You might be thinking of the Kepler Space Telescope, which was a NASA mission that discovered thousands of exoplanets (planets outside of our solar system) during its operational lifetime from 2009 to 2018.

The Kepler Space Telescope was named after the German astronomer Johannes Kepler, who was famous for his laws of planetary motion.

It's possible that you heard about a planet named "Kepler" in a science fiction context, but it does not exist in the real world.