But the similarities end there. Both of the newfound planets reside in tight orbits around their parent star that ought to drive their surface temperatures to life-unfriendly extremes. Torres and his colleagues estimate that Kepler 20 f, the cooler of the two, has a temperature in the neighborhood of 430 degrees Celsius—hot enough to melt lead. "These are definitely too hot to be habitable, at least too hot to support life as we know it," he says.
In a separate study submitted to the Astrophysical Journal, the Kepler group reports finding three other small planets orbiting the same star, ranging from about two to three times the diameter of Earth. All five planets around Kepler 20 rank among the smallest-diameter planets discovered to date. (Astronomers have been able to measure the physical dimensions of only about 200 exoplanets to date; the diameters of another 500 or so planets are unknown.)
The Kepler 20 system has a very different architecture than does our solar system. For starters, all five worlds orbit closer to their host star than Mercury, the innermost planet in our solar system, orbits the sun. And unlike our solar system, where the inner planets are terrestrial worlds and the outer planets are gas giants, the Kepler 20 system is not neatly divided. "This system has gas worlds and rocky worlds," Torres says. "But they're all mixed up; they're not separated like in our own solar system. This is a very interesting thing that we have never seen before."