The Universe is such a vast place that it is beyond the capability of mankind to understand it’s true extent. The fact that there are on the order of 100 billion galaxies out there, each containing close to 100 billion stars is a mindboggling thought. Our star, the Sun, has 8 planets that orbit around it. This observation has naturally lead mankind to wonder how many other stars out there in the vast universe might also have planets orbiting around them. Although a relatively old question, it was not until 1995 (Mayor & Queloz 1995) that astronomers first discovered evidence of a new planet outside of our solar system. Since then astronomers have discovered 519 other planets (January 2011)*. These planets outside our solar system, referred to as extra-solar planets or in short exoplanets, have been detected using many different methods. One of the main techniques, which will be covered in this literary review, is the transit method.

Exoplanet discoveries by the transit method

The transit method is only one of  the methods of discovering an exoplanet. In the figure below some of the most common methods are shown indicating how many exoplanet candidates each method has detected.

The exoplanet detection tree shows some of the most common methods for exoplanet detection and how many planets each method has detected. Totalling the number of detected planets by each method gives 612, a value greater than 505 because often multiple methods can detect the same exoplanet.

When close-in exoplanets pass in front of their host star a portion of the light from the star is blocked out and a decrease in the photon flux is measured. These planets are known as transiting exoplanets. Measuring the photon flux over time allows astronomers to make a light curve. It is this light curve with it’s characteristic shape and depth which lets astronomers characterise the exoplanet and in some cases its atmosphere. It is truly remarkable that from observations of an unresolved point of light astronomers are able to infer precise values for the properties of the star-planet system.

* exoplanet.eu