In this blog post, we examine the scientific debate surrounding whether the subsurface ocean believed to exist on Jupiter’s moon Europa could indeed serve as a cradle of life, exploring various possibilities such as tidal heating and radioactive energy.
The debate over the possibility of life on Jupiter’s moon Europa is heating up again. This is because arguments that Europa harbors a vast ocean capable of supporting life are locked in a fierce standoff with counterarguments claiming it is essentially a “dead ocean” due to the absence of energy and oxygen circulation. Amid this debate, the controversy is expanding further with the presentation of new research suggesting that radioactive energy emitted from Europa’s rocks could sustain an ecosystem. Meanwhile, NASA’s “Europa Clipper” probe, launched in 2024, is currently en route to reach Jupiter’s orbit in 2030 and is expected to provide decisive clues to this debate.
Europa is considered one of the most likely places in the solar system to harbor life. Although it appears inhospitable to life due to intense radiation and extreme temperatures averaging minus 170 degrees Celsius, it is estimated that a vast ocean exists beneath a thick layer of ice, extending to depths of tens to over 100 kilometers. This ocean remains stable even in an environment where sunlight barely reaches it, a phenomenon attributed to Jupiter’s powerful gravity. Europa follows an elliptical orbit, repeatedly moving closer to and farther from Jupiter. During this process, a phenomenon known as “tidal heating” occurs, causing the planet’s internal rock and ice to repeatedly expand and contract. The frictional heat generated by this process melts the ice, maintaining a liquid ocean. The core of the optimistic view is that this environment can create conditions similar to those found in Earth’s deep-sea hydrothermal vents, and if chemicals such as hydrogen sulfide or methane are supplied, a foundation for microbial survival could be established. Furthermore, the ice on Europa’s surface interacts with Jupiter’s strong magnetic field to generate oxidizing agents such as oxygen or hydrogen peroxide. If these substances sink into the ocean and combine with hydrogen, energy can be produced even without sunlight.
However, there is no shortage of skepticism regarding these hypotheses. Some argue that for life to exist in Europa’s ocean, hydrothermal vents—where hot water erupts from the seafloor, much like in Earth’s deep oceans—are absolutely necessary. If tidal heating is insufficient and the mantle has already cooled, Europa’s ocean could be nothing more than a cold, stagnant mass of water. Furthermore, it has been suggested that Europa’s thick icy crust may be blocking the movement of oxygen. In fact, according to observations by the Juno spacecraft, Europa’s icy crust is estimated to be tens of kilometers thick; in this case, oxygen generated at the surface cannot reach the ocean, making it difficult for the chemical reactions necessary to sustain life to occur. Ultimately, without a simultaneous supply of both an energy source and an oxidizing agent, the conditions necessary for life to exist are inevitably greatly weakened.
A new explanation that has emerged in response to this pessimism is the “radioactive energy” hypothesis. The rocks on Europa’s seafloor contain radioactive isotopes such as uranium, thorium, and potassium, which decay over billions of years, emitting heat and radiation. The theory posits that the radiation released during this process breaks down water molecules to produce hydrogen and oxygen compounds, which can serve as an energy source for microorganisms. According to the research team, the energy generated in this way is sufficient to sustain a substantial microbial ecosystem throughout Europa’s ocean. In other words, even if there are no hot seas or hydrothermal vents, Europa’s internal rocks themselves could act as a massive energy supply system.
However, all these hypotheses remain at the theoretical stage, and the existence of life on Europa has not yet been confirmed. The mission designed to verify this directly is the Europa Clipper. This spacecraft aims to measure the thickness of Europa’s ice and analyze plumes of water vapor erupting from the surface to search for traces of organic matter or life. Recently, attention has shifted to a unique terrain on Europa’s surface that spreads out like a spiderweb. This structure is interpreted as the result of heat generated by past asteroid impacts melting the ice, followed by the saltwater lakes formed beneath refreezing and rising to the surface. This phenomenon is considered a key clue indicating the presence of liquid water inside Europa, and it also suggests the possibility that the surface and the internal ocean are connected.
Ultimately, Europa remains a subject of scientific inquiry, leaving behind countless unanswered questions. It is not yet clear whether the environment is capable of supporting life or if it is a world frozen in time, cut off from energy sources under extreme conditions. However, one thing is certain: Europa is one of the most important keys to exploring the possibility of life in the solar system. Depending on the results of future explorations, we may be able to take another step closer to answering humanity’s long-standing question about life beyond Earth.
