TRAPPIST-1d, also designated as 2MASS J23062928-0502285 d, is an exoplanet, likely rocky, possibly orbiting within the habitable zone around the ultracool dwarf star TRAPPIST-1 approximately 40 light-years (12.1 parsecs, or nearly 3.7336×1014 km) away from Earth in the constellation of Aquarius. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

{:height="360px" width="360px"}{: .align-left}

TRAPPIST-1d is a terrestrial exoplanet with a radius of approximately 0.772 R⊕, intermediate in size between Mars (with a radius about half that of Earth) and Earth.[4] The mass has been estimated to be around 0.41 M⊕. These values allow its standard gravity to be estimated as 6.79 m/s² (69% of Earth value). With these numbers one can calculate a density of 4.95 g/cm^3. It has an equilibrium temperature of 288 K (15 °C; 59 °F).