Liquid water may exist not only deep beneath the icy shell of Jupiter’s moon Europa, but also in the icy crust itself, a study suggests. This suggests the similarity of double ridge grabens on the surface of Europa with an ice structure in Greenland, the origin of which the researchers investigated. As in the terrestrial version, the prominent rifts could have been formed on Europa by the effect of water pockets in the ice relatively close to the surface. The new evidence of the complexity of Europa’s icy crust reinforces the Moon’s reputation as a possible additional home for life in the Solar System, the researchers say.
At first glance it looks cold and dead – but Jupiter’s moon Europa has it all, as studies have shown in recent years. It is now believed to have an ocean of liquid water beneath an ice crust that is probably many kilometers thick. This makes the celestial body one of the hottest candidates in the search for extraterrestrial life forms. Given the amazing adaptability of life on Earth, it seems possible that organisms may have evolved in the hidden waters of Jupiter’s icy moon.
Numerous surface structures that testify to its geological activity are considered an important indication of the multi-layered structure of the moon. They are thought to be partly due to the slow rise and fall of ice masses. A particularly striking feature on the surface of Europa are the many so-called double ridges, which would result in an M-shaped structure in a lateral cross-section. The ridges can sometimes be more than 300 meters high and are separated by valleys, some of which are almost a kilometer wide. The processes by which these double combs are formed are still unclear. The study by a research team from Stanford University now sheds new light on this question.
Icy twin combs in sight
As the scientists report, they came to the research topic indirectly, because they had actually previously dealt with the effects of climate change on the Greenland ice sheet. But when a researcher gave a lecture on the moon Europa, her field of research expanded: “In the images shown of the double ridges, I noticed that they resemble a structure that we had just looked at in more detail in the case of the Greenland ice sheet,” says first author Riley Culberg. It emerged that the M-shaped ridge in northwestern Greenland could represent a miniature version of the prominent feature on Europa.
It was therefore obvious that similar processes lead to formation in both cases. In the case of the Greenland double ridge, the scientists were able to clarify this using radar data and modeling of the processes. The underlying structure was found to be a pocket of pressurized liquid water in the ice. The double ridge on the surface is caused by repeated freezing processes and fractures, which ultimately pushes two peaks up, the scientists explain.
Water reservoirs fed from the depths
“In Greenland, this double ridge formed in a place where the water from the surface lakes and rivers drains into the near-surface area, where it collects and freezes again,” says Culberg. “One way similar water pockets could form in the ice of Europa is that water from the subglacial ocean is being pushed up through cracks in the ice crust,” he explains. Given the frequency of double-ridge structures on the moon’s surface, this would mean there are many such water pockets in the ice, the scientists say.
The study results thus contribute to the evidence that the ice sheet of Europe is shaped by geological and hydrological processes that enable dynamics and thus a possible exchange of substances. So far, this assumption has been supported primarily by evidence of ice geysers, from which water appears to be erupting from the depths in some places on the surface. As the researchers explain, evidence of the complexity and dynamic processes of Europa’s ice sheet are important for assessing the potential for life to evolve. Because they could facilitate the exchange between the subglacial ocean and the nutrients accumulated on the surface from neighboring celestial bodies.
Future missions to the moon could clarify whether the scientists are right in their assumptions about the cause of the double-ridge structures on Europa. Because ice-penetrating radar will be among the currently planned tools for exploring Europa from space. The results of the current study provide researchers with a radar signature that they can use to confirm or refute the possible process of double comb formation. “While we now present another explanation for the formation of the double ridges among the many previous ones, we can support it with observations of the formation of a similar feature on Earth. This opens up new possibilities for very exciting discoveries in the case of Europe,” says Culberg.
Source: Stanford University, professional article: Nature Communications, doi: 10.1038/s41467-022-29458-3