Physically TRAPPIST-1 h is the smallest and least massive of the planets in its system. Most of these planets approach or exceed Earth'smass, but TRAPPIST-1 h has only a third of the mass of Earth. Its diameter is some 78% that of Earth, showing that it must be considerably less dense (for reasons that are not clearly understood, but may reflect the compounds that make it up, or possibly its internal physical structure).
Because the reddwarfTRAPPIST-1 is comparatively cool by stellar standards, its habitable zone (the zone in which the heat provided by the star is suitable for liquid water to exist) is a narrow region very close to the star. Despite its close orbit, however, TRAPPIST-1 h lies beyond the outer fringes of this zone. This means that (unless unforeseen effects are active on the planet) its temperature will be an estimated -100°C, and its surface is therefore likely to be covered in ice.