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And but, defiantly, these alien seas stay liquid.
A Mirror-Wrapped Ocean
Scientists suspect {that a} handful of moons orbiting Jupiter and Saturn—and perhaps even some spinning round Uranus and Neptune—harbor oceans. Hefty Ganymede and crater-scarred Callisto produce weak, Europa-like magnetic indicators. Saturn’s haze-covered Titan, too, very in all probability has a liquid-water subsurface ocean. These “are the 5 that almost all scientists locally really feel fairly confidently about,” mentioned Mike Sori, a planetary scientist at Purdue College.
Together with her colleagues, Margaret Kivelson, an area physicist at UCLA, decided {that a} international ocean is probably going hiding beneath Europa’s floor.
Courtesy of Margaret Kivelson
To date, the one absolute oceanic certainty is Enceladus. “That’s a no brainer,” mentioned Carly Howett, a planetary scientist on the College of Oxford.
Within the Eighties, some scientists suspected Enceladus had plumes; Saturn’s E ring was so clear and glossy that one thing—maybe from one among its moons—should be leaking into area and continuously refreshing it. After Cassini lastly witnessed that planet-garnishing magic in motion, scientists briefly questioned whether or not the moon’s south-polar plumes may be the work of daylight vaporizing ice within the moon’s shell—a bit like dry ice boiling away when heated, maybe by daylight.
“For some time, there was this argument about whether or not there wanted to be an ocean in any respect,” Nimmo mentioned. “What actually nailed that was when [Cassini] flew via the plume they usually discovered salt—sodium chloride. That’s an ocean.” There was nonetheless an opportunity that these plumes may very well be erupting from a smaller, extra remoted sea. However additional Cassini observations revealed that Enceladus’ shell is rocking backwards and forwards so acutely that it should be separated from the moon’s deeper inside by a worldwide ocean.
The plumes additionally pump out hydrogen and quartz, indicators of deep-sea hydrothermal vent exercise, mentioned Frank Postberg, a planetary scientist on the Free College of Berlin. On Earth, such vents produce the warmth and chemistry wanted to energy ecosystems that exist past the attain of daylight—communities of organisms that scientists as soon as thought couldn’t exist in our photosynthetically dependent world.
However what may very well be powering a vent system robust sufficient to warmth a complete ocean? One other moon—this one of many fiery selection—would supply these clues.
The Everlasting, Infernal Tides
In June 1979, a month earlier than Voyager 2’s shut flyby of Europa, scientists introduced that Voyager 1 had glimpsed titanic, umbrella-shaped plumes billowing into area above Io—the eruptive fingerprints of a number of volcanoes.
This commentary ought to have been baffling: Volcanism requires an inside warmth supply, and Io, like the opposite icy moons, ought to have been nothing greater than embers. However a couple of months earlier, an unbiased workforce of scientists had accurately predicted that Io may be a hyperactive volcanic world.