One of the most sought after substances in the Universe is water – especially in its liquid form – as its presence on a planet makes the presence of life (as we know it) significantly more likely. While there are potentially oceans worth of liquid water on e.g. Jupiter’s moon Europa, for now Mars is significantly easier to explore as evidenced by the many probes which we got onto its surface so far. One of these was the InSight probe, which was capable of a unique feat: looking inside the planet’s crust with its seismometer to perform geophysical measurements. These measurements have now led to the fascinating prospect that liquid water may in fact exist on Mars right now, according to a paper published by [Vashan Wright] and colleagues in PNAS (with easy-read BBC coverage).

InSight’s mission lasted from November 2018 to December 2022 by which time too much dust had collected on its solar panels and communication was lost. During those active years it had used its seismometer (SEIS) to use the vibrations from natural marsquakes and similar to map the internals of the planet. Based on rock physics models and the data gathered by InSight, there is a distinct possibility that significant liquid water may exist in Mars’ mid-crust, meaning at a depth of about 11.5 to 20 km. Most tantalizing here is perhaps that at these depths, enough liquid water may exist today than may have filled Mars’ past oceans.

Since we’re talking about just a single lander with a single instrument in a single location, it would be highly presumptuous to draw strong conclusions, and at these depths we would have no means to access it. Even so, it would offer interesting ideas for future Mars missions, not to mention underground Mars bases.