Most exoplanets are discovered by the radial velocity method, (tracking the doppler shifts in the spectrographic lines in the light emitted by the star) but the

Most exoplanets are discovered by the radial velocity method, (tracking the doppler shifts in the spectrographic lines in the light emitted by the star) but the best data is produced by Kepler, which uses occlusion and thus can tell you how big the planet is, by how much the star dims. Both methods are biased towards finding big planets (which produce clear, easy to detect spikes) that are close to their star. (so you get enough data points) Kepler tends to be a little more biased, simply because it hasn't been running long enough: http://en.wikipedia.org/wiki/File:Exoplanet_Period-Mass_Scatter_Discovery_Method_TR.png http://en.wikipedia.org/wiki/File:Exoplanet_Period-Mass_Scat... Kepler was launched in 2009. Realistically, you'd have to run it for another three or four centuries if you wanted to detect exoplanets that orbit as far out as Neptune. (orbital period: 165 years) No wonder we're seeing a lot of planets orbiting close in!