Somewhat more than 4000 planets orbiting stars outside our solar system are known so far. Of these so-called exoplanets, about 96 percent are significantly larger than our Earth, most of them more comparable with the dimensions of the gas giants Neptune or Jupiter. This percentage likely does not reflect the real conditions in space, however, since small planets are much harder to track down than big ones. Moreover, small worlds are fascinating targets in the search for Earth-like, potentially habitable planets outside the solar system.
The 18 newly discovered worlds fall into the category of Earth-sized planets. The smallest of them is only 69 percent of the size of the Earth; the largest is barely more than twice the Earth's radius. And they have another thing in common: all 18 planets could not be detected in the data from the Kepler Space Telescope so far. Common search algorithms were not sensitive enough.To read more, click here.