Planet-hunter Geoff Marcy is quoted in this story in The Oklahoman on the prevalence of planetary systems around other stars. His estimate: 20 billion systems in the Milky Way alone, and that’s the lower end of the range. In fact, fully half of the galaxy’s 200 billion stars may be capable of supporting planets.

From the article:

Marcy said astronomers may spot a rocky Earth-like planet as soon as five years from now, but will have to hypothesize about its life-sustaining possibilities until a robotic probe can be sent to the extrasolar planetary system.

Exactly so, at least for close-up studies, but missions like Terrestrial Planet Finder may be able to analyze planetary atmospheres closely enough to find the methane and ozone signature of life. We’ll need those missions (along with the earlier Kepler and Space Interferometry Mission projects) to help us choose our first targets for interstellar probes. Given the magnitude of the enterprise, we’ll want our destination star to be orbited by a world with plenty of water and an atmosphere that holds out the promise of an ecosystem.

How do you do high-resolution spectroscopy on distant worlds? One of many problems is that an Earth-sized planet would be out-shone by its star by a factor of a billion to one. An elegant solution is New Worlds Observer, pioneered by University of Colorado at Boulder astronomer Webster Cash. If the name sounds familiar, it’s because of Cash’s work on MAXIM — the Microarcsecond X-ray Imaging Mission — which will be used to achieve images of black holes with 1 million times the resolution of Hubble. The Phase II study Cash did for NASA’s Institute for Advanced Concepts is called “”X-Ray Interferometry: Ultimate Astronomical Imaging,” and is available at the NIAC site.

New Worlds Observer would be equally stunning. Think of a space-based pinhole camera, with an occulting shield hundreds of meters in diameter; the ‘camera’ is monitored by a space telescope flying in the shield’s focal plane. A marker page for the remarkable New Worlds Observer concept can be found here. Watch as this idea develops; later generations of the concept could supply us with breathtaking close-ups of extrasolar planets. Cash told me last year that such a system scales nicely. Using up to fifty sets of spacecraft and interferometry techniques, images duplicating the view of an extrasolar planet from 100 kilometers would not be out of the question.