Thanks to the analysis of data reported by the Voyager probe, researchers have looked into the five largest moons of Uranus and the possibility of an ocean under their icy crust. And, surprise, four of them could well have one! You will also be interested[EN VIDÉO] Uranus, the first planet discovered by telescope Discover Uranus, an ice giant located three billion kilometers away… Part of its exploration since August 1977, the Voyager 2 probe flew over the planets Saturn, Uranus and Neptune in the 1980s. Thus becoming the very first, and for the moment the only probe that has come so close to the two icy giants. Since then, it has continued its trajectory away from the Sun, and is now more than 19 billion kilometers from Earth. If the data returned on the icy giants have already been studied in part, they have just been revisited by researchers in a publication of Journal of Geophysical Research. All with the aim of looking for traces of a liquid ocean, yet considered improbable in these cold satellites. “When it comes to small bodies – dwarf planets and moons – planetary scientists have already found evidence of oceans in several unlikely places, including the dwarf planets Ceres and Pluto, and Saturn’s moon Mimas,” said in a press release Julie Castillo-Rogez, first author of the study and scientist at NASA’s Jet Propulsion Laboratory. “So there are mechanics at play that we don’t fully understand. This article investigates what they might be and how they are relevant to the many bodies in the Solar System that might be water-rich but have limited internal heat. » If little heat escapes, the water could still be liquidA total of 27 moons surround Uranus, but it is the five largest Uranian moons that have been analyzed, in descending order of mass: Titania, Oberon, Umbriel, Ariel and Miranda. With Titania, the largest, having a diameter of 1,580 kilometers twice smaller than that of Europe. According to the study, if one of these bodies contains an ocean, its thickness will not exceed 50 kilometers, or even 30 kilometers for Arien and Umbriel. An estimate made through modeling of the internal structures of each satellite, based both on knowledge of other known moons such as Charon and Ceres, and on data from Voyager 2 and observations made on the ground. Their conclusion for Miranda is not very encouraging: if the Uranian moon had hosted an ocean, it would already be frozen! Indeed, the models show that it loses heat too quickly because of its fragmented surface, and that no phenomenon would make it possible to heat it sufficiently. For others, an ocean is possible! The porosity evaluated by the researchers turns out to be much lower, meaning that they lose much less heat. But also create very few. “Therefore, the current thermal budget of these moons is limited to long-lived radioisotopic decay,” the study describes. A potentially habitable ocean on Titania and OberonIt was during their formation that everything would have happened, in particular its differentiation with that of inclusions rich in calcium and aluminium. Indeed, this difference then determines the quantity of short-lived radioisotopes which will have been accreted and will then be able to release heat! Insufficient, however, to be responsible for all the heating. With the exception of the case of Ariel, for which cryovolcanism has been observed, if it formed early enough, the heating by the decays of aluminum (26Al) could have been sufficient to trigger the melting of the ice. Otherwise, tidal effects during a passage in resonance with another satellite could also have caused at least partial fusion. And this same passage would then have “closed” the surface of the moon, allowing it to keep its internal heat! The same observation has been made for Umbriel, which could thus harbor an ocean 10 to 15 kilometers thick. For Titania and Oberon, the results are all the more positive: being more massive, the tidal effects due to Uranus allow more intense heating, an effect which is added to the two others mentioned above! They could thus shelter a thicker ocean, and above all warmer, and therefore potentially inhabited! The study adds that “Recent ground-based telescope observations of Uranian moons have detected carbon dioxide (CO2) ice and possibly ammonia (NH3) and ammonium (NH4) containing species. on their surfaces”, elements with antifreeze properties. One could finally consider that these oceans would rather be “relics” of ancient oceans than thick oceans. And the challenge will then be to detect them. “These residual oceans could still be detectable by in situ magnetic sounding, provided that their temperatures do not drop too much below the freezing point of water (≲245 K)”, details the study. Digging the surface of the moons would also be effective in determining the presence of different elements! Future work by the researchers, their study describes, will instead focus on “the implications of increased tidal warming due to resonance crossing on the global evolution of the moons.”