![]() This causes them to align with a certain frequency and their respective gravitational pull deforms their orbits, making them somewhat more eccentric. ![]() For every revolution completed by Ganymede, Europa makes two, and Io makes four. Io, Europa, and Ganymede (in order of proximity to Jupiter) also share an orbital resonance phenomenon. That face also presents a certain bulge precisely because of this attraction. The only possibility is that the heat comes from other sources, such as the gravitational pressure that Jupiter exerts on them.ĭue to the effect of tidal forces, most moons always keep the same face toward the planet. Galilean satellites are icy worlds with rocky, not igneous cores. The existence of such a liquid ocean also implies some source of heat. If confirmed, little Europa could contain two or three times as much water as all the oceans on Earth. Beneath the ice lurks a deep ocean, which models estimate to be 80 to 150 kilometers deep. Some estimate it to be only a few hundred meters. This chaotic picture suggested that the ice cover was relatively thin, perhaps a few kilometers. But in this case, they did not float freely but instead appeared to have refrozen in random positions: the grooves running across their surface had broken and shifted like a badly assembled puzzle, and between the original slabs there were areas where the ice had re-formed without a definite structure. That was the name given to fragments of a few kilometers that were reminiscent of the tabular icebergs that form in the Arctic during the spring thaw. Some of those images showed what came to be called “ice rafts.” There were already hints of the possibility of a global ocean on Europa over 25 years ago, when the Galileo probe, which orbited around Jupiter, passed within a short distance of that moon (about 5,300 kilometers) and transmitted detailed photographs of its icy surface. There are also other possible candidates for which we have insufficient data: Triton, which revolves around icy Neptune and some others such as Dione and the dwarf planets Ceres and Pluto. Scientists suspect that the same is true for two others, although the evidence is less conclusive: Callisto, on Jupiter, and Titan, on Saturn. Today, it is taken for granted that there are at least three worlds in the solar system with global oceans under the surface: Jupiter’s moons Europa and Ganymede and Saturn’s Enceladus. Geyser eruptions, such as those occurring on Enceladus, are not common on Europa, which is unfortunate because their spectrographic analysis would help to establish the existence of dissolved salts, like the sodium chloride in our seas. ![]() The prevailing conditions on Europa’s surface mean that CO₂ is not stable for long. The deposits are concentrated in an area called Tara Regio and are relatively recent. The other more intriguing explanation is that it is a by-product of the decomposition of organic compounds, not living things, of course, but simply carbon compounds such as amino acids or other similar compounds. One explanation is that Europa’s ocean contains large amounts of dissolved CO₂, as is the case with terrestrial oceans. The CO₂ could be of external origin, but it could also have seeped through the subsurface (or sub-ice) itself. This discovery opens up a number of fascinating possibilities. It is covered by a thick layer of ice under which there could be a global ocean. Observations from the James Webb telescope suggest the presence of CO₂ on the surface of Jupiter’s moon Europa. ![]()
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