The famous “tiger stripes” by Enceladus are rumbling: Researchers provide clues as to how the sloshing of the ocean inside Saturn’s moon causes tremors in the crevices in its ice crust. Investigations on ice shelves in the Antarctic show that the strongest vibrations occur due to tensile stresses in the context of tidal effects. From this, the researchers were able to draw conclusions about the seismic activities in the ice of Saturn’s moon. As they explain, one day direct measurements of the icequakes could provide information about the thickness of the armor that envelops the potentially life-friendly ocean.
In recent years, the little Saturn moon Enceladus has become a celebrity among the celestial bodies in our solar system. Because one assumes that there is an ocean of liquid water under his ice armor. The reservoir is noticeable through fountains of ice that emerge from cracks at the south pole of the moon. The Cassini space probe even succeeded in snapping up some water ice in its flyby, which was escaping from these structures known as “tiger stripes”. The analyzes showed: the water is salty and contains organic molecules. This makes the moon a potential extraterrestrial habitat. Just recently, a study provided new evidence that the methane detected in the water vapor fountains could actually come from microbes.
It seems clear: The possibly life-friendly warmth inside the moon and the cracks in its ice shell are ultimately due to tidal forces. While Enceladus moves its orbits around Saturn, it is literally kneaded by the gravitational effects. This creates frictional heat and deformations and cracks occur, from which water can apparently also be squeezed out. It stands to reason that this geological activity is also associated with seismic activity. However, there is no detailed information on the possible earthquakes in the ice. “So far, there is also no direct information about the thickness of the ice. Research into ice quakes could provide insights into this, ”explains Kira Olsen from NASA’s Goddard Space Flight Center in Greenbelt.
Comparative view of the earthly
To gain clues as to how the ice moves in the Enceladus tiger stripes area, Olsen and her colleagues turned to studying earthquakes in the floating ice shelves in Antarctica that are exposed to the effects of the tides. Since some of their surface features are similar to the structures on Saturn’s moon, they can allow conclusions to be drawn about processes in the ice of Enceladus, the scientists explain. As part of their study, they analyzed data collected by seismometers along the Ross Ice Shelf on the southern continent and linked it to satellite images of the structural features of the ice there. They paid particular attention to two seismometers placed near large cracks on the ice sheet.
The investigations clarified the connection between the seismic activities and the stresses that occur along the cracks. Most ice quakes occurred on the Ross Ice Shelf when the ice in the area of the cracks was stretched due to the water movement of the tides. The scientists then projected these results onto the tiger stripes of Enceladus, which are strikingly similar to the fissure structures in the earth’s ice shelf: They developed models that show what seismic activities could occur there.
It rumbles and cracks
The models indicate that the peak of seismic activity on the Tiger Stripe occurs when Enceladus is in its orbit 100 degrees after the closest approach to Saturn. In the area at the South Pole, there are obviously strong tensile stresses. According to the researchers, the reason for this pollution is that the ocean under the ice behaves similarly to water in a billowing balloon. The ice breaks then occur at the points with the highest stress. If the stresses there are predominantly compressive, the seismic activity only reaches 50 percent of the peak values, according to the model simulations. The ice quakes are not violent and sudden, even at peak loads, emphasize the scientists: “It probably rumbles and cracks continuously in the icy underground,” says Olsen.
Mark Panning from the California Institute of Technology in Pasadena, who was not involved in the study, sees the results as an important step towards understanding the geological processes on the mysterious Saturn moon and beyond. “The study shows possibilities to investigate how the geological activity could be connected to seismic effects on Enceladus and other tide-activated icy worlds: Analogies to terrestrial structures and effects can provide us with clues,” comments the scientist.
In conclusion, Olsen and her colleagues emphasize that one day seismic data could also provide important further insights into the icy worlds with warm hearts: “Our results are valuable for future land missions to Enceladus or other ice-covered worlds, where seismic activity could give us clues, what lies under the ice, ”write the scientists.
Source: American Geophysical Union, professional article: Journal of Geophysical Research – Planets, doi: 10.1029 / 2021JE00686