Extrasolar planets: the Holy Grail of astronomers

Abstract

Are we alone in the Universe? This is a question which divided philosophers as long ago as the age of the ancient Greeks. Epicurus thought that the number of worlds was infinite, while Aristotle believed that the Earth was unique and at the centre of the Universe. Twenty-four centuries of debate and discussion went by before astronomers were able to prove Aristotle wrong! The Earth is not unique, and since 1995 we have known that there also exist planets orbiting stars like the Sun: the extrasolar planets (exoplanets). More than 200 of these worlds are now known, and the number increases monthly. None of these planets really resembles the Earth, but astronomers are sure that exoEarths will be found as soon as appropriate instruments become available.