Today, a ground-breaking discovery was announced by Michel Mayor: A 1.9 Earth mass exoplanet has been found. It's name is Gliese 581 e, located only 20.5 light-years away in the constellation Libra (“the Scales”). Gliese 581 e is the lightest known exoplanet to date. Among the 346 exoplanets known so far, it is the most similar to earth in terms of mass.
It has a period of 3.15 days, it lies very close to it's host star and orbiting so fast that a full year on that planet takes only 3 earth-days.
It is most likely a rocky planet, says Xavier Bonfils. If that is true, Gliese 581 e may have hills and mountains similar to Earth. And you could probably walk on it's surface but you'd weigh almost twice heavier, so you won't get very far. And because it orbits so close to it's parent star (at 0.03 AU) it probably won't have any atmosphere or air to breathe, and it's surface is probably scorchingly hot. Obviously it's not within the Habitable Zone of the Gliese star system.
Not to be taken lightly, the discovery of the lightest exoplanet just twice the mass of earth is a tremendous progress in just 14 years. It provides a big hint of what is to come soon: The discovery of a truly earth-like planet within the Habitable Zone.
Links: ESO Press Release