NASA's Kepler mission finally began to release data on some of its candidate planet-hosting stars. In a bit of controversial, but to some extent understandable maneuvering, the Kepler team has kept what are probably the juiciest systems to themselves. The New York Times had an excellent piece on this tale. Regardless of what data any of us get our sticky paws on there is still a big hurdle to deal with. Kepler is seeking the tiny dips in starlight when planets transit their stellar hosts, but this alone is not enough to either confirm with absolute certainty the presence of a planet, or to determine the mass and detailed orbital characteristics of new worlds. The next stage involves painstaking followup with ground-based telescopes equipped with exquisite spectrometers, seeking the wispy signs of Doppler shifting starlight due to the gravitational offsets induced by planets.
It's quite a bottleneck. It's also pushing the limits of experimental sensitivity as we seek planets equivalent to the Earth - where the stellar 'wobble' can be mere centimeters per second, the speed of a royal wave. Kepler hasn't even got to those candidates yet, with orbits close to 12 months in length we need the next several years to witness multiple transits. There is no doubt that it will take a great amount of scientific cooperation and effort to finally nail down the number of Earth-equivalent worlds that Kepler sees.
Even then, what we'll end up with is really just (although 'just' is relative) a well defined estimate of how many such planets should exist galaxy-wide - together with some idea of their typical compositions and orbits. Bottom line is that the newspaper banner in three or four years will read something like '15 %' - this being the fraction of normal stars hosting small rocky worlds. Is that worth the $600 million for Kepler, plus many more millions for all the followup work ? Such is the nature of modern fundamental science. The Large Hadron Collider costs well in excess of $6 billion, that's about a billion per physics question that it might help answer. The overall cost of the Human Genome Project was about $3 billion - roughly a dollar a base-pair.
I'd argue that by comparison Kepler is positively efficient, but it does raise an interesting question. Just how much are we as a species willing to invest in the search to find other worlds and to seek out signs of other life in the universe ? It's not a cheap enterprise. For me though it is no less important than understanding fundamental physics, or our genetic blueprints. In fact I'd stick my neck out and suggest that unless we find new worlds, new biospheres, we will never have a way to place the Earth and ourselves in proper scientific context. The answer to our origins will come from seeing the bigger picture, and that is surely cheap at any price.