A New Desalination Pump Helps Define the pH of Ocean Worlds

Abstract

We study ocean exoplanets, for which the global surface ocean is separated from the rocky interior by a high-pressure ice mantle. We describe a mechanism that can pump salts out of the ocean, resulting in oceans of very low salinity. Here we focus on the H 2 O–NaCl system, though we discuss the application of this pump to other salts as well. We find our ocean worlds to be acidic, with a pH in the range of 2–4. We discuss and compare between the conditions found within our studied oceans and the conditions in which polyextremophiles were discovered. This work focuses on exoplanets in the super-Earth mass range (∼2 M ⊕ ), with water composing at least a few percent of their mass. However, the principle of the desalination pump might extend beyond this mass range.