According to NASA, the mission is as follows:
The scientific objective of the Kepler Mission is to explore the structure and diversity of planetary systems. This is achieved by surveying a large sample of stars to:
- Determine the percentage of terrestrial and larger planets there are in or near the habitable zone of a wide variety of stars;
- Determine the distribution of sizes and shapes of the orbits of these planets;
- Estimate how many planets there are in multiple-star systems;
- Determine the variety of orbit sizes and planet reflectivities, sizes, masses and densities of short-period giant planets;
- Identify additional members of each discovered planetary system using other techniques; and
- Determine the properties of those stars that harbor planetary systems.