Exoplanets Revisited


Cassel Sloan


Presented at the Astronomy Club of Augusta meeting

at Augusta State University 

on July 20, 2007



I.  What are Exoplanets?

•      Exoplanets are planets that have been found around stars other than the sun.

•      There are currently 246 exoplanets around 210 stars known. That compares to the 161 exoplanets around 137 stars known last time (2005 July).


II. Ways to find exoplanets

•      Pulsar timing

•      Astrometry

•      Radial velocity

•      Gravitation microlensing

•      Transit method

•      Circumstellar disks

•      Direct observation


Pulsar timing

•      Pulsar timing uses anomaly in timing in the pulsing of pulsars to find companions

•      This method was the first to find planets.



•      Astrometry tries to detect an occolation in the proper motion of a star.

•      Astrometry is the first method used to try to find planets.

•      Due to limitations of current equipment, no planets have been found by astrometry.


Radial velocity

•      Radial velocity uses the Doppler effect to look for a planet’s pull on a star.

•      This method is the one that has found the most planets.


Gravitational microlensing

•      Gravitational microlensing uses gravity’s affect on light to find planets.

•      Gravitational microlensing main advantage is that it can detect Earth sized planets, however it only happens by chance and can not be repeated.


Transit method

•      The transit method uses the dimming of star by planets going in front of it.



Circumstellar disks

•      Circumstellar disks are dust clouds around a star which a planet can distort.

•      This method requires space telescopes since the atmosphere absorbs most of the light from the dust clouds.


Direct observation

•      Direct observation tries to see a planet directly.

•      The stars light usually far outshines the planet.

•      There have been four planets found by this method.

•      Brown dwarf & planet



III. New discoveries

•      Confirmed microlensing planets

•      COROT-found planets

•      HD 209458 b and HD 189733b spectra

•      Gliese 581 c and d


Confirmed microlensing planets

•      There are now four planets that have been confirmed.

•      OGLE235-MOA53 b

•      OGLE-05-071L b

•      OGLE-05-169L b

•      OGLE-05-390L b


COROT found planets

•      The new Convection Rotation and planetary Transits (COROT) project has found its first planet.

•      • It is called Corot-exo-1b


HD 209458 b and HD 189733b spectra

•      HD 209458 b and HD 189733b are the first two exoplanets spectra examined for water.

•      A study HD 209458 b did not find water.

•      New research says that HD 189733b may have water and the study of HD 209458 b may be wrong.


Gliese 581 c and d

•      Planets in the Goldilocks zone may have liquid water.

•      Scientists looking to see what kind of planets they are




•      More planets

•      WATER

•      Maybe LIFE!