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How many Earth-sized planets in the TRAPPIST-1 system orbit within the star’s habitable zone?

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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.
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.

In the TRAPPIST-1 system, there are three Earth-sized planets that orbit within the star’s habitable zone.12

The habitable zone is defined as the orbital region around a star where a planet can potentially maintain liquid water on its surface, a condition considered essential for life as we know it. While these three planets are situated within this region, it is important to note that a planet's actual habitability depends on various additional factors, including its atmospheric composition, greenhouse gases, and internal energy sources.1