It was already known that liquid water can exist on about half of Mars, though in a very narrow temperature range (around 0C).<p>The green and blue bits have the adequate pressures for liquid water to exist:<p><a href="https://upload.wikimedia.org/wikipedia/commons/2/2c/Mars_topography_%28MOLA_dataset%29_with_poles_HiRes.jpg" rel="nofollow">https://upload.wikimedia.org/wikipedia/commons/2/2c/Mars_top...</a><p>Very narrow phase-space in which liquid water can exist, the yellow rectangle is conditions on Mars:<p><a href="https://i.imgur.com/BeDg1KM.gif" rel="nofollow">https://i.imgur.com/BeDg1KM.gif</a>