A dry Venusian interior constrained by atmospheric chemistry

Venus’s climatic history provides powerful constraints on the location of the inner edge of the liquid-water habitable zone. However, two very different histories of water on Venus have been proposed: one where Venus had a temperate climate for billions of years with surface liquid water and the other where a hot early Venus was never able to condense surface liquid water. Here we offer a constraint on Venus’s climate history by inferring the water content of its interior. By calculating the present rate of atmospheric destruction of H₂O, CO₂ and OCS, which must be restored by volcanism to maintain atmospheric stability, we show that Venus’s interior is dry. Venusian volcanic gases have at most a 6% water mole fraction, which is substantially drier than terrestrial magmas degassed at similar conditions. The dry interior is consistent with Venus ending its magma ocean epoch desiccated and thereafter having had a long-lived dry surface. Volcanic resupply to Venus’s atmosphere, therefore, indicates that the planet has never been liquid-water habitable.