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Why is Proxima Centauri b considered a potentially rocky planet in a habitable zone?

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Habitable zone The habitable zones (green) for stars that are like the Sun (middle), hotter than the Sun (top), and cooler than the Sun (bottom). The red areas are those in which liquid surface water would be lost as a result of a runaway greenhouse effect, and the blue areas are those in which liquid surface water would be completely frozen.

Proxima Centauri b is considered a potentially rocky planet because its estimated mass—approximately 17 percent greater than that of Earth—suggests a terrestrial, rocky composition.12

It is classified as being in the habitable zone because it orbits its host star, Proxima Centauri, at a distance where surface temperatures could theoretically allow water to exist in liquid form. Because Proxima Centauri is a small, cool red dwarf star with low luminosity, its habitable zone is located much closer to the star than that of the Sun. Consequently, Proxima Centauri b completes an orbit in just 11.2 days.123

While its location and mass make it a subject of significant interest in astrobiology, scientists note that the planet may be tidally locked and exposed to intense radiation from its host star, which could negatively impact its ability to retain an atmosphere or support life.14