The amount of water in the soil and salinity of the oceans may not seem connected, but, in fact, they are both key variables linked to the global water cycle. Variations in soil moisture and ocean salinity are a consequence of the continuous exchange of water between the oceans, the atmosphere and the land Earth’s water cycle, which not only sustains life on Earth but also plays an important role in weather and climate. SMOS, due for launch this 2 November from the russian Cosmodrome of Plesetsk, will be the first satellite mission producing global maps of soil moisture and ocean salinity on a regular basis.