Extrasolar Planets Is there a twin of our Home Planetsomewhere out there? Gero Rupprecht, ESO Brandys,

Giordano Bruno “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) 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 M Jupiter 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: 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? 1. Direct imaging 2. Observation of induced proper motion 3. Variation of the star‘s radial velocity 4. 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" 51 Pegasi only from space: “nulling interferometry” GENIE (ESA/ESO VLTI 2008) DARWIN (ESA) TPF (NASA)

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 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

HARPS: High Accuracy RV Planet Searcher on 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

HARPS: echelle spectrograph, RS= CCD mosaic 4k*4k HARPS inside Echelle spectrum HARPS echelle grating 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 – 1% dip Accessible even for amateurs: Nirölä Obs/Finland Sep 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

All exoplanets known to date --- Earth --- Jupiter 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 planets Li in stellar spectrum! explanation: cannibalism!

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 <<