Prior to the launch of Kepler, ground-based telescopes discovered 3 candidate transiting exoplanets in the field of view of Kepler. But Kepler took a better look and actually verified that one of them is a true exoplanet, named BOKS-1 b (KID-9595827) - a jupiter-sized exoplanet orbiting a G-type star.
In the process of verifying the three candidates, Kepler in turn, discovered that the other two are not exoplanets, but actually Eclipsing Binaries.
The investigators tell the story here. In their own words:
“Three transiting exoplanet candidate stars were discovered in a ground-based photometric survey prior to the launch of NASA’s Kepler mission...All three stars are faint by radial velocity follow-up standard, so we have examined these candidates with regard to eliminating false positives and providing high confidence exoplanet selection.”
“Using the Kepler light curves...we find that two of our candidates are binary stars. The third candidate (BOKS-1) is a...G8V star hosting a newly discovered exoplanet...”
This is what’s so great about Science. Different telescopes could actually check on one another’s results, and verify each other's findings. And so for Kepler, it’s job is not only to discover new planets, but to also verify and confirm true exoplanets.
Direct PDF: http://xxx.lanl.gov/PS_cache/arxiv/pdf/1010/1010.4106v1.pdf