Speaking at Harvard in 2011, Carolyn Porco, head of the Cassini imaging research team, reported that the biggest discovery of all had been made at the south pole of Saturn's small icy moon, Enceladus. In the polar region of the satellite, elevated temperatures were detected, as well as a huge plume of ice particles shooting tens of thousands of kilometers into space.
Analysis of the ice footprint, which includes water vapor and trace amounts of organic materials such as methane, carbon dioxide and propane, suggests that it is fueled by geysers erupting from a global ocean buried beneath the moon's icy surface.
These findings, according to Porco, indicate the possibility of the existence of an “environment in which life can inhabit. If we find a second genesis taking place in our solar system, independent of the Earth, it will violate all the canons. The existence theorem has been proven, and we could confidently conclude that life is not a mistake, but a feature of the universe in which we live, and that this is a very commonplace event that happened a staggering number of times."
More recently, Edwin Keith, assistant professor of geophysical sciences at the University of Chicago, called Enceladus "an opportunity for the best astrobiological experiment in the solar system." He added that Enceladus is a leading candidate for extraterrestrial life. Cassini's data strongly suggests that Enceladus's cryovolcanic plumes may have emerged from an oceanic environment friendly to biomolecules.
The preservation of massive explosive cracks on the surface of the sixth largest moon of Saturn, despite the surprisingly cold surface of the moon, remained a mystery for 11 years. More recently, however, scientists at Princeton University and the University of Chicago have shown that cracks can be activated by splashing water in a vast ocean, suggesting that the moon is under a thick ice crust. Such findings lay a powerful foundation for future missions of satellites to Enceladus, which will primarily search for life.
The so-called "tiger stripes", these cracks in Enceladus, regularly eject high jets of steam and frozen particles, fueled by the tidal forces generated by Saturn, scientists write in the Proceedings of the National Academy of Sciences. The four tiger stripes are located near the south pole of Enceladus, an average of 130 kilometers in length and 35 kilometers apart. They were first observed by NASA's Cassini unmanned spacecraft in 2005, which has been orbiting Saturn and its moons since 2004. Cassini's data indicate that the moon's emissions may have originated in a biologically friendly ocean.
Since observing Cassini cracks and ejections, scientists have been trying to explain their cause, size and persistence, explains Edwin Keith.
Promotional video:
“On Earth, eruptions usually don't last too long,” says Kite. - When you see an eruption that is too long, it is due to several eruptions with large gaps in between. It is difficult to explain why the fracture system is not clogged with its own ice. And it is difficult to explain why the release of energy from groundwater does not freeze absolutely everything."
Kite and his co-author Alan Rubin, professor at Princeton Geosciences, developed a model that suggests that water in grooves alternately rises and falls into grooves that bend under tidal stress in Enceladus's icy shell. The heat generated by this regular movement is enough to keep the water from freezing, even if the moon is trapped in ice 30 kilometers thick.
The Kaite and Rubin model provides a seemingly simple explanation for observations that have challenged such simple explanations in the past. Previous suggestions, such as that tiger stripes are slack in ice melted by frictional heating, cannot explain that the erupted material comes from the Enceladus underground ocean. Kite turned to Rubin because Rubin had a history of transporting molten rock through cracks on Earth. But when Kite suggested that viscous motion could keep the water in the grooves from freezing, Rubin was initially skeptical of the idea.
“Because the viscosity of water is so low, I doubted it would produce enough heat,” says Rubin, “but Kaite's calculations showed that it would not only produce enough heat, but it would do so in the time between the peak of tidal stress and peak activity. eruptions. In my opinion, this is the first model that naturally explains observations."
The same model can be applied to other icy worlds like Jupiter's moon Europa, which also has a subsurface ocean and is often referred to as a planetary body capable of having life. “Enceladus can be added to this list. Direct paths to the subsurface oceans on such satellites could be possible windows into an environment that contains life."
Assuming the tiger stripes are indeed associated with the ocean of Enceladus, future satellite missions could be equipped with sensors and equipment to look for possible evidence of life on the moon, Rubin says. The last Cassini flyby around Enceladus took place on 19 December.
Enceladus' tiger stripes regularly spew high jets of steam and frozen particles
Carolyn Porco says the work of Kyte and Rubin may explain a number of questions about the cracks in the satellite.
For example, eruption plumes reach their peak about five hours later than expected, even if we take into account the 40 minutes it takes for ejected particles to reach the altitude at which Cassini detects them. Scientists have previously suggested possible explanations for this delay, including a slow-reacting ice shell.
Kaite and Rubin found that there is an optimal width of the grooves of the tiger stripes that explains the timing of the eruptions. The width of the grooves affects how quickly they respond to tidal forces. In the case of the wide slot, the eruptions respond quickly to tidal forces, Kite says. With narrower slots, eruptions occur eight hours after tidal forces reach their peak. "There's a bull's-eye between them," he says, in which tidal forces convert the movement of water into heat, generating enough energy to produce eruptions satisfying the observed five-hour delay. Porco considers this to be the best point in the study.
Kaite plans to study analogues of Enceladus geysers on Earth, the closest examples of which can be found in Antarctica.