Richard Greenberg of the University of Arizona proposes that the best place for us to find complex life in the solar system(other than earth,
obviously) is Europa.
New research suggests that there is enough oxygen available in the subsurface ocean of Europa to support oxygen-based metabolic processes for life
similar to that on Earth. In fact, there may be enough oxygen to support complex, animal-like organisms with greater oxygen demands than
microorganisms.
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We believe that there is plenty of liquid water, a subtantial amount of thermal energy from hydrothermal vents as well as energy from the friction and
strain in the surface crust caused by gravitational tidal forces, and now it may turn out that there is enough oxygen to support complex life. The
organisms that made up the base of a food chain on Europa would not be photosynthetic, but would instead employ exotic metabolic processes(known to
exist on earth) based on sulfur or the production of methane, from the hydrothermal vents(which would also supply heat, which is thought to be
necessary). These sulfer and methane basd metabolic processes however, are only sufficient to sustain simple microorganisms if they are earthlike.
The new findings suggest that oxygen levels may be high enough to support more complex life.
This is interesting because it is testable. We can go there and see, and hopefully we will.