Scientists are discovering that more and more Solar System objects have warm oceans under icy shells. The moons Enceladus and Europa are the two most well-known, and others like Ganymede and Callisto probably have them too. Even the dwarf planet Ceres might have an ocean. But can any of them support life? That partly depends on the water temperature, which strongly influences the chemistry.<\/p>\n
We\u2019re likely to visit Europa in the coming years and find out for ourselves how warm its ocean is. Others on the list we may never visit. But we may not have to. <\/p>\n
<\/p>\n Researchers at Cornell University are figuring out how to determine the temperature of an icy world\u2019s ocean by measuring the thickness of its ice shell and associated properties. They published their results in a research article in the journal JGR Planets. It\u2019s titled \u201cIce-Ocean Interactions on Ocean Worlds Influence Ice Shell Topography,\u201d and the lead author is Justin Lawrence, a visiting scholar at the Cornell Center for Astrophysics and Planetary Science. Lawrence is also a program manager at Honeybee Robotics, a subsidiary of Blue Origin that builds technologies for space exploration.<\/p>\n Their research is based on what\u2019s called ice-pumping, a phenomenon observed under the ice in Antarctica.<\/p>\n \u201cWhen ice is submerged, a melting and freezing exchange process termed the \u201cice pump\u201d can affect ice composition, texture, and thickness,\u201d the researchers write. \u201cWe find that ice pumping is likely beneath the ice shells of several ocean worlds in our solar system.\u201d <\/p>\n Ice pumping is more commonly called thermohaline ice pumping, where thermo means heat and haline means basically the same thing as saline: salty. But whereas saline refers to fresh water, haline refers to ocean water. <\/p>\n On Earth, large-scale thermohaline ice pumping supplies heated water to the north and south polar regions. On a smaller scale, affects how much ice forms on the underside of an ice sheet since ice is formed from water containing no salt or very little salt. So, the salt from the ice-forming water is concentrated in the water under the ice. Since that salt-concentrated water is so close to the ice, the water under the ice is both higher in salt and colder because it\u2019s close to the ice. That\u2019s why the term thermohaline is used. <\/p>\n The high-salinity shelf water (HSSW) that forms under the ice is denser than the surrounding water and sinks. As it sinks, it then becomes warmer than the freezing point there since the water pressure lowers the freezing point. So now the HSSW is warmer and triggers melting on the underside of the ice shelf. Then, the HSSW mixes with lower-salinity meltwater to create colder, buoyant ice-shelf water (ISF.) The ISF upwells and forms soft ice called frazil ice on the underside of the ice shelf. The process can create ice layers hundreds of meters thick.<\/p>\n The critical part is where the ocean and the ice interact. The researchers say that if they can determine the ice thickness, they can constrain the water temperature from afar. The press release presenting the results calls this \u201cconducting oceanography from space.\u201d<\/p>\n \u201cAnywhere you have those dynamics, you would expect to have ice pumping,\u201d Lawrence said. \u201cYou can predict what\u2019s going on at the ice-ocean interface based on the topography\u2014where the ice is thick or thin, and where it is freezing or melting.\u201d<\/p>\n There\u2019s uncertainty around which Solar System bodies have ice pumping and how close ice pumping on Earth is similar to other bodies. For example, if Europa\u2019s ice shell is thicker than about 35 km (22 miles) and has low salt content, then there may be no ice pumping. \u201cHowever, the majority of predictions for Europa\u2019s ice shell thickness suggest that the interface falls in the marine regime, such that Earth\u2019s ice shelves can serve as system analogs to inform European ice-ocean interactions,\u201d the authors write in their research.<\/p>\n Ice pumping is probable on Ganymede and Titan, according to the authors, as long as bulk ocean salinity isn\u2019t too low. On the other hand, Enceladus almost certainly has ice pumping. But the ice pumping on Enceladus is expected to be weaker, while at Europa, it\u2019s expected to be much stronger. <\/p>\n What does it all add up to?<\/p>\n \u201cIf we can measure the thickness variation across these ice shells, then we\u2019re able to get temperature constraints on the oceans, which there\u2019s really no other way yet to do without drilling into them,\u201d said Britney Schmidt, associate professor of astronomy and of Earth and atmospheric sciences in the College of Arts and Sciences and Cornell Engineering. \u201cThis gives us another tool for trying to figure out how these oceans work. And the big question is, are things living there, or could they?\u201d Schmidt asks.<\/p>\n We can only answer that question incrementally right now. To do that, we need to understand the ice shell, the temperature, and how they\u2019re connected to make progress.<\/p>\n \u201cThere\u2019s a connection between the shape of the ice shell and the temperature in the ocean,\u201d Schmidt said. \u201cThis is a new way to get more insight from ice shell measurements that we hope to be able to get for Europa and other worlds.\u201d<\/p>\n Right now, estimates for Europa\u2019s ice shell thickness range from 10 to 30 km (6 to 20 mi). For Enceladus, estimates range from 20 to 25 km (12 to 16 miles), though the south pole region\u2019s ice is much thinner, only 1 to 5 km thick (1\/2 mile to 3 miles.) <\/p>\n Oddly enough, the icy shells and underlying oceans on the Solar System\u2019s icy worlds may be more similar to Earth than any other planets or moons. The interactions between ice and the ocean on Europa are very similar to what researchers see under Antarctica\u2019s Ross Ice Shelf. In 2019, Schmidt and other researchers observed the underside of the shelf with the Icefin robot and observed ice pumping. <\/p>\n Another factor at play here is gravity. \u201cIce pumping scales with gravity and so may prove important to dynamics at the ice shell-ocean interfaces of other similarly massive ocean worlds such as Ganymede or Titan,\u201d the authors explain. That\u2019s one of the reasons that Enceladus is expected to have weaker ice pumping: its gravity is ten times weaker than Europa\u2019s. <\/p>\n This study is important because it shows how ice pumping can occur on different ocean worlds in the Solar System, and that has implications for life.<\/p>\n \u201cWe show that ice pumping can occur for a range of ocean salinity and ice thicknesses relevant to ocean worlds and that ice pumping is an important process linking ice shell dynamics, ocean circulation, and basal ice shell topography,\u201d the authors write. \u201cWe show that the relationship between ice-ocean interactions and ice topography establishes a link between variability in ocean temperature and ice shell thickness that potentially makes constraining ocean temperatures possible in the absence of in situ ocean observations.\u201d<\/p>\n That\u2019s a big step. The more we can learn about these worlds without visiting them, the better. Missions to the Solar Systems icy moons are expensive, though one is already planned: NASA\u2019s Europa Clipper. It\u2019s scheduled for launch later this year and should arrive at Jupiter in 2030. A combination of methods will help the Clipper measure Europa\u2019s ice thickness more accurately.<\/p>\n \u201cThe concepts described here will enable the thermal state of Europa\u2019s upper ocean to be constrained from ice shell thickness,\u201d the authors conclude. <\/p>\n![\"Jupiter's](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2015\/05\/m15-077a-1024x576.jpg\")
![\"Enceladus](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2017\/02\/enceladus_bluevein-580x435-1024x717.jpg\")
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