But the coolest thing about Kepler is that it's broken – and has been since 2013, just four years after its mission began. Kepler used three of its reaction wheels to keep it centered precisely on its target, and one of them failed. Without it, the spacecraft was unstable, and any outside force could knock it totally out of position.
Instead of calling it quits, the mission scientists transitioned into a second wave of observation called K2, which started in 2014. K2 uses the power of the sun to keep Kepler from being unwieldy. The light from the sun acts as a virtual third reaction wheel, physically pushing against the craft's solar panels as the three physical reaction wheels push back. The tension keeps the telescope in place, but it has to be repositioned every 80 days to keep the solar forces hitting it in just the right place.
It's an ingenious fix, to say the least – but one that dramatically changed the way Kepler could operate, the stars it could look at, and how long it could investigate them. So it's incredibly exciting that K2 has been so successful, resulting in over 100 confirmed exoplanets so far and bringing in droves of candidates to investigate.