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Enceladus, a moon of Saturn, may harbor a boiling ocean underground. It is also currently considered a prime location for searching for life beyond Earth. | Image credit: NASA/JPL-Caltech
Small icy moons in the outer reaches of our solar system may be hiding boiling oceans beneath their surface, according to a new study.
Previous research has found that some of the icy moons are in the outer solar system, such as Saturn’s moon Enceladusare not frozen solid. Instead, they could harbor oceans between their ice shells and rock cores. Because continue EarthSince life exists virtually wherever there is water, this has raised hopes that such hidden oceans could be the best places in our solar system to search for alien life.
To shed light on the hidden oceans in these icy moons, geophysicist Maxwell Rudolph of the University of California, Davis, previously examined the forces that could result from changes in the thickness of these moons’ ice shells over hundreds of millions of years.
“We were particularly interested in whether the stresses could lead to the formation of cracks that connect the surface to the subsurface ocean, allowing liquid water to escape from a potentially habitable ocean into space,” Rudolph told Space.com.
In previous work, Rudolph and his colleagues focused on what happens to these moons as their ice shells thicken. Because ice occupies a larger volume than a similar mass of liquid water, freezing puts pressure on the ice shells, creating features such as the “tiger stripes” seen on Enceladus.
In the new study, researchers examined what happens when the ice shells of these moons become thinner due to melting from the ground. For example, previous research has suggested that a wobble in the orbit of Saturn’s moon Mimas may be due to an ocean beneath its icy crust that likely formed in the last 10 million years, as many ancient features such as craters can still be seen on its surface. This ocean likely formed when Mimas’ shell melted due to interactions with other moons of Saturn.
The scientists found that as these ice shells thin, the pressure they put on the oceans decreases. On the smallest icy moons, such as Mimas and Enceladus or Uranus’ Miranda, pressure could drop so low that it reaches a so-called “triple point” – a specific combination of temperature and pressure at which ice, liquid water and water vapor can coexist. This can cause the layers of the oceans closest to their ice shells to boil after the ice shells have thinned by about five to 15 kilometers.
“This is the type of boiling that occurs at low temperatures, not the type of boiling that occurs in the kitchen when you heat water to over 100 degrees Celsius.” [212 degrees F]“Instead, it boils very close to zero degrees Celsius,” Rudolph said [32 degrees F]. So for all potential life forms below this boiling range, life could continue as usual.”
In contrast, for larger icy moons larger than 600 km wide, such as Uranus’ Titania, the pressure drop from melting ice would instead cause the ice shell to break before the triple point for water is reached, the team calculated. The researchers suspect that features of Titania’s geology, such as: B. wrinkle ridges, could be due to a period of thinning of the ice shell and subsequent thickening again.
The gases produced during boiling can have a number of effects, such as the formation of clathrates – complex icy structures that trap gas molecules. “Future work will look at these processes in detail to understand what happens to gas when it is released from an ocean and what types of surface structures we would expect associated with these processes,” Rudolph said.
The scientists detailed their findings online November 24 in the journal Nature Astronomy.
