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December 17, 2025<\/p>\n
4 min read<\/p>\n
Add Us On Google<\/span>Add SciAm<\/span><\/span><\/p>\n New Views of Solar System Moons Complicate Ocean Worlds Theory<\/p>\n Oceans hiding within the crusts of distant moons are tantalizing targets for scientists looking for life beyond Earth<\/p>\n By Meghan Bartels edited by Sarah Lewin Frasier<\/span><\/p>\n Titan (left) and Europa (right).<\/p>\n Left: NASA\/JPL\/University of Arizona\/University of Idaho. Right: Image data: NASA\/JPL-Caltech\/SwRI\/MSSS, Image processing: Kevin M. Gill CC BY 3.0<\/p>\n Among the solar system\u2019s hundreds of known moons, few are as enticing as the handful that scientists believe have a global ocean lurking below their crusty surface. But two of these hidden oceans may not be as promising as scientists have hoped, leaving new questions for those interested in the search for life beyond Earth.<\/p>\n Those results come from unrelated research papers, both of which were published on December 17. In one, scientists reexamined data gathered by NASA\u2019s Cassini mission, which ended in 2017, about Saturn\u2019s largest moon, Titan. This research suggests that the moon\u2019s hypothesized internal ocean of water is more of an icy slush, with only pockets of liquid, according to the paper, which was published in Nature. In the other work, scientists used new observations from NASA\u2019s Juno mission about Jupiter\u2019s intriguing world Europa. Their findings suggest that the moon\u2019s icy shell is quite thick, reducing the possibility of the ocean and the surface interacting, according to research published in Nature Astronomy and presented at the annual meeting of the American Geophysical Union.<\/p>\n If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n First, a jaunt to Titan. Of all the worlds scientists have seen up close to date, it\u2019s among the most intriguing. On the surface, Titan is an Earth-like world with a twist\u2014liquid hydrocarbons sculpt a landscape of water ice the way terrestrial seas flow over rock crust. That dynamic geology makes it the only moon with any hope of habitable surface conditions.<\/p>\n And scientists have also wondered whether Titan hid an ocean layer of water and ammonia below that changeable surface. Some interpretations of the Cassini mission\u2019s data have supported that idea: scientists noticed certain surface features moved much more than would be expected if the icy shell lay directly on a solid interior.<\/p>\n But overall, the mission\u2019s data haven\u2019t quite all fallen in line with this theory, leaving scientists dissatisfied. So Flavio Petricca, a planetary scientist at NASA\u2019s Jet Propulsion Laboratory (JPL), and other researchers came together to take a new look at the entire collection of data. They now propose that Titan doesn\u2019t have a global subsurface ocean after all\u2014instead it\u2019s filled with slush, punctured by occasional pockets of full melt. That would be a sea change in how scientists think about Titan, Petricca admits. \u201cSometimes it\u2019s still shocking to think of Titan without an ocean,\u201d he says.<\/p>\n But the new story does manage to pull together all the existing data better than any previous attempt, says Jani Radebaugh, a planetary scientist at Brigham Young University, who was not involved in the new research. And even if that subsurface ocean layer was a mirage all along, the moon itself remains tantalizing, both scientists agree.<\/p>\n Titan\u2019s next robotic visitor will be NASA\u2019s Dragonfly mission, due to launch in July 2028. This car-sized octocopter will whir over Titan\u2019s icy dunes and give scientists an unprecedented look at the moon\u2019s surface. But the mission will also carry a seismometer that will listen to the grumbles and shakes of Titan\u2019s interior\u2014data that scientists will be able to translate into a much better understanding of the moon\u2019s structure.<\/p>\n As tantalizing as Dragonfly\u2019s observations will be, there\u2019s no need to wait for the mission\u2019s interplanetary touchdown to keep delving into Titan\u2019s secrets, Radebaugh says\u2014not when observations from previous missions offer findings like these.<\/p>\n \u201cWe need to keep examining existing spacecraft data,\u201d she says. \u201cThere is always going to be something new that we can find out if we look carefully.\u201d<\/p>\n Although Titan may have lost its global ocean, that of Jupiter\u2019s moon Europa remains scientifically plausible\u2014but it may be trapped under a thicker ice shell than scientists hoped.<\/p>\n To date, researchers\u2019 estimates for the thickness of the moon\u2019s ice crust have ranged from less than two miles to as much as 20 miles (three to 30 kilometers). But those have been only estimates. And the specifics matter because Europa\u2019s crust is riddled with cracks; if the shell is thin enough and the cracks go deep enough, that could let material travel between the icy moon\u2019s surface and its hidden ocean.<\/p>\n New observations of Europa gathered by NASA\u2019s Juno mission, however, suggest that the ice shell is on the thicker side of scientists\u2019 estimates, closer to 20 miles deep\u2014although the exact depth depends on the ocean\u2019s saltiness.<\/p>\n \u201cThere have been theoretical arguments, but this is the first pretty much direct physical measurement,\u201d says Steven Levin, project scientist of the Juno mission and an astrophysicst at JPL.<\/p>\n That calculation is based on data from Juno\u2019s microwave radiometer, an instrument that was designed to peer deep into Jupiter\u2019s atmosphere but that is now turned toward analyzing the planet\u2019s largest moons\u2019 internal structure, too. Remarkably, the measurement was based on only about five minutes of data because of the constraints of the Juno spacecraft\u2019s existing orbit around Jupiter, Levin notes.<\/p>\n The researchers emphasize that their work remains an estimate and that the analysis was limited to a swath of Europa\u2019s equator, which means that the ice shell could still be thinner or thicker in other regions.<\/p>\n And our knowledge of Europa, too, will benefit from future missions\u2014two are already on route to study it and its neighbors. NASA\u2019s dedicated Europa Clipper mission will arrive at Jupiter in 2030, and pinpointing the thickness of Europa\u2019s ice shell is one of its top three agenda items. The European Space Agency\u2019s Jupiter Icy Moons Explorer (JUICE) will arrive at the giant planet in the following year and will provide additional observations.<\/p>\n Editor\u2019s Note (12\/17\/25): This article was edited after posting to include comments from Steven Levin.<\/p>\n If you enjoyed this article, I\u2019d like to ask for your support. Scientific American<\/span> has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.<\/p>\n I\u2019ve been a Scientific American<\/span> subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm <\/span>always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.<\/p>\n If you subscribe to Scientific American<\/span>, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.<\/p>\n In return, you get essential news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-watch videos, challenging games, and the science world’s best writing and reporting. You can even gift someone a subscription.<\/p>\n There has never been a more important time for us to stand up and show why science matters. I hope you\u2019ll support us in that mission.<\/p>\n","protected":false},"excerpt":{"rendered":" December 17, 2025 4 min read Add Us On GoogleAdd SciAm New Views of Solar System Moons Complicate Ocean Worlds Theory Oceans hiding within the crusts of distant moons are tantalizing targets for scientists looking for life beyond Earth By Meghan Bartels edited by Sarah Lewin Frasier Titan (left) and Europa (right). 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