ESO 15/09 - Science Release 21 April 2009 For Immediate Release Lightest exoplanet yet discovered Well-known exoplanet researcher Michel Mayor today announced the discovery of the lightest exoplanet found so far. The planet, “e”, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, plac