For decades, Europa, one of Jupiter's largest moons, has been considered one of the star candidates in the search for life beyond EarthBeneath its icy surface lies a vast underground ocean of salt water that, on paper, seemed to possess several basic ingredients for habitability.
However, a number of recent works, spearheaded by a study published in Nature Communications.They paint a much colder picture, in every sense. Internal models suggest that the seabed of this ocean would be too rigid and geologically dull as to provide the energy and nutrients that even the most resilient microbes need.
A vast ocean that does not guarantee life
Beneath Europa's icy crust lies a global ocean that, according to the most widely accepted estimates, could reach between 60 and 150 kilometers deepAll of this covered by a layer of ice about 15 to 25 kilometers thick, very fractured on the surface but, apparently, resting on a surprisingly calm bottom.
Although its diameter is around 3.100 kilometers —somewhat smaller than that of our Moon—, calculations indicate that this ocean of salt water could to contain more water than all of Earth's oceans combinedThat figure alone fueled for years the idea that Europa was one of the most promising places in the solar system to find life.
The new study, led by planetary scientist Paul ByrneA researcher from Washington University in St. Louis challenges that optimistic view. After reconstructing the moon's interior using physical models and comparing its properties with those of the moon, he found that the moon's interior was indeed the most realistic. Earth, the Moon and Io (another extremely volcanic Jovian moon), the team concludes that Europa's bedrock would be mechanically very resistant, to the point of preventing the formation of large tectonic structures.
According to the authors, nothing would be expected on that ocean floor long mid-ocean ridges, deep trenches, underwater volcanoes, or active hydrothermal ventsIn practice, we would be facing a world with an immense ocean, but settled on an almost immutable rocky ground.
Why the ocean floor is key to habitability
On Earth, many of the hypotheses about the origin of life point to the hydrothermal jets of the seabedThere, the interaction between hot rock and seawater, driven by plate tectonics and volcanism, generates chemical compounds such as methane and abundant energy available to microorganisms.
Byrne's team transferred this knowledge to Europa to investigate whether similar processes might exist on that moon. Their conclusion is that the European seabed would be too rigid as to fracture and renew themselves in a sustained manner, which would prevent the reproduction of the type of dynamic environments that we know in the Earth's ocean floors.
In Byrne's own words, if we could send a robotic submarine to the ocean of Europe, we most likely would not find recent fractures, active volcanoes, or hot water columns rising from the bottom. Geologically, everything would point to a landscape dominated by calm, without the sources of chemical energy that feed the deep ecosystems in the Earth.
This view coincides with other studies that indicate that water-rock reactions In Europe, these ecosystems would be limited to the first few hundred meters of the seabed, without intense and continuous exchange between the rocky interior and the ocean. Such a scenario greatly reduces the likelihood of complex ecosystems forming and being maintained.
Even so, the study does not completely rule out the possibility that they could exist. very simple microorganisms in specific niches, but the amount of energy available would, according to the models, be very limited to sustain large communities.
The influence (and limits) of Jupiter's gravity
One of the great internal engines of Jovian moons is the tidal warming, the same process that, taken to the extreme, turns into Io on the most volcanically active body in the solar system. Jupiter's intense gravity constantly deforms this moon, generating internal heat and fueling its spectacular volcanism.
In the case of Europe, the situation is different. Its orbit is more stable and somewhat further awayso that tidal forces are weaker. The models in the new study indicate that this warming has been sufficient to to prevent the ocean from freezing completelybut it is not enough to deform the bedrock with the intensity needed to activate robust tectonics or prolonged volcanism.
The researchers also point out that the original internal heat of the rock core It would have largely dissipated billions of years ago. This thermal depletion would explain why the current ocean floor appears as such a stable and relatively undynamic environment.
This combination of moderate tides And the cooled core leaves Europa in a sort of intermediate zone: it retains a liquid ocean under the ice, but lacks the geological machinery that, on Earth, is considered fundamental to sustaining deep ecosystems.
The image contrasts with other icy worlds, such as Titan (Saturn), where some models continue to suggest a possibly more active interior with a very different chemistry, leading some in the European and American scientific community to to distribute the focus of the search for life among several candidates and not only in Europe.
Three requirements for life… with one big unknown
In astrobiology, three major conditions for life as we know it are often emphasized: Liquid water, organic compounds, and a source of energyOn paper, Europe fulfills the first two requirements well and, at least partially, the third.
On the one hand, all missions and observations agree that the moon harbors a global ocean of liquid waterOn the other hand, the following have been identified on its icy surface: organic molecules which, quite likely, would also be present in the underground ocean.
The issue is energy. Europa's orbit around Jupiter generates tidal warming inside, but models suggest that this contribution would be weak on the seabed. That is, there would be enough energy to prevent the water from freezing completely, but not enough to stimulate a active tectonics or sustained volcanism at the rocky base.
This nuance radically changes the interpretation of habitability. Having water and organic matter is necessary, but without a geological engine that mixes materials, renews the crust, and facilitates continuous chemical reactions, the probability of life arising and being maintained It is reduced to a minimum.
The authors of the paper insist that their results refer to the Actual state from Europe. They do not rule out that, in the past, the interior of the moon could have been much more active, with a warmer seabed and hydrothermal vents capable of sustaining ecosystems for a limited time.
Could Europe have been more habitable in the past?
One of the most intriguing points of the study is the idea that Europe may have been, billions of years ago, a much more active and potentially habitable worldIn that early phase, residual heat from the core and perhaps more intense tides could have fueled a seabed with hydrothermal vents and vigorous fluid circulation.
In that scenario, it cannot be ruled out that they might appear ecosystems based on water and rock chemistrysimilar to those observed at Earth's mid-ocean ridges. Over time, however, the progressive loss of internal heat would have extinguished this activity, leaving the seabed in the stillness suggested by current models.
If something like that happened, any potential European biosphere would have had a limited period of time to develop and adapt to the decrease in available energy. Determining whether that margin was sufficient for life to emerge, and whether that life could survive in an increasingly colder world, is one of the great unknowns that upcoming missions will try to answer.
This temporal perspective also affects how the biomarker search on the icy surface. Some of the observed structures, such as chaotic terrain or areas where the ice appears to have been fractured and reorganized, could hold clues about a possible past exchange between the ocean and the upper layer.
This debate is being closely followed in Europe and other research centers on the continent, as it influences future planning. European missions and collaborations with NASA when prioritizing scientific objectives and selecting instruments.
Europa Clipper, JUICE and Europe's role in space exploration
Although the new research lowers expectations of finding life on Europa, scientific interest in this moon has not waned, far from it. On the contrary, missions like Europa Clipper (NASA) and JUICE (European Space Agency) have this frozen world among their priority objectives.
Europa Clipper, launched by NASA and scheduled to fly by the moon starting in 2031It will make dozens of close passes to obtain high resolution images The mission aims to measure the thickness of the ice crust and characterize the subsurface ocean in detail. Its instrumentation will include ice-penetrating radar, magnetometers, and spectrometers capable of analyzing the chemical composition of the surface and any water plumes.
For its part, the mission JUICE The ESA's Jupiter ICy Moons Explorer is already on its way to the Jovian system and is expected to arrive early next decade. Although its primary target will be the moon Ganymede, the probe will also study Europe and Callistoproviding a very valuable overview of Jupiter's icy moons.
From a European perspective, these missions represent a strategic opportunity to consolidate the role of the continent's space industry and its research centers exploring the outer solar system. Spain, through its participation in the ESA and its high-tech companies, is also part of this commitment to better understand the icy worlds.
The data provided by Europa Clipper and JUICE will be essential to verifying the extent to which current models accurately describe a inert ocean floor Or if, on the contrary, there are still surprises to be discovered under the ice.
The image that is emerging is that of a moon with Lots of water but little internal energywhere the immense ocean hidden beneath the ice would likely be a cold and chemically inactive environment. Europa remains a privileged natural laboratory for studying how icy worlds function and what they truly need to be habitable, although each new piece of data suggests that, at least for now, the Jupiter's moon has no life Or, if it did have one, that stage is long behind it in its history.
