Les techniques de détection directe

Exoplanètes,–,Les,techniques,de,détec6on,directe,
Exoplanets+–+direct+detec1on+techniques++
Technique,du,transit,/,Transit,method,,
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!
A! semi-direct! technique! consists! to! detect! the! shadow! of! an! exoplanet.! The! brightness! of! a! star! decreases!
periodically!when!an!exoplanet,!seen!from!Earth,!masks!a!part!of!the!stellar!disk.!Photometric!measurements!allow!
to! determine! the! frac@on! of! blocked! flux! and! then! to! es@mate! the! surface! of! the! transi@ng! exoplanet.! By!
combining! this! technique! with! the! radial! velocity,! radius,! mass,! and! therefore! the! exoplanet! density! can! be!
measured.!The!bulk!density!provides!informa@on!on!the!internal!structure!and!composi@on!of!extrasolar!planets:!
rocky,!ice!or!gaseous.!
Technique,d’imagerie,directe,/,Direct+imaging+method++
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!
Direct!imaging!of!exoplanets!is!facing!two!challenges:!a!@ny!angular!separa@on!on!the!
sky! between! the! star! and! its! planet,! and! a! contrast! in! brightness! greater! than! one!
million.! Modern! techniques! of! adap@ve! op@cs! and! coronagraph! have! permiGed! to!
achieve!the!first!picture!of!massive!exoplanets!with!large!orbital!distance.!
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!
The!characteriza@on!of!exoplanets!atmosphere!can!be!performed!by!comparing!the!spectrum!from!the!star!during!the!transit!of!the!planet!and!when!the!planet!is!
out!of!the!stellar!disk!(transmission!spectroscopy).!Another!approach!consists!to!analyze!the!thermal!spectrum!(in!infrared)!of!the!planet!when!it!disappears!behind!
the!star!(an@-transit).!Finally!when!the!planet!is!angularly!resolved,!it!is!possible!to!directly!analyze!its!thermal!emission!spectrum!to!iden@fy!the!components!of!its!
atmosphere.!
Exoplanètes,–,Caractérisa6on,des,atmosphères,,
Exoplanets+–+atmosphere+caracterisa1on+