Recent data sent back to us by the Cassini space probe as it samples the geyser water being shot into space at Saturn’s moon Enceladus, has determined that the moon’s subsurface ocean has a very high pH. The pH is estimated to be around 11 or 12. This would be considered extremely alkaline, but the team analyzing the data concludes that this might improve the odds of supporting life. They point to the alkaline hydrothermal vents, such as The Lost City, on the ocean floor of earth, where warm alkaline fluids flow out into the cold salty deep. There is some thought in the astrobiology community that life on earth may have originated in a similar alkaline vent environment 4.5 billion years ago. The difference, however, is that on early earth the alkaline vent fluid was flowing into an acidic ocean, with a thin mineral wall separating the fluids and allowing a proton gradient to form. It was this proton gradient that generated the energy necessary to transport electrons from molecule to molecule. This is exactly what living organisms do to generate energy – they pump protons across a cell membrane, transport electrons to an ultimate electron acceptor (oxygen in our case), and use the proton gradient to generate ATP (the energy currency of the cell). Cells do the biological equivalent of what the alkaline vents are doing geochemically. For that reason I wonder if the high pH of Enceladus’ ocean really would support the origin of life since it doesn’t necessarily imply situation where a proton gradient would occur.
How Friendly is Enceladus’ Ocean to Life? Astrobiology magazine. Feb. 4, 2016