  Identification of habitable planets beyond our solar system is a key goal of
current and future space missions. Yet habitability depends not only on the
stellar irradiance, but equally on constituent parts of the planetary
atmosphere. Here we show, for the first time, that radiatively active mineral
dust will have a significant impact on the habitability of Earth-like
exoplanets. On tidally-locked planets, dust cools the day-side and warms the
night-side, significantly widening the habitable zone. Independent of orbital
configuration, we suggest that airborne dust can postpone planetary water loss
at the inner edge of the habitable zone, through a feedback involving
decreasing ocean coverage and increased dust loading. The inclusion of dust
significantly obscures key biomarker gases (e.g. ozone, methane) in simulated
transmission spectra, implying an important influence on the interpretation of
observations. We demonstrate that future observational and theoretical studies
of terrestrial exoplanets must consider the effect of dust.
