Transcript Extrasolar Planets

Extrasolar Planets
Is there a twin
of our Home
Planet
somewhere
out there?
Gero Rupprecht, ESO
Brandys, 07.05.2004
Giordano Bruno
1548-1600
“On the Infinite
Universe and
the Worlds"
Every major scientific truth passes through
the following three stages:
1. People say it contradicts the Bible
2. People say it is already known
3. People say they always knew it right away…
Michel Mayor
Didier Queloz
(Obs. Geneva)
6.10.1995
Public announcement of
the discovery of the
first extrasolar planet:
51 Pegasi
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?
The new planet: a mystery!
• orbital period: 4.2 d
• Mass: ~0.5 MJupiter
This is against all
that was expected!
„Hot Jupiter"
circling its star inside the orbit of Mercury
Consequences:
• Extreme temperatures
• Extreme climate
• IF it is a gas planet: very short lifetime!
New discoveries followed suit
Today (May 2004): 123 Exoplanets known
in 108 systems
with 13 multiple planets
The most successful teams:
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Geneva (Mayor, Queloz)
California/Carnegie (Marcy, Butler)
Anglo-Australian Telescope
Pennsylvania State University (Wolszczan)
More teams at different observatories
Where are they located?
How can Exoplanets be discovered?
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Direct imaging
Observation of induced proper motion
Variation of the star‘s radial velocity
Variation of the star‘s brightness:
a. Gravitational lens effect
b. Transit!
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"
• only from space:
“nulling interferometry”
• GENIE (ESA/ESO VLTI 2008)
• DARWIN (ESA)
• TPF (NASA)
51 Pegasi
Using the effects of gravity
Depending on our relative
Position we see either
• a “wobble” in the
star’s position or
• a “wobble” in the
star’s velocity
Period = orbital period of the companion
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
Ad 3: Variation of the star‘s radial velocity
Geneva team
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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)
HARPS: High Accuracy RV Planet Searcher
on ESO/La Silla 3.6m
All you need is … Stability!
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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
HARPS: echelle spectrograph, RS=120000
CCD mosaic 4k*4k
HARPS inside
HARPS echelle
grating
Echelle spectrum
Cross dispersed
Ad 4a: Gravitational lens effect
Very recent: published in April 2004
Observation
Interpretation
Ad 4b: Variation in brightness due to a transit
One case known:
HD 209458 – 1% dip
Accessible even for amateurs:
Nirölä Obs/Finland
Sep. 2000
Meade 16’’
+ Focal reducer
SBIG ST7E CCD
Transit method applied by HST
Precise photometry
Detection of a
Na “atmosphere”
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)
Some examples for exoplanet systems
Earth
Jupiter
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All exoplanets
known to date
For comparison:
Our solar system
Exoplanets – what do we know about them?
Obviously: they are clearly different from our own system!
But who is typical: we or them?
Multiple planets
Radial velocity curve
shows 2 periods
Their orbits compared
to Earth’s orbit
A strange case: cannibal star – detected by VLT!
HD 82943
• 2 planets
• Li in stellar spectrum!
explanation: cannibalism!
Exoplanet summary
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a new, “hot” field in astronomy
within reach of amateurs!
appealing for the general public
large potential for exciting
discoveries
>> Europe in the lead <<