Earthanalog

An Earth analog, or Earth-analog, is a planetary body whose properties resemble Earth’s in ways relevant to habitability and exploration. In exoplanet science the term commonly refers to rocky planets with radii and masses not far from Earth’s and that orbit in or near the habitable zone of their star, where liquid water could exist on the surface. The definition is not strict; terms such as Earth-sized, Earth-like, or terrestrial are often used as approximate qualifiers. A true Earth twin would closely match Earth in mass, radius, composition, atmosphere, and orbital configuration, and no such world has been confirmed.

Assessing Earth analogs relies on methods such as transit photometry and radial-velocity measurements to estimate size and mass, along with spectroscopic observations to probe atmospheres. Characterizing atmospheres and surfaces is challenging with current technology, and many candidate worlds remain only partially characterized or hypothetical.

Significance: Earth analogs help scientists study planetary formation, atmospheric evolution, and the potentially habitable conditions outside the Solar System. The habitable zone concept guides the search, but actual habitability depends on additional factors including atmospheric composition, greenhouse effects, geology, magnetic fields, and stellar activity.

Examples: Several well-known exoplanets, such as Kepler-186f, Kepler-62f, and some TRAPPIST-1 planets in or near the habitable zone, are discussed as Earth-analog candidates, though none has a confirmed Earth-like atmosphere or surface conditions.

In brief, Earth analog is a provisional category used to describe worlds that resemble Earth in aspects relevant to habitability, guiding ongoing observational campaigns.