TRAPPIST-1d

TRAPPIST-1d is a small exoplanet (about 40 percent the mass of the Earth), which orbits on the inner edge of the habitable zone of the ultra-cool red dwarf star TRAPPIST-1, located 40.7 light-years (12.5 parsecs) away from Earth in the constellation of Aquarius. The exoplanet was found by using the transit method. The first signs of the planet were announced in 2016, but it was not until the following years that more information concerning the probable nature of the planet was obtained. TRAPPIST-1d is the second-least massive planet of the system. It receives just 4.3% more sunlight than Earth, placing it on the inner edge of the habitable zone. A 2025 study, based on a James Webb Space Telescope observation, found that the data was "satisfactorily" consistent with TRAPPIST-1d having no atmosphere at all. Nevertheless, there is still a "marginal possibility" the planet has an atmosphere, but determining this with greater confidence would require a different detection technique.