New research published this week in Nature Astronomy suggests subsurface oceans on icy moons like europa and Enceladus may be far more dynamic than previously thought. Simulations reveal these hidden oceans could experience boiling at surprisingly low temperatures due to fluctuating pressure from their icy shells. The findings, stemming from work at NASA’s Jet Propulsion Laboratory and the University of Washington, offer a new lens through which to view the potential for habitability, and could explain geological features observed on these distant worlds.
Recent simulations suggest that subsurface oceans on icy moons throughout the solar system may experience a surprising phenomenon: boiling. The research, published in Nature Astronomy, indicates that variations in the thickness of these moons’ icy shells could create conditions where seawater boils even at extremely low temperatures.
Several smaller moons in our solar system, including Enceladus (a moon of Saturn) and Europa (a moon of Jupiter), are believed to harbor vast oceans beneath their icy crusts. These hidden oceans are considered prime locations in the search for extraterrestrial life. The presence of ice, which expands when it freezes, exerts pressure on the underlying ocean and contributes to geological features like the “tiger stripes” seen on Enceladus’ surface.
Previous studies have linked orbital wobbles of some of these moons to the presence of subsurface oceans. Researchers have now focused on understanding what happens when the ice shell covering these moons thins and thickens due to tidal heating from their parent planets. This latest work explores the implications of a thinning ice shell on the ocean below.
The new research reveals that when an icy shell thins in certain areas, the pressure on the ocean below decreases. This pressure can drop to a point known as the “triple point,” where ice, liquid water, and water vapor can coexist. Under these conditions, the surface water of the ocean can “boil” directly into vapor. This discovery offers a new perspective on the potential habitability of these icy worlds.
Unlike the familiar boiling point of 100°C, this process occurs when the ice shell is between 5 and 15 kilometers thick and the pressure is reduced to a critical level. Liquid water then evaporates into gas at temperatures just above freezing (0°C). This process continues until the ice shell thickens again and the pressure increases. The findings suggest that the dynamics of these subsurface oceans are more complex than previously understood.
Smaller icy moons like Enceladus, Europa, and Triton are most likely to experience this boiling effect. Enceladus is of particular interest, as evidence suggests its ocean may have formed relatively recently. The “tiger stripes” on Enceladus, the mysterious coronae and cliffs on Triton, and similar features on other icy moons may all be linked to this subsurface ocean boiling. This research could reshape how scientists interpret surface features on these distant worlds.
Beyond explaining unusual surface features, the new theory provides a fresh set of criteria for evaluating the potential for life beyond Earth. Even if the surface of a subsurface ocean is boiling, the deeper layers could remain liquid and potentially support life. This expands the range of conditions considered habitable in the search for extraterrestrial organisms.
（首圖來源：AI 生成）
