Binary terrestrial planets have been theorized to exist, in which two terrestrial planets orbit a common center of mass. While there are no confirmed binary terrestrial planets in our own solar system, the Kepler space telescope has discovered several such systems in other star systems.

The likelihood of binary terrestrial planets forming depends on various factors, including the protoplanetary disk conditions and the dynamics of planet formation. In general, it is considered less common for terrestrial planets to form in close orbits around each other, as their gravitational interactions can destabilize their orbits or lead to collisions and mergers. However, under specific conditions, binary terrestrial planets may form, such as through gravitational instabilities or planetesimal accretion.

The existence of binary terrestrial planets can have implications for planetary habitability and the potential for life beyond Earth. Some studies have suggested that the gravitational interactions between binary planets could influence their climate stability, tidal heating, and the ability to sustain liquid water on their surfaces. Binary planets may also affect the formation and evolution of moons, potentially providing additional habitable environments.

Overall, while binary terrestrial planets are not as common as single terrestrial planets, their existence is theoretically possible and has been observed in other star systems. The study of binary terrestrial planets expands our understanding of planetary system formation and the diversity of planetary configurations in the universe.