Andrew Collier Cameron University of St Andrews. Are we alone in the Universe? The plurality of worlds In some worlds there is no Sun and Moon, in others

Andrew Collier CameronUniversity of St Andrews

Are we alone in the Universe?Are we alone in the Universe?The plurality of worldsThe plurality of worlds

• In some worlds there is no Sun and In some worlds there is no Sun and Moon, in others they are larger than in Moon, in others they are larger than in our world, and in others more our world, and in others more numerous. In some parts there are numerous. In some parts there are more worlds, in others fewer (...); in more worlds, in others fewer (...); in some parts they are arising, in others some parts they are arising, in others failing. There are some worlds devoid failing. There are some worlds devoid of living creatures or plants or any of living creatures or plants or any moisture. moisture.

– Democritus (ca. 460-370 B.C.), after Hyppolytus Democritus (ca. 460-370 B.C.), after Hyppolytus (3rd cent. A.D.)(3rd cent. A.D.)

• There cannot be more worlds than one. There cannot be more worlds than one. – Aristotle [ De Caelo ] Aristotle [ De Caelo ]

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

– Leucippus (480-420(?) B.C.), after Leucippus (480-420(?) B.C.), after Diogenes Laertios (3rd cent. A.D.)Diogenes Laertios (3rd cent. A.D.)

How do How do galaxiesgalaxies, stars and planets form , stars and planets form and evolve?and evolve?

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Dusty discs around young starsDusty discs around young stars

• Roughly half of all Roughly half of all new-born Sun-like new-born Sun-like stars are surrounded stars are surrounded by solar system-sized by solar system-sized dusty discs.dusty discs.

• Could this mean that Could this mean that half of all Sun-like half of all Sun-like stars have planetary stars have planetary systems?systems?

Proto-planetary discs in the Orion Nebula (NASA/STScI)

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Searching for extra-solar JupitersSearching for extra-solar Jupiters• A planet and its parent A planet and its parent

star orbit round their star orbit round their common centre of common centre of gravity.gravity.

• The star is much more The star is much more massive than the planet, massive than the planet, so the reflex orbital so the reflex orbital speed is small.speed is small.

• A massive planet in a A massive planet in a close orbit gives its star a close orbit gives its star a reflex velocity of a few reflex velocity of a few tens of mstens of ms–1–1..

• This gives a small but This gives a small but measurable measurable Doppler shiftDoppler shift..

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51 Pegasi: The first wobbling star51 Pegasi: The first wobbling star

Discovered by Michel Mayor& Didier Quelozin mid-1995.

Today’s state Today’s state of playof play

• 237 planets in 203 237 planets in 203 systems, Oct 1995 - systems, Oct 1995 - 20-Aug-2007 from 20-Aug-2007 from “Doppler wobble” “Doppler wobble” searches.searches.

• 25 multiple systems25 multiple systems• 24 transiting 24 transiting

systems, 19 from systems, 19 from transit searchestransit searches

• 4 microlensing 4 microlensing planets (more planets (more distant!)distant!)

Recipe for building JupitersRecipe for building Jupiters• Ingredients:Ingredients:

– 10 Earth masses of ice-coated dust 10 Earth masses of ice-coated dust particlesparticles

– Lots of gas (mostly hydrogen)Lots of gas (mostly hydrogen)

• Method:Method:– Allow dust & ice to coagulateAllow dust & ice to coagulate

– Allow solid core to sweep up gasAllow solid core to sweep up gas

– Leave to cool for 5 billion yearsLeave to cool for 5 billion years

• Common problems:Common problems:– Tidal gaps starve planet of gas.Tidal gaps starve planet of gas.

– Gas accretion takes tens of millions of Gas accretion takes tens of millions of years, longer than lifetime of disc.years, longer than lifetime of disc.

– Migrating planets spiral into star.Migrating planets spiral into star.

Numerical simulation by Pawel Artymowicz, Stockholm.

Tip of the iceberg?Tip of the iceberg?• Left panel: Core Left panel: Core

accretion+migration accretion+migration simulation by Ida & Lin simulation by Ida & Lin (2004), showing (2004), showing gas giants,gas giants, ice giants,ice giants, rocky planets.rocky planets.

• Right panel: Radial-velocity Right panel: Radial-velocity discoveries so far.discoveries so far.

Iron abundance and planet formationIron abundance and planet formation

Eccentric Eccentric OrbitsOrbits

Planet-planet interactions

Eccentricity pumping

Small planets ejected

Tidal circularisation

Unclear why.

Other planet-building recipesOther planet-building recipes

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• If disk cools efficiently by If disk cools efficiently by infrared radiation, infrared radiation, fragments can collapse fragments can collapse spontaneously to form spontaneously to form “instant planets”.“instant planets”.

• Several dozen planets Several dozen planets form and interact.form and interact.

Numerical simulation by Ken Rice, University of St Andrews.

Other planet-building recipesOther planet-building recipes• If disk cools efficiently by If disk cools efficiently by

infrared radiation, infrared radiation, fragments can collapse fragments can collapse spontaneously to form spontaneously to form “instant planets”.“instant planets”.

• Several dozen planets Several dozen planets form and interact.form and interact.

• Smaller planets get Smaller planets get ejected from system.ejected from system.

• One “big fish” survives One “big fish” survives in an eccentric orbit.in an eccentric orbit.

• Problems:Problems:– Hard to get multiple, smaller Hard to get multiple, smaller

planets to survive in near planets to survive in near circular orbits.circular orbits.

Only one planetary object remains after N-body evolution for 21 Myr.

• Mp = 7.4 Jupiter masses

• a = 1.66 au

• e = 0.63

Lessons from Doppler WobblesLessons from Doppler Wobbles

• > 5% of Sun-like stars host a Jupiter> 5% of Sun-like stars host a Jupiter

• Metallicity mattersMetallicity matters

• Orbits differ from Solar SystemOrbits differ from Solar System– wide range of orbit radii ( P > 2d )wide range of orbit radii ( P > 2d )

– wide range of eccentricitieswide range of eccentricities

• New processesNew processes– Migration -- spiral-inMigration -- spiral-in

– eccentricity pumpingeccentricity pumping

– ejectionejection

• What sort of planets are the hot Jupiters ?What sort of planets are the hot Jupiters ?

Transit Transit LightcurvesLightcurves

€

rJup ≈ 0.1RSunDepth :

Δf

f≈1%

rprJup

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

2

R∗RSun

⎛

⎝ ⎜

⎞

⎠ ⎟

−2

Duration :

Δt ≈ 3hM∗

MSun

⎛

⎝ ⎜

⎞

⎠ ⎟

2 / 3P

4d

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 3

Probability :

Pt ≈10%R∗RSun

⎛

⎝ ⎜

⎞

⎠ ⎟M∗

MSun

⎛

⎝ ⎜

⎞

⎠ ⎟

−1/ 3P

4d

⎛

⎝ ⎜

⎞

⎠ ⎟−2 / 3

SuperWASP hardwareSuperWASP hardware

• Pollacco et al 2006, PASP 118, Pollacco et al 2006, PASP 118, 14071407

• LensesLenses– Canon 200mm f/1.8Canon 200mm f/1.8

– Aperture 11.1 cmAperture 11.1 cm

• CCD DetectorCCD Detector– 2048 x 2048 thinned e2v (Andor, 2048 x 2048 thinned e2v (Andor,

Belfast)Belfast)

– 13.5x13.5 micron pixels 13.5x13.5 micron pixels

• Field of ViewField of View– 7.8 x 7.8 degrees7.8 x 7.8 degrees

– 13.7 arcsec/pixel13.7 arcsec/pixel

• MountMount– OMI/Torus robotic mountOMI/Torus robotic mount

• Operating TemperatureOperating Temperature– ––50 50 ººCC

– 3-stage Peltier Cooling3-stage Peltier Cooling

Flatfield

Bias

Dark Current

Exposure Map

Field recognition,astrometry,

aperture photometry,

calibration/de-trending

Flux-RMS

Pre-processed

Raw

12

16h43+31d26 field 2004 May-Aug

0.001

0.01

0.1

1

9 10 11 12 13 14

WASP V magnitude

RMS scatter (mag)

Series1

WASP data reduction pipelineWASP data reduction pipeline

Data processed so far (stellar density plot)

Current Observing fields

Substellar mass-radius relationSubstellar mass-radius relation

Mass-radius relation for hot Mass-radius relation for hot JupitersJupiters

• WASP-1b,-2b: Cameron et al 2007, MNRASWASP-1b,-2b: Cameron et al 2007, MNRAS

(+ XO-2b, HAT-P-2b, HAT-P-3b, TrES-3, TrES-4, CoRoT-EXO-1b, Gl 436b since 2007 May 1)

Why we need many more …Why we need many more …

• How does planet radius scale withHow does planet radius scale with– Planet mass? (Fortney et al 2007)Planet mass? (Fortney et al 2007)

– Planet age? (Many!)Planet age? (Many!)

– Metallicity/opacity? (Burrows et al 2007, Guillot et al 2006)Metallicity/opacity? (Burrows et al 2007, Guillot et al 2006)

– Existence/size of core? (Guillot et al 2006)Existence/size of core? (Guillot et al 2006)

– Proximity to host star? (Fortney et al 2007)Proximity to host star? (Fortney et al 2007)

– Migration history?Migration history?

– ? ?

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Core mass and Core mass and formation formation

mechanismmechanism

• Recent example:Recent example:– HD 149026bHD 149026b– Transiting hot SaturnTransiting hot Saturn– High density => massive coreHigh density => massive core– Sato et al, ApJ, in pressSato et al, ApJ, in press

• Test formation models: Test formation models: – Core accretion+migrationCore accretion+migration– Gravitational instabilityGravitational instability

GJ 436 bGJ 436 b• Gillon et al 2007 May 17, astro-Gillon et al 2007 May 17, astro-

ph/0705.2219ph/0705.2219

• Neptune-mass planetNeptune-mass planet

• Neptune-like radiusNeptune-like radius

• Radius depends strongly on Radius depends strongly on composition (cf. Fortney et al composition (cf. Fortney et al 2007, astro-ph/0612671)2007, astro-ph/0612671)

• Ice-giant structure.Ice-giant structure.

WASP-1b

WASP-2b

Cool PlanetsHot Planets

~100 Doppler wobble planets

Exoplanet “Discovery Space”Exoplanet “Discovery Space”

Microlensing by a starMicrolensing by a star

• Light from background stars is gravitationally bent Light from background stars is gravitationally bent around a foreground star.around a foreground star.

• Light is amplified near the “Einstein Ring”.Light is amplified near the “Einstein Ring”.

• Misaligned objects produce 2 images, one inside and Misaligned objects produce 2 images, one inside and one outside the Einstein Ringone outside the Einstein Ring

Background

Lensing starObserver

Now if I had a REALLY big Now if I had a REALLY big telescope...telescope...

• ...this is what a Sun-...this is what a Sun-like star would do to like star would do to the view of dust the view of dust clouds in a nearby clouds in a nearby galaxy, 150,000 ly galaxy, 150,000 ly away.away.

• The The Einstein ringEinstein ring of of the star is about the the star is about the size of Jupiter’s size of Jupiter’s orbit round the Sun.orbit round the Sun.

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First definitive planetary lens event!First definitive planetary lens event!

• OGLE/PLANET/MOA OGLE/PLANET/MOA collaborationcollaboration

– 45 microlensing events 45 microlensing events monitored intensively over monitored intensively over the last 5 years.the last 5 years.

– No convincing Jupiter-like No convincing Jupiter-like secondary peaks found… secondary peaks found… until last week! until last week!

– Conclusion: less than 30% Conclusion: less than 30% of lensing stars have of lensing stars have Jupiters.Jupiters.

• First definitive planet First definitive planet detection announced in detection announced in NASA press release by NASA press release by D. Bennett’s team, 2004 D. Bennett’s team, 2004 April 15.April 15.

Courtesy Dave Bennett and OGLE/PLANET/MOA team members

OGLE-2003-BLG-235/MOA-2003-BLG-53

Planetary ParametersPlanetary Parameters

• Best-fitting model:Best-fitting model:

• Planet mass: Planet mass: 1.5 Jupiter masses1.5 Jupiter masses

• Star mass: Star mass: 0.36 solar masses0.36 solar masses

• Planet-star distance: Planet-star distance: 3 times Earth-Sun distance3 times Earth-Sun distance

• Distance from Earth: Distance from Earth: 16000 light-years! 16000 light-years!



Space-based transit detectionSpace-based transit detection

HST

MOST

CoRoT

KEPLER

Brown (2001)

1.5%

1.6%tran

sit d

ept h

Na I wavelength (microns)

What’s in their What’s in their atmospheres?atmospheres?

Opaque silicate cloud deck

Extended atmosphereWith gaseous Na, K, H2O, CH4, ...

Line photons blockedhigh in atmosphere

Continuum photonsblocked by clouds

Na I absorption in Na I absorption in HD 209458bHD 209458b

• Charbonneau et al (2002: Charbonneau et al (2002: ApJ 568, 377)ApJ 568, 377)

– Hubble Space telescope / STISHubble Space telescope / STIS

– Weak detection of Na!Weak detection of Na!

– f/f ~ 2x10f/f ~ 2x10–4–4

The amazing evaporating planetThe amazing evaporating planet• Vidal-Madjar et al (2003) Vidal-Madjar et al (2003) NatureNature 422, 123 422, 123

Star occults planetStar occults planet

Spitzer/IRAC 4.5, 8.0 micron

TrES-1: Charbonneau et al. 2005

HD 209458: Deming et al. 2005

0.2 %

Direct detection of infrared light from

planet

-> effective temperature

Water in HD 189733bWater in HD 189733b• Planet silhouette size measured in Planet silhouette size measured in SPITZER/IRACSPITZER/IRAC

3.6, 5.8, 8.0 mm bands during primary transit.3.6, 5.8, 8.0 mm bands during primary transit.

• Wavelength dependence matches water Wavelength dependence matches water transmission spectrum, mixing ratio ~ 5x10transmission spectrum, mixing ratio ~ 5x10–4 –4 ..



Tinetti et al 2007, Nature 448, 163

The continuously habitable zoneThe continuously habitable zone



The Darwin Mission: 2018?The Darwin Mission: 2018?

• Aim: to discover Aim: to discover Earth-like planets Earth-like planets orbiting nearby stars orbiting nearby stars and seek atmospheric and seek atmospheric biosignatures. biosignatures.

• Four interlinked Four interlinked collector mirrors collector mirrors flying ~100m apart.flying ~100m apart.

• Light waves from Light waves from collectors interfere to collectors interfere to cancel out glare of cancel out glare of central star.central star.



You’d look pretty simple from 30 You’d look pretty simple from 30 light-years away toolight-years away too

• Nulling interferometry Nulling interferometry with infrared light from with infrared light from Darwin’s four collectors Darwin’s four collectors eliminates light from star.eliminates light from star.

• Simulated image of our Simulated image of our own solar system seen own solar system seen from 30 light-years away from 30 light-years away detects all inner planets detects all inner planets except Mercury:except Mercury:

Earth

Venus

Mars

(Sun)

Mid-IR spectra of terrestrial planetsMid-IR spectra of terrestrial planets



History of the Earth’s atmosphereHistory of the Earth’s atmosphere

OxygenCarbon Dioxide

Water

Nitrogen

Methane, Ammonia

Time before present (billions of years)

SummarySummary• Transiting hot Jupiters probe:Transiting hot Jupiters probe:

– Interior structureInterior structure

– Formation historyFormation history

– Atmospheric compositionAtmospheric composition

– Albedo and energy budgetAlbedo and energy budget

• Wide but shallow surveys (WASP, HAT, TrES, XO) yielding several Wide but shallow surveys (WASP, HAT, TrES, XO) yielding several planets/year bright enough for transit spectroscopy, planets/year bright enough for transit spectroscopy, Spitzer /JWSTSpitzer /JWST secondary-eclipse studies.secondary-eclipse studies.

• Space-based transit studies capable of detecting hot (CoRoT) and warm Space-based transit studies capable of detecting hot (CoRoT) and warm (KEPLER) super-Earths and determing bulk composition.(KEPLER) super-Earths and determing bulk composition.

• Efficient spectroscopic confirmation essential to eliminate impostors and Efficient spectroscopic confirmation essential to eliminate impostors and determine planet masses.determine planet masses.

• Long-term, high-precision transit timings may reveal lower-mass planets.Long-term, high-precision transit timings may reveal lower-mass planets.

• DARWIN/TPF: nulling interferometry will permit 10-micron spectroscopy of DARWIN/TPF: nulling interferometry will permit 10-micron spectroscopy of terrestrial planet atmospheres.terrestrial planet atmospheres.

Image Credit:NASA/JPL/University of Arizona

Postcards from TitanPostcards from Titan

Transiting extrasolar giant planetsTransiting extrasolar giant planets• 19 examples known.19 examples known.

• Stellar mass and period yield Stellar mass and period yield orbital separation orbital separation a.a.

• Transit shape yields Transit shape yields

– impact parameterimpact parameter

– stellar radiusstellar radius

• Transit depth yields ratio of radiiTransit depth yields ratio of radii

• Hence get Hence get direct measure of direct measure of planetary density.planetary density.

Documents

Andrew Collier Cameron University of St Andrews. Are we alone in the Universe? The plurality of worlds In some worlds there is no Sun and Moon, in others