Penitentes: spiers of ice over Europe, moon of Jupiter

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The fourth satellite of Jupiter in size, Europe, is one of the most interesting moons in the Solar System, especially for the pursuit of life. A study (published in Nature) suggests that its icy surface of Europa is anything but a skating rink: for researchers (an international team coordinated by Daniel Hobley, of Cardiff University - UK), it could instead be covered with spiers of ice up to 15 meters high.

They are structures that can also be found on the Earth: they are the penitentes (snow penitents), which are formed when the ice sublimates, that is when it passes from the solid state directly to the gaseous state, without passing from the liquid state. For this to happen, temperature and air humidity must be extremely low.

Solar spiers. They are formed when the Sun's rays are refracted in the ice crystals and go to sublimate the ice around the spire, sculpting it. For the process to work, the Sun must be at a peak: this is why on Earth the penitentes are found in the equatorial regions (in the Andes, above 4, 000 meters).

Europe, Jupiter, Galileo probe, ocean of Europe, NASA, extraterrestrial life, Solar System Europe: it is one of the 69 moons of Jupiter, but it is not just any satellite. The icy surface could hide an immense ocean and there, perhaps, there may even be life. The red traces on the ice are what remains of the salts brought to the surface by gigantic geysers. | Nasa

Slow penance. According to the researchers, the thermal and radar images of Europe are compatible with the presence of penitentes. Here too their formation is possible only in the equatorial belt: from 23 ° north to 23 ° south. However, far fewer solar rays arrive on Europe than on Earth, so the process is extremely slow. The researchers calculated a growth of 30 cm every million years .

However, the surface of Europe has not had geological movements in the last 50 million years. And, with an almost inexistent atmosphere, the penitentes were able to stand out up to 15 meters high: "They had a lot of time to do it, " comments Daniel Hobley.

If in doubt … these icy structures would be a problem for a lander, so a future mission should take this into account. A map of the regions where a lander will descend will probably be assigned to missions scheduled for the next decade, when two orbital probes (one from Nasa and the other from Esa) will analyze the molecules fired into space by the gigantic geysers of Europe, in search of traces of life. On those occasions it will be possible to verify the results of the study and possibly also identify the best areas for a safe landing.