The search for life outside Planet Earth has captivated humanity at large and scientists in particular for generations, and in practice, the search for life starts with the search for liquid water. However, because we can’t simply jaunt out to Enceladus and sample its icy oceans ourselves, we must rely on our understanding of thermodynamics and other physical theory to decipher whether (and the extent to which) liquid water may be present on various moons, exoplanets, and other planetary bodies.

One difficulty in doing this stems from the fact that much of the water we’ve detected outside Earth contains various additional chemical constituents and exists at very high pressures and very low temperatures, presenting a water-thermo parameter space that is dramatically underexplored. For example, to be able to confidently guess whether a solution water and NaCl may exist in a stable liquid form on one of the many icy moons in our solar system, we need not only know the melting points of ice (solid water) and hydrohalite (a solid salt hydrate mineral), but also the fundamental limit of liquid stability, the three-phase eutectic— all at pressures hundreds or thousands time higher than Earth’s atmospheric pressure!

We recently measured the first-ever high-pressure eutectic temperatures of a few simple binary solutions using a new high-throughput isochoric freezing technique, but we’re just scratching the surface. As solutions gain more and more chemical components, the fundamental limit of stability for their liquid phase can decrease in temperature, and these limits for increasingly complex solutions have not only never been measured, but in many cases have never even been guessed at! Furthermore, measuring the phase equilibria is an essential start, but we aspire to greater things— complete thermodynamic descriptions of the energetics, transport properties, you name it, which will enable uninhibited quantitative theoretical exploration of these distant, promising worlds.

The Public Thermo Lab is currently collaborating with members of the NASA Dragonfly Team and many others on blasting our understanding of the thermodynamics of distant icy oceans up into space— if you work in the planetary sciences and think there may be opportunities for synergistic research, please get in touch!