Final answer:
NASA established three criteria for Kepler's mission to find Earth-like planets to seek potentially habitable worlds capable of supporting life. The criteria are informed by Kepler's laws and observational selection effects. The Kepler mission aimed to estimate the prevalence of such planets in the galaxy.
Step-by-step explanation:
The three criteria for Kepler's mission to find Earth-like planets are based on the detection of planets that are comparable in size to Earth and are situated in the habitable zone of their respective stars. These criteria reflect the conditions considered necessary for life as we know it—namely a rocky planet with potential for liquid water.
NASA devised these specific criteria to focus the search for planets that not only orbit other stars but also have the potential to support life, which is a primary scientific goal in the search for extraterrestrial life.
Kepler's laws of planetary motion were essential in this quest, providing a framework for understanding how planets move around their stars. The use of these laws, derived from Tycho Brahe's meticulous observational data, ensured that the search for exoplanets was grounded in robust scientific principles. Selection effects also play a role, as large and short-period planets are easier to detect than smaller or longer-period ones.
Finally, the Kepler mission contributed significantly to our understanding of how common Earth-like planets might be in our galaxy. Even though the mission observed only a fraction of the Milky Way's stars, the data were extrapolated to estimate the frequency of such planets galaxy-wide.