Geoff Marcy

Geoff Marcy, astronomer and planet hunter at UC- Berkeley, in an interview on SPACE.com, says that several tens of thousands of exoplanets will likely be discovered in the next few decades, largely because of the capabilities of NASA's Kepler planet-hunting spacecraft, and because of the even greater capacities of follow up probes already on the way.

He said Earth-like planets will be found, but Earth-like planets in the habitable zone of their parent stars-- which would mean they could support life as we know it-- are likely to be rare. Marcy points out that worlds the size of Earth would be lightweights in systems that contain Jupiter-sized and larger worlds, and the smaller world could easily get ejected from the system if it came too close to the big guys.

He also suggested intelligent beings and technological civilizations may be rare, citing the fact that such intelligence has arisen on Earth only once, and that one instance occurred extremely recently in geologic time.

That view notwithstanding, Marcy also called for an "Apollo-style" SETI program that would conduct a thorough, systematic search for alien signals, finally really testing the premise underlying SETI after all these years.