1. It has been staring at the same (approx) 200,000 stars for its entire mission, looking for a slight and regular dimming by an eclipse of a planet which may only dim the star by a tiny fraction.
2. These stars are generally far, far away, certainly none are close to us.
3. Only a small percentage of these star systems will have an alignment such that planets orbiting the star so that such a little eclipse is possible from Kepler's viewpoint. Only those planetary systems are detectable by Kepler.
4. To find a perfect Earth analog (same mass star, same diameter planet, and same distance from star) it would take at least three transits (more than three years) to put it Kepler's possibles data base.
5. There is a selection bias with this method. Kepler can much more easily find large planets, and/or those close to their stars. The former block proportionally more of their host star's light and thus are more easily detected. The latter do the same, plus have shorter orbital periods so that more stellar transits can be observed which leaves less doubt in the measurements.
The Kepler space telescope has sadly failed, so its primary mission is now over. But it has many hundreds of putative planets in its data ready to be verified by other observations. (It's that damn science peer review thing. If only astronomy was like alternative medicine, astronomers could release the findings now. Alas, astronomy requires confirmation.)
I find it sad that Kepler lost two of its reaction wheels and can no longer point accurately. But the ground laid by Kepler will be fertile for future searches. And then there is all those many hundreds of unverified candidates.
Kepler Mission
R&K
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