Resources: Worksheet, Worksheet (Part 2)

Terminology: Focal Length, Right Ascension, Declination

Tutorials: Importing Images into MaxIm, Photometry in Maxim, Observing Exoplanets

Demonstrations: Habitable Zone, Exoplanet Transit, Velocity Simulator, Doppler Shift with Exoplanet

Exoplanets are not a new concept to astronomy.  With the realization that the Copernican model of the solar system was correct, some scientists began to wonder if other stars were like our sun, and if they too could posses planets. Exoplanets are very faint sources, especially compared to the bright stars that they orbit.  Because of this, most exoplanets are observed indirectly.  There are four primary methods to detecting exoplanets:

The radial velocity method involves watching the spectral lines of a star as a planet orbits the star. Because of the planets gravitational pull on the star, the star will wobble.  This causes Doppler shifts in the spectral lines, allowing astronomers to infer the presence of the planets. This method is most sensitive to massive planets that are located close to their parent star.

Transits are best thought of as miniature eclipses.  When an exoplanet passes in front of its parent star, it blocks some of the light emitted from the star.  Because the planet must be aligned nearly perfectly for us to see the transit.  Most exoplanets can't be detected by transits.  This method, like radial velocity, is most sensitive to planets that are large and close to their parent stars.

In a few exceptional cases, exoplanets have been imaged directly by telescopes.  In order to view the exoplanet, the light from the parent star must be blocked.  Because of glare and the coronagraph that blocks the light from the star, this method can not detect planets that are very close to their parent star.  This method is most sensitive to large planets that are relatively far from their parent star. 

The pulsar timing method was used to make the first detection of extra-solar planets.  It currently holds the record for lowest mass exoplanet discovered (PSR B1257+12 b is comparable in size to Earth's moon.)  Dispite this methods ability to detect very low mass objects, less then 10 planets have been found around pulsars.  This is because most pulsars do not have planets as the supernova that forms the pulsar would destroy any planets that orbited the original star.  Because of this, it is believed that any planets found orbiting pulsar were formed after the supernova occurred.