Jupiter’s Ocean Moon: Tides Replace Sun as Source of Heat & Life

“There’s nothing saying there is life there now.  But we do know there are the physical conditions to support it.”

Richard Greenberg, University of Arizona. world’s leading expert on Europa.

Our understanding of Europa comes primarily from the results of NASA’s Galileo Missions to Jupiter and its moons. Europa is an about the size of our moon, but five times further from the Sun. The distance from the Sun means that Europa formed with less rock and more water -with powerful daily tides generated by the enormous mass of Jupiter 300 times that of the Earth that heats, stresses, and cracks the ice and created the massive global ocean and on-going tectonics and surface change.

 

The key to the possibility of a rich biosphere on Europa is the daily ebb and flow, the tidal friction that created the dominant internal heat source, warming the moon enough to keep most of its thick water layer melted and maintaining its global ocean. A process known as thermosynthesis where Europa’s lifeforms tap thermal energy -the heat generated inside the moon- might have replaced photosynthesis because virtually no light can filter down through the icy crust to the waters below. An environment not unlike that of the extreme life found at thermal vents in the dark depths of Earth’s oceans.

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.

 

Based on what we know about the Jovian moon, parts of Europa’s seafloor could resemble the environments around Earth’s deep-ocean hydrothermal vents.The chances for life there have been uncertain, because Europa’s ocean lies beneath several miles of ice, which separates it from the production of oxygen at the surface by energetic charged particles (similar to cosmic rays). Without oxygen, life could conceivably exist at hot springs in the ocean floor using exotic metabolic chemistries, based on sulfur or the production of methane. However, it is not certain whether the ocean floor actually would provide the conditions for such life.

Its geology and the paucity of impact craters suggests that the top of the ice is continually reformed such that the current surface is only about 50 million years old, roughly 1% of the age of the solar system.

Richard Greenberg of the University of Arizona has considered three generic resurfacing processes: gradually laying fresh material on the surface; opening cracks which fill with fresh ice from below; and disrupting patches of surface in place and replacing them with fresh material. Using estimates for the production of oxidizers at the surface, he finds that the delivery rate into the ocean is so fast that the oxygen concentration could exceed that of the Earth’s oceans in only a few million years.

Oxygen, generated by charged particles striking water molecules on the moon’s surface, would take 1 to 2 billion years to begin seeping into the ocean.That delay would have been critical for supporting life because it would have allowed time for primitive organisms to develop the ability to use oxygen. 

The most fascinating part of Europa’s evolution, says Greenberg, is Europa’s youthful, nearly crater-free appearance, which indicates that the crust is continually resurfaced. Today’s crust is only 50 million years old, even though the moon formed soon after the solar system’s birth 4.56 billion years ago.

Over a period of about 50 million years, a layer of ice 300 meters thick slowly rose from below, gradually covering the moon’s surface and erasing old craters. As a result of this facelift, Europa’s oxygenated layer grew increasingly thick, until after about 1 to 2 billion years the entire ice layer was oxygen-rich. At that point, Greenberg suggests, ice melting at the bottom of the frozen layer began delivering oxygen into the proposed buried ocean at a faster rate than previously estimated, resulting in about 100 times more oxygen in the ocean.

Greenberg says that the concentrations of oxygen would be great enough to support not only microorganisms, but also “macrofauna”, that is, more complex animal-like organisms which have greater oxygen demands. The continual supply of oxygen could support roughly 3 billion kilograms of macrofauna, assuming similar oxygen demands to terrestrial fish.

The best evidence for the question of the origin of life is that there would be a delay of a couple of billion years before the first surface oxygen reached the ocean. Without that time lapse, the first pre-biotic chemistry and the first primitive organic structures would be disrupted by oxidation. Oxidation is a hazard unless organisms have evolved protection from its damaging effects. A similar delay in the production of oxygen on Earth was probably essential for allowing life to get started here.

Casey Kazan

Sources:

http://www.sciencenews.org/view/generic/id/48322/title/Europas_proposed_ocean_could_be_rich_in_oxygen

http://www.physorg.com/news174918239.html

http://www.oceanleadership.org/2009/could-jupiter-moon-harbor-fish-size-life/

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