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A revolution has occurred in the last two decades in the world of astrophysics.   It all started in the early '90s with the first discovery of 'new worlds' around other stars. The word 'Extrasolar planet' (or Exoplanet) is now widely used to identify planets\footnote{A planet is a celestial body massive enough to be bounded by its self gravity (unlike a rock or an asteroid, that are kept together by electromagnetic forces), but not massive enough to produce energy through nuclear fusion (as stars do)} orbiting a star other than the Sun.  Different methods for capturing the elusive signature of these distant worlds have been used, leading to the discovery of thousands of exoplanets. However the most remarkable discoveries came only in the last couple of years thanks to the KEPLER space telescope. This amazing instrument has been patiently looking for the tiny dimming induced by the passage of a planet in front of its host star, and helped todefinitively  answer two fundamental questions: \begin{enumerate}  \item How common are planets?  \item How common are planets similar to Earth?