Searching for Exoplanetspauld/Venus/ExoPlanets and Transits.pdf · Advantages of Using Transit...

Searching for ExoplanetsObserving planets as they transit stars

Linda Shore, Exploratorium Teacher Institute

Astronomers are looking for planets that aretransiting stars in our region of the Galaxy

Transit PhotometryIf such a dimming isdetected at regularintervals and lasts a fixedlength of time, then it isvery probable that aplanet is orbiting the starand passing in front of itonce every orbital period.

Advantages of Using Transit Method

• One of the most sensitive methods of detectingsmall planets and those orbiting close to their stars.

• While other methods can determine planetary mass,this method yields the planetary radius.

• Combined with detection methods that yield mass(e.g. radial method), astronomers can estimateplanet’s density.

• By examining light curves of different wavelengthsof light, an absorption spectrum can be constructedwhich will determine composition of the planet’satmosphere.

Disadvantages of Using Transit Method

• Planetary transits are uncommonly observedbecause Earth’s line of sight has to be perfect.

• Transits don’t last long; observation instruments canmiss one in progress.

• Astronomers need to observe a series of transits forthe same planet to confirm that changes inbrightness aren’t caused by other phenomena.

• High rate of “false positives”; binary star systemsproduce similar light curves.

Kepler TelescopeLaunched on

March 6, 2009

Kepler is examiningthe region of the

Galaxy in thedirection of Cygnus,

the Swan…

The KeplerTelescope has100,000 starsavailable tomeasure.

By February2011, Kepler had

alreadydiscovered 1235

planets

The first five planets Kepler discovered

If a planet has been detected by thetransit method, then variations in thetiming of the transit provide an extremelysensitive method capable of detectingadditional planets in the system with sizespotentially as small as the Earth.

Kepler-11 is a sun-like star around which six planets orbit.