no star systems have been discovered with planets so large that they have moons the size of Earth. The largest known moons in our own solar system, such as Ganymede and Titan, are substantial in size but significantly smaller than Earth. Discovering a moon with the size and conditions necessary for habitability would be a significant scientific finding.
However, it is important to note that our understanding of exoplanets (planets outside our solar system) is constantly evolving, and new discoveries are being made regularly. As observational techniques improve and new missions are launched, it is possible that we may find star systems with large planets hosting moon-like objects in the future.
Regarding the habitability of such moons, several factors come into play. For a moon to be habitable, it would generally require a stable atmosphere, a suitable distance from its host planet to maintain conditions for liquid water, and a range of other factors conducive to life as we understand it. Additionally, the moon's host planet would need to be within the habitable zone of its star, where conditions are favorable for the existence of liquid water on the planet's surface.
While it is intriguing to consider the potential habitability of such large moons, much remains unknown about the possibilities and conditions necessary for life beyond Earth. Future advancements in astronomical observations and space exploration may provide us with more insights into the diversity and habitability of celestial bodies in our universe.