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An Earth analog (or simply an Earth, and another name is exo-Earth or exoearth) is an extra-solar planet that shares characteristics of Earth. Characteristics of interest include similar radius, mass, constituency, atmosphere, habitability, and host star type (e.g., main-sequence G-type star): a planet with every one of these characteristics would be of considerable interest, but as of 2022, the term is used more loosely due to the few candidates that have been found; for example, it would likely be used for a rocky planet of mass within a factor of two of Earth's that is within a host star's habitable zone. I think it is safe to say "extra-solar" because people hope for something more like Earth than Venus or Mars, which are the best examples within the solar system.