Thirty Billion Planets in the Milky Way

On this photo you see, from right to left, noted astronomy popularizer Donald Goldsmith, leading SETI scientist Jill Tarter, planet hunter Geoff Marcy, and Geoff's wife, chemist Susan Kegley. I took this snapshot last evening, at a banquet sponsored by the Astronomical Society of the Pacific (where I was tickled to be one of the honorees). Dr. Marcy (of the University of California, Berkeley, who is arguably the leading discoverer of planets in the world) spoke about the ongoing hunt for planets with the Kepler spacecraft. He and the mission team have more reason for optimism than ever, it appears. Based on the first two years of Kepler investigation, they think there might be some 30 billion planetary systems in the Milky Way Galaxy. He called it a "tsunami of planets" in the Kepler data. 

Many of the Kepler stars have more than one planet (just like the Sun does.) A star they call Kepler 11 has six planets and they are "co-planar" -- meaning if you pass a sheet of paper through their orbits, all six planets lie in the same sheet of paper. This indicates that the system of planets formed from a flattened doughnut of a "mother cloud", just like our own solar system did. 

And most exciting, as the Kepler teams finds and examines more and more planet candidates, they are finding that SMALLER planets are more common than bigger ones. So, while earlier techniques, that were better at finding big planets like Jupiter, found many Jupiters out there, now (with Kepler) it is becoming clear that smaller planets may make up a greater fraction of the planets in our Galaxy. Since we think smaller planets are probably better candidates for the kind of life that builds computers and does Facebook, this is good news for those who would like a universe in which we humans are not the only intelligent species.