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Parallel Ridges.....Parallel Processes?
Hugh Bollinger

Parallel Ridges.....Parallel Processes?

Europa ice ridges and radar topography (credit: Galelio Mission/JPL/NASA)

Greomorphology is the study of landforms. Whether continental-stretching mountain ranges, oceanic coastlines, vast canyons, or polar icecaps, these physical structures have completely affected climate and the evolution of life on Earth. Have similar landscapes on other solar system bodies had the same effect and created environments suitable for life as well? An elegant study by geo-morphological researchers at Stanford University, and published in Nature Communications, offers an example which could help to answer this question.

The investigators announced they discovered a ice ridge on the Greenland icecap that shares the same parallel geometry as ice ridges on Jupiter's icy moon, Europa, Previous physical analysis of Europa's magnetic field have shown the moon to have a global ocean deep beneath its ice shell. Other forces including Jupiter strong gravity and intense radiation continually interact and affect Europa. These stresses could provide the energy and chemistry required for life to evolve but the ice covering the ocean is many miles thick. How do you study an ocean under such limitations? The Stanford scientists suggest an approach.

They used ice elevation measurements and surface penetrating radar to show that the parallel ice ridges on Greenland were formed by repetitive freeze-thaw interactions and  fracturing. The stresses allowed the central crack, between the ridges, to reach a water system within the ice sheet itself and the ridges grew over time. The Stanford work provides the first observations of double ridge formation over a shallow water body under ice. If the same process is responsible for creating Europa’s ice ridges, this novel study suggests a liquid water system may be near Europa’s surface as well. Such a pool would be far easier to analyze than the far deeper ice-covered sea. Images taken by NASA's Galileo mission and the European Space Agency's Worldview-3 satellite show parallel ridge structures on Europa (a) and Greenland (b) as they currently appear. 

       Parallel ice ridges Europa and  Greenland (credit: Galileo mission, Worldview-3 satellite, Nature Communications)

The surface interactions between ice fractures and freeze/thaw cycles drives the ridge's formation structure. If the same mechanism occurs on Europa, it may not require direct ocean-to-surface geo-thermal geysers or tidal stretching by Jupiter's strong gravity to explore. The new landform study of Europa and Earth has the potential to access and gather samples from the subterranean water sources which may be deposited on Europa's surface or spewed into the moon's thin atmosphere by large geysers. These pressure-produced vents have been observed by the Galelio spacecraft and the Hubble Space Telescope.

NASA's will lanuch a new mission, the Europa Clipper, in 2024 that will go into orbit around Jupiter with specific goals to sample and scientifically measure Europa's surface, interior, and its whispy atmosphere for signs of biology. The 'clipper ship' will carry a slew of scientific instruments to photograph and map the moon's surface; use radar to peer under the ice; to measure surface temperatures that could identify 'hot spots'; and fly through mists ejected from the geysers to collect samples to analyze,, among other tasks.

The environments of Greenland and Europa have many differences from temperature, to radiation, and chemical makeup but the physics of ice formation remains the same anywhere. This offers a way to design and sample Europa directly for life when the Europa Clipper arrives at its fascinating and icy destination. WHB

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