The Thermodynamics of Life without Sunlight
On Earth there are deep-sea hydrothermal vents where sunlight never penetrates but certain bacteria manufacture food from minerals. To do this they use the oxygen dissolved in the water. But how does oxygen get into the water? It comes from photosynthesis just under the surface of the sea. Chlorophyll in floating seaweed and plankton releases oxygen, but most of the oxygen dissolves in the water rather than going into the atmosphere. Ocean currents mix the surface water with water in the depths, distributing the oxygen all the way to the bottom. This process goes on continuously. Oxygen is very reactive. Oxygen gradually combines with other elements to make minerals. If contamination kills the seaweed and plankton or keeps sunlight from reaching the surface, eventually there will be insufficient oxygen to sustain life near the deep sea vents.
Knowing thermodynamics and the role of chlorophyll in sustaining life allows us to evaluate the idea some NASA people are advancing, that they may find life under the ice of Europa, one of the moons of Jupiter.[i] Europa possibly has liquid water layers under its frozen surface. The powerful gravity of Jupiter may cause tidal effects strong enough to heat and melt some subsurface parts of the ice. The overlying ice layers may supply the pressure water needs to keep from boiling away. But the water under the ice layers will not have any dissolved oxygen in it. Even if photosynthesis or some other process made free oxygen from the weak sunlight incident on Europa’s surface, the oxygen could never work its way down through the surface ice into the liquid layers below.
Surely NASA has scientists who know what we just explained above. Certain budget dynamics keep NASA scientists from gross sensationalism. The problem is that the possibility, however far-fetched and evanescent, of finding alien life is so sensational that it bypasses reasonable scientific caution and leads the popular mind astray.
[i] Johnson, Torrence V., “A Look at the Galilean Satellites after the Galileo Mission,” Physics Today, 57 (Number 4, April 2004), pp. 77–83.
Knowing thermodynamics and the role of chlorophyll in sustaining life allows us to evaluate the idea some NASA people are advancing, that they may find life under the ice of Europa, one of the moons of Jupiter.[i] Europa possibly has liquid water layers under its frozen surface. The powerful gravity of Jupiter may cause tidal effects strong enough to heat and melt some subsurface parts of the ice. The overlying ice layers may supply the pressure water needs to keep from boiling away. But the water under the ice layers will not have any dissolved oxygen in it. Even if photosynthesis or some other process made free oxygen from the weak sunlight incident on Europa’s surface, the oxygen could never work its way down through the surface ice into the liquid layers below.
Surely NASA has scientists who know what we just explained above. Certain budget dynamics keep NASA scientists from gross sensationalism. The problem is that the possibility, however far-fetched and evanescent, of finding alien life is so sensational that it bypasses reasonable scientific caution and leads the popular mind astray.
[i] Johnson, Torrence V., “A Look at the Galilean Satellites after the Galileo Mission,” Physics Today, 57 (Number 4, April 2004), pp. 77–83.
