The universe is full of icy worlds that scientists suspect could serve as homes for extraterrestrial life. These celestial bodies are so cold that humans could never enter them without freezing to death. However, if they have liquid water and carbon, they could facilitate the development of organic life like the inhabitants of our own planet. These worlds would not only have to contain organic chemicals, but also be stable enough for life to realistically exist there. That's why astrobiologists are increasingly turning their attention to icy celestial bodies such as Jupiter's moons Europa and Ganymede, Saturn's moons Titan and Enceladus, Uranus' moon Miranda and the dwarf planet Ceres.
How could life survive in such a cold, hostile environment? We have found plenty of ice in our solar system, but no moon or planetary surface other than Earth is known to have consistent liquid water. However, there are many theories that there could be subsurface oceans, which is why NASA launched the Europa Clipper last October, which will search for signs of life on Jupiter's moon when it arrives in 2030. Meanwhile, scientists are still puzzling over the physics behind such an icy ocean that could harbor life.
Researchers at Texas A&M University and the University of Washington, Seattle, recently published a study in the journal Nature Communications in which they propose a new concept: “cenotectics,” or the absolute lowest temperature at which a liquid can be exposed to different temperatures Pressures and concentrations remain stable. The term comes from Greek and means “universal melting”. By applying cenotectic physics to known conditions on various distant worlds, the researchers determined how water on these icy distant bodies can remain liquid enough to support life.
“Europe contains twice as much liquid water as all of the Earth’s oceans combined.”
“This low-temperature boundary, called cenotectics, helps us constrain the conditions under which liquid water – often considered a prerequisite for habitability – could exist on distant worlds,” said study co-author Matthew Powell-Palm Assistant professor of mechanical engineering at Texas A&M, Salon said.
These limits usually include the fact that water is frozen and can therefore no longer support life; Cenotectics takes into account thermodynamic forces such as pressure and chemical activity that can keep water in its liquid state despite the extremely low temperatures found on icy worlds.
According to the study authors, “Cenotectics plays a central role in the 'endgame' of planetary oceans. As large water-rich planetary bodies cool over geological timescales or internal heating such as tidal dissipation or radiogenic heating is lost, their oceans will also cool.” They freeze gradually from top to bottom until complete solidification is achieved. This effect is particularly interesting for large icy moons such as Ganymede, Callisto and Titan, but also for cold ocean exoplanets such as Trappist 1e-g and water-rich rogue exoplanets.
The authors speculate in their paper about the “intriguing applications” of the cenotectic concept in planetary science, particularly for “icy worlds such as Europa, Enceladus, Titan, Ganymede, Ceres, Pluto and possibly the moons of Uranus Ariel, Umbriel, Titania and.” Oberon.” For example, “by measuring the cenotectics of various water-salt solutions, we can determine some of the chemistry of the oceans “To capture Europe, determine the lowest temperature at which these solutions remain liquid and the corresponding pressure and salt concentrations required for that liquidity,” Powell-Palm said. “Thus, by conceptualizing and measuring cenotectics, we can narrow down the most extreme temperature-pressure conditions under which liquid water could exist” and link these to other possible variables such as gravity or the depth of the liquid beneath a world's icy and crusty surface .
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As another co-author explained to Salon, some of these places contain so much water that astrobiologists need a tool to figure out where and how these worlds contain liquid water on which organic molecules can transform into organisms.
“One of the most significant discoveries in planetary science and astrophysics of the last decade was the realization that icy moons contain the largest reservoir of liquid water in our solar system,” said Baptiste Journaux, research professor of earth and space sciences at the University of Washington – Seattle, said. “For example, Europe contains twice as much liquid water as all of Earth's oceans combined, while Titan and Ganymede each likely contain more than ten times more liquid water. “In addition, oceanic exoplanets are believed to have the largest reservoir of liquid water in the entire universe.”
Horizon of the icy moon Europa (Getty Images/Stocktrek Images)“These icy moons are our most promising targets for exploring the possibility of habitability, surpassing, in my opinion, even Mars,” Journaux added. He hopes future scientists will be able to use their research after obtaining data from Europa, Ganymede and Titan as part of upcoming exploration missions such as NASA's Europa Clipper, ESA's Juice and NASA's Dragonfly. Until this happens, Earth-based scientists will need to continue elaborating the theoretical framework behind cenotectics.
“Although we think the cenotectic concept and our first measurements are very exciting, we have only scratched the tip of the iceberg,” said Powell-Palm, apologizing for the pun. “In this study, we measure this cenotectic limit for simple aqueous chemicals (water + a salt), but more complicated solutions with many different salts (not to mention organic compounds that may be present) may behave differently and may better represent the chemical complexity of the oceans icy worlds.”
Scientists also need to learn about the numerous new hydrate materials (solid compounds that include both salt molecules and water molecules bonded together) found on these alien worlds, as researchers have encountered many during their own study.
“The role of these materials in dictating the limits of fluid stability further complicates the story, and the very existence of these materials shows us that there is still a lot of exciting exploration to be done in the area of low-temperature, high-pressure parameters relevant to icy worlds “We have in front of us,” said Powell-Palm.
As this new information arrives, Journaux is excited about the possibilities of applying the concept of cenotectics to help people discover life.
“This is where the groundbreaking discovery and definition of cenotectics play a crucial role,” said Journaux. “By setting an absolute limit on the existence of liquid water, even at high pressure and high salinity, cenotectic research allows us to set an absolute limit on the existence of oceans and potentially habitable environments.”