For its first billion or so years, Mars was partly covered in water, as dry ocean basins and riverbeds on its surface now attest. But three billion years ago the planet lost its magnetic field, possibly due to a cooling of its core, allowing the solar wind to strip away its atmosphere. This, so the thinking went, caused the water to evaporate into space.
However, according to a new study, it appears that the water may still be there, trapped in the pores of volcanic rock.
