Final answer:
The Kepler mission was a space telescope launched by NASA to search for exoplanets by detecting transits across stars. It discovered thousands of exoplanets before technical issues ended the primary mission in 2013, and it is now succeeded by the TESS mission.
Step-by-step explanation:
The correct statement explaining what the Kepler mission was is option b): The Kepler mission was a space telescope that searched for exoplanets. Launched in 2009 by NASA, the Kepler space telescope had the dedicated task of discovering transiting exoplanets by monitoring the brightness of over 150,000 stars in the region of the constellation Cygnus. The mission's groundbreaking work has led to the discovery of thousands of exoplanets, including many that are potentially earthlike, by detecting minute changes in the brightness of stars when planets transit in front of them.
Despite technical issues with its reaction wheels, which ended its primary mission in 2013, Kepler continued to collect valuable data for an additional two years. The mission was pivotal in increasing our understanding of the frequency of exoplanetary systems and contributing to the field of astronomy, particularly in the study of extrasolar worlds.
Kepler's legacy continues with new missions like TESS, which seeks to expand the search for exoplanets to include brighter, nearer stars across the entire sky.