the moon with twice as much water as our planet.

Look to the sky. Somewhere in the blackness is Europe. Galileo discovered it in 1610 using just a rudimentary telescope. Not that it hides too much, and yet its depths could harbor the answer to one of the biggest questions humanity has asked itself: are we alone?

The Earth is not the only body in the solar system with water, Mars hides it frozen in the permafrost of its poles and comets walk it from one side to the other of the Cosmos, but there is a satellite that ridicules the rest of the contestants: Europe . It is barely the size of our moon, at 3,100 kilometers from side to side, but on its small surface there is more water than in a comet, more than in Martian permafrost and even more than on our planet. In fact, it not only surpasses us, it almost doubles the amount of terrestrial water. Oh, and this time there is no trick, because it is liquid water.

How do we know?

Scientists are pretty sure that a 90-kilometer ocean stretches under the first 25 kilometers of ice, almost 20 times more than the average depth of the Earth’s hydrosphere. The water surrounds a solid rock mantle whose heart houses a core of iron and nickel, very similar to that of our planet. But, if the ice that covers it is so thick, how can we know all this?

Oddly enough, the trick is precisely on its surface, without drilling anything. In fact, it would be a shame to pierce its surface, because Europe is the “smoothest” body in the Solar System. On the ice there are almost no crater marks or large mountains, which raised suspicions. Why is there hardly any craters? It is not logical to think that the cosmos has punished Europe less than its neighboring moons that are strewn with holes, so there must be something that has “cleaned” all the remains of impacts from its surface. Well, it turns out that we know very well what a crater can eliminate and it is a constant renewal of the crust, as occurs on Earth with the ocean floor, which is created and destroyed in an endless cycle.

Furthermore, despite the fact that Europe is estimated to be 4.5 billion years old, its area is between 20 and 180 million. This is how we know that the surface of this moon is renewed following principles similar to those of our plate tectonics. In our case, the crust plates move on the mantle, more plastic and hotter than the surface. In the case of Europe, it is expected that there is something fluid under the ice to allow it to move, as if it were a ice pack. But there is more, because this would also explain the strange lines that cross it, which could have been areas where the ice broke, exposing an ocean that quickly froze again. As if this were not enough, in December 2013 something magnificent happened. The Hubble Space Telescope detected two jets of liquid water coming out under pressure from the southern hemisphere of Europe, confirming the theories. Although in everything I have told you there is something suspicious and you may have noticed.


Astrobiologists are wondering where to look for life off Earth and one of the keys seems to be that there is liquid water, because we know that it works wonderfully as a solvent to facilitate the chemical reactions that allow us to live. This does not mean that it is considered a necessary criterion for the emergence of life, but we have to be practical and it is the only solvent that we know 100% that can fulfill these biological functions. We could compare it with deciding where to go to eat based on how full we see the restaurant. Of course, an empty restaurant can serve delicious food, but if we need to play it safe because we lack time, we will not hesitate to enter the most crowded.

And that’s the key point, because to find out where we can find water, scientists trace a kind of ring around the stars. Based on the size and temperature of the star, it is calculated from how far the environment cools enough to allow liquid water to exist. Similarly, it is calculated how far the temperature drops so much that it freezes. Colloquially, this strip is called the “Goldilocks zone” because it is neither too cold nor too hot, but at a perfect intermediate point for life forms like us.

The truth is that there have been many different estimates depending on what additional factors have been taken into account when calculating it, but generally there are only three planets in our solar system that fall in that “paradisiacal” strip: Venus, Earth and Mars. . This is where the problems begin, because we have said that Europe is a moon of Jupiter, which is well outside this range with its maximums of -163 °C and minima of -223 ° C. In fact, this moon is not the only one with a heart of liquid water, and that its “sister”, Enceladus, is even further from the Sun, orbiting Saturn. How can it be?

Well, because really, that there may be liquid water in the Goldilocks area, does not mean that it is the only place to find it, because not all water is heated by the brightness of the Sun and these two frozen moons have found alternative energy sources.

The heat of the tides

Jupiter is enormous, its gravitational force is tremendously great and that means that Europe is deformed by them, as if they were lengthening it towards the planet. This traction is called “tidal force”, because it is what causes the sea level to rise in one area and fall in others, since water deforms more easily than the land on which it rests. This is added to the fact that Europe is a participant in a curious phenomenon, the Laplace resonance. This means that Europe and the other main Jovian satellites are synchronized. For each turn that Ganymede completes around Jupiter, Europe makes two and Io gives four. By being accompanied, they deform Europe together, making the tidal forces even more intense and melting its interior like a huge coulant cosmic.

It is not the same, but understanding it intuitively we can use an elastic rubber. Let’s cut it and take its ends, one with each hand. Now let’s stretch it to the maximum, wait a second and put our hands back together to release the tension. But don’t waste time, as soon as you do the latter press the rubber between your lips. You will notice how the deformation has heated it up. What happens with Europe is not exactly the same, but it helps to visualize it. Now there is only one question left to ask. If there is liquid water: is there life in Europe or Enceladus?

We do not know

It is a forceful title, of course, but I don’t want it to be confusing. It is common to find overly enthusiastic interpretations of what you will read below, but let’s remain calm, because there is no conclusive evidence and for every clue there is a possible explanation that does not include life.

With so much water it is normal that we have looked at these moons. It is tempting to imagine what kind of beings can live under 90 kilometers of ice, but possibly reality would have nothing to do with our fantasies. If life existed there, most likely they were tiny, almost microscopic beings. Although we better stop imagining life forms and think, what evidence is there?

Being so far away, the best thing we can do is analyze the atmosphere and the water jets with spectroscopy techniques. When light bounces off certain chemical elements, it is marked by a kind of fingerprint. Analyzing the light that comes from Europe and Enceladus we can get an idea of ​​what compounds are there.

Apparently, in the atmosphere of Europe there are large concentrations of oxygen and hydrogen, in the jets of Enceladus we have found ammonia, but little else. Based on this, risky interpretations of the origin of some of these substances have emerged, suggesting that they may be due to biological processes present on Earth. The reality is much leaner: we don’t know what it implies.

The evidence is absolutely insufficient to do more than speculate and depart from science to give us the license to dream. Dream of gaseous creatures walking upside down, floating below the thick layer of ice. Or maybe, imagining huge blind invertebrates, condemned to communicate with songs like those of whales. Maybe someday we will reach the mysterious ocean to find fumaroles at its bottom, surrounded by life, warming the cold ocean.


  • None of the alleged signs of life is even minimally conclusive. To speak of life under the icy crust of these moons is pure speculation.
  • Although we are pretty sure that Europe hides a giant ocean, the plumes of water emerging from Enceladus may have a more modest origin. It is suspected that they may be emitted by a single water bag at the south pole. The reason is that it is the only place where water has emerged and no evidence of plate tectonics has been found on its surface, as was the case in Europe.
  • The strongest hypothesis for the plumes seen only at the south pole of Enceladus is that its (possible) underground ocean is regional, located in the southern hemisphere, with a very small thickness compared to the ice sheet.



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