I wanted a planet close in size to Earth. After searching through many candidates, I found one planet close to Earth's mass and with a good location within its solar system. More on that in a bit. First, let's discuss how this planet was discovered.
NASA's Kepler Space Telescope and Mission was designed to discover Earth-size and smaller planets in or near the habitable zone around a star. The Kepler Space Telescope (KST) was launched in 2009 and retired in 2018. During the first four years, the KST was pointed at the same tiny patch of space. Eventually, the primary mission was aborted because of a reaction wheel failure. Reaction wheels are critical in space telescope orientation operations. I have linked to a Youtube video (screened and approved for language and content) below explaining more about a reaction wheel.
Kepler-186 is a system confirmed to have an Earth-size planet, Kepler-186f. Kepler-186f is the first Earth-size planet discovered in the potentially 'habitable zone' around another star, where liquid water could exist on the planet's surface. Kepler-186f is the sixth planet from the star in the Kepler-186 system.
Having a planet closely matching Earth's size and located in the habitable zone made it unique and plausible that life could exist on the planet. Would you have preferred a different planet? If so, what planet would you have chosen for the book?