Ice shell thickness reveals water temperature on ocean worlds

Many years earlier than any probe dips a toe—and thermometer—into the waters of distant ocean worlds, Cornell astrobiologists have devised a novel solution to decide ocean temperatures based mostly on the thickness of their ice shells, successfully conducting oceanography from space.

Accessible knowledge displaying ice thickness variation already permits a prediction for the higher ocean of Enceladus, a moon of Saturn, and a NASA mission’s deliberate orbital survey of Europa’s ice shell ought to do the identical for the a lot bigger Jovian moon, enhancing the mission’s findings about whether or not it might assist life.

The researchers suggest {that a} course of known as “ice pumping,” which they’ve noticed under Antarctic ice cabinets, seemingly shapes the undersides of Europa’s and Enceladus’s ice shells, however must also function at Ganymede and Titan, giant moons of Jupiter and Saturn, respectively.

They present that temperature ranges the place the ice and ocean work together—essential areas the place substances for all times could also be exchanged—will be calculated based mostly on an ice shell’s slope and modifications in water’s freezing level at completely different pressures and salinities.

“If we will measure the thickness variation throughout these ice shells, then we’re capable of get temperature constraints on the oceans, which there’s actually no different means but to do with out drilling into them,” mentioned Britney Schmidt, affiliate professor of astronomy and of Earth and atmospheric sciences within the Faculty of Arts and Sciences and Cornell Engineering. “This provides us one other instrument for making an attempt to determine how these oceans work. And the large query is, are issues dwelling there, or might they?”

With present and former members of her Planetary Habitability and Expertise Lab, Schmidt, who’s a member of NASA’s Europa Clipper science workforce, is a co-author of “Ice-Ocean Interactions on Ocean Worlds Affect Ice Shell Topography,” published within the Journal of Geophysical Analysis: Planets. The primary creator is Justin Lawrence, visiting scholar on the Cornell Middle for Astrophysics and Planetary Science (A&S) and a program supervisor at Honeybee Robotics.

In 2019, utilizing the remotely operated Icefin robotic, Schmidt’s workforce, together with Lawrence, noticed ice pumping inside a crevasse beneath Antarctica’s Ross Ice Shelf. Easy and cloudy meteoric ice on the shelf’s base melted, producing brisker, much less dense water that rose up the crevasse and refroze as tough, inexperienced marine ice. Outcomes have been reported in Nature Geoscience and Science Advances, in papers led by Lawrence and Peter Washam, analysis scientist within the Division of Astronomy (A&S).

The method is pushed by the truth that water’s freezing level negatively will depend on stress: As depth and stress improve, water have to be colder to broaden and freeze. Deep down, the place stress is bigger and the freezing level colder, ocean currents can soften ice extra simply. If the melted ice water is buoyant and upwells to shallower depths and decrease stress, it’ll freeze once more. The cycle redistributes some ice inside a shelf or shell, altering its composition and texture.

“Wherever you might have these dynamics, you’d count on to have ice pumping,” Lawrence mentioned. “You may predict what is going on on on the ice-ocean interface based mostly on the topography—the place the ice is thick or skinny, and the place it’s freezing or melting.”

The researchers mapped ranges of potential shell thickness, stress, and salinity for ocean worlds with various gravity and concluded that ice pumping would happen in probably the most possible situations, although not in all. They discovered that ice-ocean interactions on Europa could also be just like these noticed beneath the Ross Ice Shelf—proof, Lawrence mentioned, that such areas could also be a number of the most Earth-like on alien worlds.

NASA’s Cassini probe generated knowledge enough to foretell a temperature vary for Enceladus’s ocean based mostly on the slope of its ice shell from poles to equator: minus 1.095 levels to minus 1.272 levels Celsius. Figuring out temperatures informs understanding of how warmth flows by oceans and the way they flow into, affecting habitability.

The researchers count on ice pumping to be weak at Enceladus, a small moon (the width of Arizona) with dramatic topography, whereas at bigger Europa—practically the scale of Earth’s moon—they predict it acts shortly to easy and flatten the ice shell’s base.

Schmidt mentioned the work demonstrates how analysis investigating local weather change on Earth may also profit planetary science, a motive NASA has supported Icefin’s growth.

“There is a connection between the form of the ice shell and the temperature within the ocean,” Schmidt mentioned. “This can be a new solution to get extra perception from ice shell measurements that we hope to have the ability to get for Europa and different worlds.”