extrasolar planets is there a twin of our home planetsomewhere out there? gero rupprecht, eso...
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ExtrasolarExtrasolar PlanetsPlanets
Is there a twinIs there a twin
of our Homeof our Home
PlanetPlanet
somewheresomewhere
out there?out there?
Gero Rupprecht, ESOGero Rupprecht, ESO
Brandys, 07.05.2004Brandys, 07.05.2004
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Giordano Bruno1548-1600
“On the Infinite Universe andthe Worlds"
Every major scientific truth passes throughthe following three stages:
1. People say it contradicts the Bible2. People say it is already known3. People say they always knew it right away…
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Michel MayorDidier Queloz(Obs. Geneva)
6.10.1995
Public announcement of the discovery of the first extrasolar planet:
51 Pegasi
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This was one of the most eagerly awaited discoveries - Searches ongoing for decades:
• many teams• many stars• different techniques
Without success!
Why?
• Were the techniques not sensitive enough?• Perhaps there were no planets after all?
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The new planet: a mystery!
• orbital period: 4.2 d• Mass: ~0.5 MJupiter
This is against allthat was expected!
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„Hot Jupiter"circling its star inside the orbit of Mercury
Consequences:• Extreme temperatures• Extreme climate• IF it is a gas planet: very short lifetime!
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New discoveries followed suit
Today (May 2004): 123 Exoplanets known in 108 systems
with 13 multiple planets
The most successful teams:
• Geneva (Mayor, Queloz)• California/Carnegie (Marcy, Butler)• Anglo-Australian Telescope• Pennsylvania State University (Wolszczan)
More teams at different observatories
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Where are they located?
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How can Exoplanets be discovered?
1. Direct imaging2. Observation of induced proper motion3. Variation of the star‘s radial velocity4. Variation of the star‘s brightness:
a.Gravitational lens effectb.Transit!
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Ad 1: Direct imaging of the planet
VERY difficult due to• extreme contrast: about 1:10^9 in the case of Jupiter/Sun at 5pc distance• very small angular separation: <1"
51 Pegasi
• only from space: “nulling interferometry”• GENIE (ESA/ESO VLTI 2008)• DARWIN (ESA)• TPF (NASA)
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Using the effects of gravity
Depending on our relativePosition we see either• a “wobble” in the star’s position or• a “wobble” in the star’s velocity
Period = orbital period of the companion
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Ad 2: Observation of a star‘s proper motion
• Superposition of space and orbital motion.• More difficult with increasing distance and decreasing mass of the planet. • Requires at least observation of one full orbit.• So far no planet discovered but one confirmed by HST• ESO VLTI: 10^-4‘‘ – ok for Jupiter, not Uranus in 10pc• ESA mission GAIA to measure precise PM in 2012
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Ad 3: Variation of the star‘s radial velocity
• Dependent on the mass ratio star/planet• Independent of the distance from the observer• Jupiter causes 13m/s variation, Earth only 0.1m/s• Measurement limit 1m/s (HARPS at ESO 3.6m)
Geneva team
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HARPS: High Accuracy RV Planet Searcheron ESO/La Silla 3.6m All you need is … Stability!
• Coude focus• fibre fed• image scrambler• no focusing mechanism• climatized room• vacuum vessel• heating blanket• special calibration method
• long-term stability: 1m/s• short-term: ~30cm/s• good for Uranus-like planets
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HARPS: echelle spectrograph, RS=120000 CCD mosaic 4k*4k
HARPS inside
Echelle spectrum
HARPS echellegrating
Cross dispersed
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Ad 4a: Gravitational lens effect
Very recent: published in April 2004
Observation Interpretation
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Ad 4b: Variation in brightness due to a transit
One case known:
HD 209458 – 1% dip
Accessible even for amateurs:
Nirölä Obs/FinlandSep. 2000
Meade 16’’+ Focal reducerSBIG ST7E CCD
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Transit method applied by HST
Precise photometry
Detection of aNa “atmosphere”
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Transit method: the future• only for a short fraction of the orbital period (hours)• only if Earth is nearly exactly in the orbital plane• Jupiter: 1% dimming, but Earth: 0.01% dimming!
Currently the only method to discover Earth sized planets: only from space!• COROT (ESA, >2006; 30cm telescope)
• Kepler (NASA, >2007; 95cm telescope, differential photometer)
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Some examples for exoplanet systems
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All exoplanetsknown to date
--- Eart
h
--- Ju
pit
er
For comparison:Our solar system
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Exoplanets – what do we know about them?
Obviously: they are clearly different from our own system! But who is typical: we or them?
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Multiple planetsRadial velocity curveshows 2 periods
Their orbits comparedto Earth’s orbit
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A strange case: cannibal star – detected by VLT!
HD 82943• 2 planets• Li in stellar spectrum!
explanation: cannibalism!
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Exoplanet summary
• a new, “hot” field in astronomy• within reach of amateurs!• appealing for the general public• large potential for exciting discoveries
>> Europe in the lead <<