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The astronomer Rafael Bachiller reveals to us in this series the most spectacular phenomena of the Cosmos.

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Enceladus, an icy moon of Saturn, has spectacular geysers that shoot water into space.

It was assumed that such geysers came from a deep subsurface ocean, but a new study now casts doubt on that.

Deep ocean

Although only 500 kilometers in diameter (7 times smaller than that of our Moon), Enceladus is one of the most interesting bodies in the solar system.

Its surface is very rich, with old areas full of craters and other younger areas renewed by tectonic activity.

But what is most surprising about this small world are the more than a hundred geysers that, in the area of ​​its south pole, throw water vapor into space.

The structure of EnceladusNASA/JPL

These jets were discovered by the Cassini space probe when it flew by the small moon in 2005. Since then, it has been found that, in addition to water, such plumes also contain ice particles, common salt crystals, ammonia and even some organic compounds. .

Studies of the structure of this moon, carried out over almost two decades, have revealed that its surface is a thick icy crust some 30 to 40 kilometers thick, under which lies a liquid ocean that can be between 10 and 30 kilometers deep and finally a rocky core.

Cryovolcanoes

Geysers on Enceladus appear to erupt from surface striations called "tiger stripes."

Until now it was thought that these striae must be geologically similar to the great mountain ranges and subduction zones of the Earth, where volcanoes form.

Therefore, these geysers seemed to be directly connected to the deep subsurface ocean.

Frictions due to small earthquakes, or tectonic activity on the small moon's surface, could melt some of the ice on the surface and create the striated fissures from which geysers would emerge carrying water from the ocean into space.

fit for life

It is still a mystery how the water in that ocean remains liquid, and what is the mechanism by which it is relatively warm.

Perhaps the source of the energy lies in the strong tidal forces due to the gravitational pull of the giant Saturn.

Be that as it may, this liquid ocean, which must be rich in salts, offers conditions that seem very suitable for the emergence of life.

Along with Jupiter's moons Ganymede and Europa, which also contain large oceans beneath their surfaces, Enceladus' ocean is one of the most interesting places to search for extraterrestrial life in our solar system.

Until now it was thought that the study of the chemical composition of the geysers would reveal the composition of the ocean to which they seemed to be directly connected, thus offering some clue about the possible existence of life.

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Planetary scientists Colin Meyer and Jacob Buffo, from Dartmouth College (a private university in New Hampshire, USA), are dedicated to studying and making numerical models to simulate the behavior of terrestrial ice and polar seas and those of icy moons of the solar system.

At a recent meeting of the American Geophysical Union, a team coordinated by these researchers presented simulations showing the possibility that the geysers on Enceladus do not arise directly from the ocean, but could be created in pockets of muddy water on the icy crust. .

And the chemical processes taking place in the moist mush of these puddles might not be the same as those in the much deeper liquid ocean.

This work therefore constitutes a serious warning with a view to the conclusions that can be drawn from the properties of geysers.

It now seems possible that these properties were not, after all, identical to those of the deep ocean of Enceladus.

And this is something that must be taken into account in the design of the numerous space missions that are under study by different space agencies, such as the North American NASA and the European ESA.

The hope that taking samples of the water ejected by the geysers would be enough to reveal the chemical composition of the ocean, without having to drill, may not be entirely substantiated.

If no signs of life were found in the geysers, this would not imply that they could not be found in the ocean.

Meyer, Buffo and colleagues' paper titled "A mushy source for the geysers of Enceladus" was presented at a recent American Geophysical Union meeting in New Orleans.

The abstract of the work can be consulted at this link.

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Rafael Bachiller is director of the National Astronomical Observatory [https://bit.ly/3GzKALD] (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain.

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