NASA’s Kepler spacecraft has discovered five new planets orbiting stars beyond the Sun in its first 6 weeks of science observations. The planets — designated Kepler 4b, 5b, 6b, 7b, and 8b — orbit their host stars in periods ranging from 3.2 to 4.9 days. All are significantly larger than Earth and have surface temperatures hotter than molten lava.
The smallest planet, Kepler 4b, is about the size of Neptune. But Kepler 7b is the strangest: It has a density just 17 percent that of water, as light as Styrofoam. Over the next few years, Kepler will find smaller and smaller planets and, in all likelihood, planets similar to Earth in size and temperature.
The five new planets were Monday’s biggest news from Kepler at the 215th meeting of the American Astronomical Society meeting in Washington, D.C., but two other findings deserved more attention than they received.
First, preliminary results indicate the Sun is a fairly normal star. Some astronomers had thought most stars were significantly more active than the Sun, and this activity (flares, for instance) would make any orbiting planets less hospitable to life. Out of 43,000 Sun-like stars in Kepler’s view, however, only one-third are more active than the Sun when it is at solar maximum. Lots of quiescent stars create more regions in the galaxy where life could exist. The quiescent stars also will make it easier for Kepler to find planets like Earth because high activity levels can hide the signatures of low-mass planets.
Second, Kepler found two companion objects that were too hot to be planets (they were hotter than their host stars) but too small to be normal stars. The Kepler team's current thought is that these objects might be abnormally small white dwarfs, weighing perhaps just 15 percent the Sun’s mass. Such objects would be small and hot, but the researchers need more data before they know for sure.