Icequakes along Enceladus

, Icequakes along Enceladus, #Bizwhiznetwork.com Innovation ΛI

Saturn’s 500-km- (300-mile) diameter moon Enceladus is covered in ice which contains many long fractures or rifts, including fractures called tiger stripes. As the icy moon orbits Saturn, tidal forces cause the tiger stripe fractures to erupt tall geysers of water vapor; this suggests that there is liquid water somewhere beneath Enceladus’ icy surface and that there must be motion along the fractures. Planetary researchers expect that this motion should generate icequakes, similar to earthquakes on Earth. In a new study, they built a model to predict where and when icequakes occur along the tiger stripe fractures, using what they know about ice in Antarctica.
NASA’s Cassini spacecraft captured this stunning mosaic of Enceladus on October 5, 2008 as the spacecraft sped away from this geologically active moon of Saturn. Image credit: NASA / JPL / Space Science Institute.
“Moons like these are places that are exciting because they might have life,” said Dr. Kira Olsen, a geophysicist at NASA’s Goddard Space Flight Center.
“Since life is thought to have first developed in our oceans, liquid oceans under the ice of other worlds could be a good place to search for life.”
“The icy crust of Enceladus might also protect the water below from radiation, making it more habitable.”
“We have ideas of how thick the ice could be, but we don’t have direct observation. Studying icequakes is a way to get at that information.”
To learn more about how Enceladus’ tiger stripe fractures might be moving, Dr. Olsen and colleagues turned to floating ice shelves in Antarctica as the closest analogue on Earth for the types of activity they were seeing on Enceladus.
They analyzed data collected by seismometers along the Ross Ice Shelf between 2014 and 2016 and compared these to satellite images of the area.
They paid particular attention to two seismometers placed next to large rifts on the ice slab.
They related the seismic activity to the stress occurring along these rifts. The majority of icequakes on the Ross Ice Shelf occurred when the rifts were pulling apart, which happens when tides are falling.
The researchers then created models that compared the types of fractures they saw on the surface of Enceladus with those on the Ross Ice Shelf.
These models showed that the largest amount of seismic activity on the icy moon likely corresponded to the tides.
Peak seismic activity there occurs when Enceladus is 100 degrees past the nearest approach to Saturn during its orbit.
The ocean underneath the ice at this point acts something like water inside a sloshing balloon.
The ice fractures are created at the points of highest stress, where the balloon would break apart.
The icequakes aren’t massive along these cracks, even at the peak periods of stress.
The team’s results are valuable to future landed missions to Enceladus or other icy-ocean worlds, where icequakes will help planetary scientists understand what lies beneath the ice.
“Scientists should aim to place seismometers within 10 km (6.2 miles) of these fractures in any future missions to Enceladus to learn more about what’s going on below,” Dr. Olsen said.
“It’s not a quiet out of the way place, but it’s a pretty good place to study.”
A paper on the findings was published in the Journal of Geophysical Research: Planets.
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Kira G. Olsen et al. Projected Seismic Activity at the Tiger Stripe Fractures on Enceladus, Saturn, from an Analog Study of Tidally Modulated Icequakes within the Ross Ice Shelf, Antarctica. Journal of Geophysical Research: Planets, published online May 21, 2021; doi: 10.1029/2021JE006862

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