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According to researchers, new answers to the mysteries about Saturn's moons could help us know if Enceladus could support life. For example, researchers may now know why Encelade has a hidden ocean, unlike many of its siblings.
Saturn has not only extraordinary rings, but also more than 60 moons. The size of these natural satellites ranges from tiny moons less than 300 meters wide to the huge Titan, whose diameter is greater than that of the planet Mercury. Many of these moons orbit away from the ringed planet, but others are encrusted in the rings.
Many mysteries remain about the origins and evolution of the deepest moons of Saturn: Mimas, Enceladus, Tethys, Dione and Rhea (ranked in increasing order of diameter, mass and distance from the planet) . Scientists expected the densities and structures of these moons to depend on their mass or distance from Saturn, but the probes analyzing them unexpectedly proved that was not the case.
Related: Saturn Moon Enceladus is the first extraterrestrial "aquatic world" with complex organic materials
Previous search suggested that these moons met from rings of debris around Saturn. According to this idea, the gravitational attraction exerted by the planet would cause powerful tides on these moons, which would lead to churning and melting phenomena, forces driving heavier rocks to sink into the nuclei of the moons and lighter ice to dominate their shells. Such tidal effects would be all the stronger as the moons are closer to the planet and weaker as they move further away over time.
Mimas has no geological activity, although it is the deepest of these five moons and is therefore subject to the highest tides of Saturn. Enceladus, on the other hand, is farther from Saturn and has tides 30 times lower than those of Mimas. However, tidal forces melt the ice inside this moon, leading to a giant underground ocean and "cryovolcanoes" spewing water.
In addition, Rhea is the largest moon and therefore the one that will retain the most heat, which would help to melt its rock and ice and separate its interior in layers, but previous work has suggested that this moon is a mixture of rock and ice. In contrast, Mimas, Enceladus and Dione, which are smaller than Rhea, have rocky-core and ice-shell structures.
Understanding more about the origins of the geological activity of these moons could help answer questions such as whether the hidden ocean of Enceladus could sustain life. "What fascinates me is the quest for a life beyond the Earth," says lead author Marc Neveu, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt. , in Maryland, on Space.com.
To solve the enigmas of these moons, scientists would like to model the effects of the tides on their geology. However, simulations of the orbits at the origin of the tides operate on daily scales, whereas geological simulations generally operate at scales of several million years. Thus, previous work has generally chosen one or the other approach, tidal modeling or geological modeling.
In the new study, however, the researchers devised computer models simulating both the geological changes and the simplified orbital effects that these moons could have undergone during the course of life of about 4,500 billion Saturn.
Scientists have discovered that the tidal forces would lead to sufficient geological activity so that past or present oceans can exist in the interiors of Enceladus, Tethys and Dione. Enceladus probably still has an underground ocean, because its gravitational interactions with other moons such as Tethys and Dione keep its orbit relatively oblong. And the resulting continuous variation in the intensity of Saturn's gravitational attraction regularly alters the level of distortion of the Enceladus shape, flex and heat the inside of the moon.
"This is the first explanation consistent with the data returned by The Cassini probe of NASA for how a small moon like Enceladus, which is only the size of the state of Washington or the British Isles, has an underground ocean while other moons larger or closer to Saturn, and therefore more likely to have such oceans, "said Neveu.
The researchers also discovered that Mimas probably only formed 100 million to 1 billion years ago; if it were older, the interactions between the rings of Mimas and Saturn would have brought this moon to a higher orbit than it currently occupies. The young age of Mimas means that the moon would have formed after all the radioactive materials present during the formation of the solar system were already decomposed about 4.6 billion years ago. As such, his bowels would have been too cold and difficult for the tidal forces to heat up a lot.
"When the ice is warmer and thinner, it becomes more sensitive to the tidal forces that deform," said Neveu. "Mimas did not have the least amount of heat to begin with and for the tidal forces to trigger an extreme warm-up."
As for the reasons why Rhea's entrails could not be separated into layers, "the measurements of the Cassini spacecraft from inside Rhea involve a degree of uncertainty, so it is possible that the deeper layers of its interior are more rocky and that the layers near the surface are more iced, "said Neveu.
Overall, these results suggest that the hidden ocean of Enceladus is about 1 billion years old. "A billion years is enough for life to appear – a billion years after the birth of the Earth, there was life," Neveu said. At the same time, "a billion years means that there can still be enough chemical activity between Enceladus' rock core and its ocean to provide energy to any potential microbial life, similar to the chemical energy present on the seabed that contributes to the preservation of ecosystems Enceladus "The ocean is neither too young nor too old, it may be the right one age for life. "
Neveu warned that one of the main limitations of this research was that it simplified its accuracy. "We have not calculated the high and low tides that every five moons have known at the same time every few hours and 4.5 billion years. it would take about 20 years on a desktop computer, "he said. .
In the future, scientists want to simulate more complex scenarios, by integrating more features about Saturn and its satellites, such as how the planet has been able to win moons that have been hunted or entered. collision with others, said Neveu.
Detailed scientists their discoveries online April 1 in the journal Nature Astronomy.
Follow Charles Q. Choi on Twitter @cqchoi. Follow us on twitter @Spacedotcom and on Facebook.
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