Several techniques have been developed:
- The first technique is to look for a very slight drop in the light from a star when the exoplanet crosses in front of the star; this is like an eclipse, but usually called a transit.
- Another technique is to look for a very small change in the star’s spectra from blueshift to redshift back, and repeated as the planet revolves around the star and tugs it very slightly back and forth due to the gravitational pull.
- Another technique is somewhat related to the Doppler blueshift to redshift, where a slight wobble in the star’s position is actually observed.
- Another interesting technique is called gravitational lensing, where one object ‘lenses’ the image of a second object around it.
Technology has allowed both amateur and professional astronomers the ability to make such observations from here on Earth. And eventually technology should allow astronomers to directly view exoplanets.
The Discovery of Extrasolar Planets
So what has been discovered to date?
As of fall 2014, astronomers have found 1,822 planets in 1,137 planetary systems and 467 multiple planet systems. Seven planets have been discovered around the star HD10180, the largest known system outside our solar system. And currently there are thousands of candidate exoplanets.
So what are these exoplanets like?
Most are much bigger than Earth, more like Jupiter and even much larger than Jupiter. Many are extremely hot; they orbit quite close to their star or stars. And many of these will “lose” to their parent stars and crash into their star as the star’s gravity pulls them in.