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action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home4/scienrds/scienceandnerds/wp-includes/functions.php on line 6114Source:https:\/\/www.quantamagazine.org\/icy-oceans-exist-on-far-off-moons-why-arent-they-frozen-solid-20231102\/#comments<\/a><\/br> They\u2019d based their prediction on the orbital dance<\/a> of Jupiter\u2019s largest moons. For every four orbits that Io completes, Europa makes two and Ganymede one. This orbital configuration, known as a resonance, causes Io to wobble back and forth, making its orbit elliptical. When Io is closer to Jupiter, the planet\u2019s gravity yanks on it more intensely. When it\u2019s farther away, Jupiter\u2019s tug is weaker. That never-ending gravitational tug-of-war makes the rocky surface of Io move up and down<\/a> by 100 meters, the same height as a 30-story building. These are tides, like Earth\u2019s \u2014 just in solid rock, not water.<\/p>\n Those tides create friction within the moon that generates heat. And that tidal heating is strong enough to melt the rock deep inside Io. \u201cIo doesn\u2019t have a water ocean, but it probably has a magma ocean,\u201d Nimmo said. (Galileo picked up on a secondary magnetic field there too, generated by a global subterranean reservoir of molten rock<\/a>.)<\/p>\n Europa also experiences some tidal heating. But how much those tides warm an ocean depends on where within the moon they occur; in other words, enough of that heat needs to get to the ocean to keep it liquid. \u201cThe tidal heating could be happening in the ice shell itself, or it could be happening in the rocky core underneath,\u201d Nimmo said. Scientists don\u2019t know which is correct \u2014 so they can\u2019t say for sure how much tidal heating contributes to Europa\u2019s liquid interior.<\/p>\n Enceladus, too, is stretched and squeezed by its gravitational tango with a neighboring moon called Dione. In theory this could produce tides that warm the moon\u2019s interior. But the tides created by its resonance with Dione, at least on paper, do not seem to be sufficient to explain its ocean. The numbers don\u2019t yet work, Sori said, and the amount of heat produced isn\u2019t enough to maintain a global ocean for the billions of years since the solar system\u2019s birth. Perhaps, as with Europa, scientists don\u2019t quite know where the tides are creating heat within Enceladus.<\/p>\n Another confounding factor is that orbits aren\u2019t fixed over astronomical time. As planetary systems evolve, moons migrate, and \u201ctidal heating can turn on and off as things drift in and out of different resonances,\u201d said David Rothery<\/a>, a planetary scientist at the Open University in the United Kingdom. Scientists suspect this happened with Miranda and Ariel, two Uranian satellites that may be former dance partners; these moons look as if they were once geologically active but are now arguably<\/a> frozen<\/a> to their cores.<\/p>\n In a similar vein, Enceladus may not always have had Dione as its dance partner: Perhaps their Saturn-circling boogie kicked off more recently and warmed a previously solid moon. But that scenario is also troublesome to explain. \u201cIt\u2019s easier to keep an ocean around and maintain it, rather than freeze and remelt it,\u201d Sori said. Thus, if tidal heating is exclusively responsible for Enceladus\u2019s ocean, then the moon is a veteran dancer that has bopped for several billion years.<\/p>\n For now, the only certainty about this moon\u2019s ocean is that it exists. How it came to be, and how it\u2019s still around today, \u201cis one of the really big unsolved questions,\u201d Sori said. \u201cEnceladus is tough to figure out.\u201d<\/p>\n Fortunately, warm moony interiors don\u2019t exclusively depend on tides.<\/p>\n Half of Earth\u2019s internal heat came from its birth. The rest comes from decaying radioactive elements. Similarly, the rock-rich depths of icy moons should contain a decent amount of uranium, thorium and potassium \u2014 radioactive stores that can cook their surroundings for hundreds of millions, if not billions, of years before they decay into stable elements and stop releasing heat.<\/p>\n Bigger moons will have started out with more bountiful caches of radioactive matter. And perhaps that is all their oceans require. \u201cFor larger moons like Ganymede and Callisto and Titan, they\u2019re sort of inevitable because of this radiogenic factor,\u201d Vance said. Some scientists even argue that Pluto has a subsurface ocean<\/a>. Like the three moons, this dwarf planet is likely insulated by a sufficiently thick crust that slows the leaking of its radioactive furnace into space.<\/p>\n<\/div>\n <\/br><\/br><\/br><\/p>\n
\nThese Moons Are Dark and Frozen. So How Can They Have Oceans?<\/br>
\n2023-11-06 21:58:11<\/br><\/p>\nRadioactive Renegades<\/strong>\u00a0<\/strong><\/h2>\n