The Kepler spacecraft was designed to investigate humanity's last unexplored frontier: the far reaches of space. The NASA space telescope looks deep into the Milky Way galaxy for signs of habitable planets where humans could potentially thrive. Of the thousands of planets it has identified, three are in livable orbits similar to Earth's. The planet most similar to Earth is Kepler-186f, known as "Earth's cousin." Over 490 light years away, all that NASA knows is that Kepler-186f's size and distance from its star are comparable to Earth's. As technology advances, hopefully we will learn more about Kepler-186f's ability to nurture life. Perhaps someday our descendants will cross the insurmountable distance to explore the surface of Earth's cousin, maybe even make contact with life on another world. Which of the following best describes the main idea of the second paragraph?