If the scientists' conclusions are correct, then near-surface processes associated with liquid water on Europa may be more important than previously thought and should be taken into account when assessing its habitability.
Geophysicists have determined that the mechanism responsible for the formation of icy twin ridges in Greenland and Jupiter’s moon Europa may be the same. It is assumed that in both cases, the ridges grow due to the displacement of liquid water from near-surface reservoirs, which gradually freeze through.
Surface features of Jupiter’s Moon Europa
Jupiter’s icy moon Europa is considered the most suitable object in the solar system, which could potentially host extraterrestrial life forms.
Europa has a global subsurface ocean hidden under an ice crust that is estimated to be 20 to 30 kilometers thick. The ocean does not freeze due to the influence of Jupiter’s tidal forces on the interior and generates water geysers.
Europa’s surface is young and geologically active, showing a wide variety of landforms such as ridges, depressions, bands, lenticules (dark spots), or a chaotic landscape. The most common are double ridges, separated by depression, with a ratio of height to distance between the tops of the ridges of less than 0.58.
These structures can extend for hundreds of kilometers; cryovolcanism, the influence of tidal forces, diapirism, compression processes, and dike intrusion are proposed as possible mechanisms for their formation. (or cryofracturing) and shear heating.
All of these mechanisms require the destruction of the ice crust and, with the exception of compression and diapirism, cause ice-water interaction near the moon’s surface, either due to the melting of ice due to internal heating or due to the influx of water directly from the subsurface ocean.
Scientists compared ridges in Greenland and on Europa, and they are strikingly similar
A team of geophysicists led by Stanford University’s Riley Culberg set out to understand the nature of Europa’s twin ridges by analyzing satellite observations of the double ridge found in Greenland and then using computer simulations of processes on Jupiter’s icy moon.
The double ridge found on Earth is located about 60 kilometers from the edge of the ice sheet in northwestern Greenland and consists of two quasi-symmetrical ridges 800 meters long, separated by a central depression about 46 meters wide. The ratio of the average height of the ridges to the distance between their peaks is 0.37.
Analyzing data from radar observations of the ridge in Greenland, conducted between May 2015 and March 2017, scientists determined that the formation of the ridge took place in several stages.
In the first stage, a subsurface reservoir (pocket) was formed due to the runoff of surface meltwater through a porous layer of ice onto a thick base of stronger ice. In the second stage, the pocket began to freeze and collapse due to internal overpressure or stresses, and water rose to the surface along a large crack.
In the third stage, the water in the central channel froze again, forming an impenetrable ice plug, and in the final stage, a double ridge formed, when the water under pressure inside the freezing pocket came out through cracks on either side of the channel, creating ridges.
The scientists concluded that low gravity and atmospheric pressure near Europa’s surface should contribute to the formation of double ridges by a similar mechanism.
This process does not require a direct connection of the ocean to the surface through cryovolcanism, but pressurized ocean water or ice melt due to shear heating or diapirism can create large subsurface pockets of liquid water that can refreeze.
If the scientists’ conclusions are correct, then near-surface processes associated with liquid water on Europa may be more important in shaping its surface morphology than previously thought and should be taken into account when assessing its habitability.
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• Culberg, R., Schroeder, D. M., & Steinbrügge, G. (2022, April 19). Double ridge formation over shallow water sills on Jupiter’s moon europa. Nature News.
• Kluger, J. (2022, April 21). New clues to possible life on a moon of Jupiter. Time.
• Mack, E. (2022, April 20). New Data tied to Jupiter Moon Europa is good news for alien believers. CNET.
• Rao, R. (2022, April 21). Icy Europa’s mysterious double ridges may hint at hidden pockets of water. Space.com.