pull to become stronger.stronger.

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Multi-Planet Interactions as Cause of Planetary Migration Simulation: start with 100 Planet Simulation: start with 100 Planet

“Embryos”“Embryos” Scatter, Collide, Stick, Accrete GasScatter, Collide, Stick, Accrete Gas

ChaosChaosAfter 21.5 Myr:After 21.5 Myr:

After 30 Myr:After 30 Myr:Lone Close-inLone Close-in

Jupiter inJupiter in

Eccentric Orbit.Eccentric Orbit.

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What have we learned?What have we learned?What have we learned?What have we learned?

• Using Doppler shift Using Doppler shift measurements we have measurements we have detected ~ 500 planets detected ~ 500 planets around nearby starsaround nearby stars– massive planets close to massive planets close to

stars, often in eccentric stars, often in eccentric orbitsorbits» not what was expectednot what was expected» may arise when Jupiter-may arise when Jupiter-

like planets migrate like planets migrate inwards after formationinwards after formation

– more likely to find planets more likely to find planets around stars that have around stars that have more heavy elementsmore heavy elements

• What does this imply?What does this imply?– does notdoes not imply that such imply that such

systems are typicalsystems are typical» detection method is biaseddetection method is biased– doesdoes imply that they are imply that they are

possible!possible!– does notdoes not imply that systems imply that systems

like ours are uncommonlike ours are uncommon» Jupiter is barely detectableJupiter is barely detectable– butbut does not provide evidence does not provide evidence

that they are common!that they are common!

• No “other Earths” yet but No “other Earths” yet but we’re getting much closerwe’re getting much closer

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Ambitious space missions Ambitious space missions to detect Earth-like planetsto detect Earth-like planetsAmbitious space missions Ambitious space missions to detect Earth-like planetsto detect Earth-like planets

• COROT (French) COROT (French) In orbit nowIn orbit now

• Kepler (NASA) Kepler (NASA) Launched in Launched in March, 2009March, 2009

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COROT mission is in orbit COROT mission is in orbit nownowCOROT mission is in orbit COROT mission is in orbit nownow

• Planetary transitsPlanetary transits• Will look at Will look at

10,000 stars for 10,000 stars for 150 days150 days

• Earth-like planets Earth-like planets but far awaybut far away

• 7 planets found 7 planets found so farso far

• COROT-7-b: ~ 5-COROT-7-b: ~ 5-10 Earth masses, 10 Earth masses, 1.7 times Earth 1.7 times Earth diameterdiameter

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What is a Habitable What is a Habitable Planet?Planet?What is a Habitable What is a Habitable Planet?Planet?

• Not too Not too bigbig • Not too Not too smallsmall • Not too Not too hothot or too or too

coldcold

A good planet is:A good planet is:

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What does What does “habitable” mean “habitable” mean to you?to you?

What does What does “habitable” mean “habitable” mean to you?to you?

• Right temperatureRight temperature

• Liquid waterLiquid water

• Free oxygen to breathFree oxygen to breath

• Light to keep you warm and to Light to keep you warm and to see bysee by

• Radiation shieldRadiation shield

• Asteroid protection from Asteroid protection from atmosphere and Jupiteratmosphere and Jupiter

Next few slides courtesy of Stephen Next few slides courtesy of Stephen KaneKane

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Things That Affect Things That Affect TemperatureTemperatureThings That Affect Things That Affect TemperatureTemperature

• Want temperature so you can Want temperature so you can have liquid water on the surface have liquid water on the surface of the planetof the planet

Water freezes ->Water boils ->-40°80°120°160°40°0°200°240°280°60°100°140°20°-20°180°220°260°

1.1. Temperature of star Temperature of star

2.2. Distance from the starDistance from the star

3.3. Shape of planet’s orbit: Shape of planet’s orbit: circular or ellipticalcircular or elliptical

4.4. Planet’s atmosphere: Planet’s atmosphere: greenhouse gasesgreenhouse gases

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The Habitable Zone The Habitable Zone for Stars of Various for Stars of Various MassesMasses

The Habitable Zone The Habitable Zone for Stars of Various for Stars of Various MassesMasses

•The Habitable Zone (HZ) in green is the The Habitable Zone (HZ) in green is the distance from a star where liquid water is distance from a star where liquid water is expected to exist on the planets surface. expected to exist on the planets surface.

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QuestionQuestionQuestionQuestion

• NASA has made its goal to find NASA has made its goal to find habitablehabitable planets. (Gas giants don’t planets. (Gas giants don’t “matter” as much….)“matter” as much….)– Do you agree that this should be the main Do you agree that this should be the main

priority?priority?

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The Main PointsThe Main PointsThe Main PointsThe Main Points

• The ~ 500 planets we have detected to date The ~ 500 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

• 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

• Migration and planet-planet interactions play a Migration and planet-planet interactions play a role in reshaping a planetary systemrole in reshaping a planetary system

• 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

• It’s hard to find Earth-like planetsIt’s hard to find Earth-like planets– But prospect of finding Earth-like planets is thrilling!But prospect of finding Earth-like planets is thrilling!

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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 “paradigm evolution are in midst of a “paradigm shift”shift”– Prevailing ideas of 10 years ago don’t Prevailing ideas of 10 years ago don’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!

• Planet formation and solar system Planet formation and solar system evolution are in midst of a “paradigm evolution are in midst of a “paradigm shift”shift”– Prevailing ideas of 10 years ago don’t Prevailing ideas of 10 years ago don’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!