The solar system鈥檚 icy moons may be teeming with tidal waves hidden just under their frozen shells 鈥� which could be promising for any life lurking there.
Enceladus and Europa, the icy moons of Saturn and Jupiter,聽both host subsurface oceans. The thinking is that聽the gravitational pull from the massive planets聽stretches and warps聽the moons, providing enough energy to keep water liquid inside and create waves that bounce between their rocky cores and outer ice shells.
Marc Rovira-Navarro at Royal Netherlands Institute for Sea Research and his colleagues have calculated how these waves propagate in the deep oceans of these small worlds.聽They found that, because of the relative depth of the oceans compared to the size of their frigid moons, the ripples may focus along particular trajectories. That would make them more like jet streams, instead of randomly flowing through the entire oceans.
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As a result, the waves impart most of their energy to the surface in the same spots, which are mostly near the north and south poles, as they bounce back and forth along those lines. Initially, the researchers thought this might explain why Enceladus radiates an inexplicably large amount of heat from its south pole.
Unfortunately, further calculations revealed that the waves likely do not carry enough energy to significantly affect the surface ice. 鈥淚f you were floating in one of these inertial waves you would be moving back and forward at a few centimetres per second,鈥� says Rovira-Navarro. 鈥淚t鈥檚 quite gentle.鈥�
Further calculations taking into account the varying depths of these oceans will reveal whether there might actually be a stronger focusing effect that could affect the ice shells, Rovira-Navarro says. But even if they don鈥檛 affect the moons鈥� surfaces, waves may be important for any potential living organisms in these alien oceans.
鈥淚 can imagine organisms anchored to the sea floor or the ice benefiting from these waves,鈥� says Steven Vance at NASA鈥檚 Jet Propulsion Laboratory in California, because they could move nutrients and energy between the core and the shell. 鈥淚f these standing waves do occur, maybe these spots where they focus are also focal points for life.鈥�
Icarus
