In this blog post, we examine the debate within the scientific community by exploring various possibilities—such as tidal heating and radioactive energy—to determine whether the subglacial ocean believed to exist on Jupiter’s moon Europa could indeed serve as a cradle of life.
The debate over the possibility of life on Jupiter’s moon Europa is heating up again. This is because there is a fierce standoff between the claim that Europa harbors a vast ocean capable of supporting life and the counterargument that, due to the absence of energy and oxygen cycles, it is essentially just a “dead ocean.” Amid this debate, the controversy is expanding further following 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 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 the extreme environment—characterized by intense radiation and average temperatures of minus 170 degrees—makes it seem inhospitable to life, it is estimated that a vast ocean exists beneath a thick layer of ice, extending to depths ranging from tens to over 100 kilometers. This ocean is sustained even in an environment where sunlight barely reaches it, a phenomenon made possible by 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, in which the planet’s internal rock and ice are repeatedly stretched and compressed. The frictional heat generated by this process melts the ice, sustaining the liquid ocean. The core of this optimistic view is that such an environment could create conditions similar to those found in Earth’s deep-sea hydrothermal vents, and if chemicals such as hydrogen sulfide or methane are supplied, the foundation for microbial life could be established. Furthermore, the ice on Europa’s surface can interact with Jupiter’s strong magnetic field to produce oxidizing agents such as oxygen or hydrogen peroxide; if these substances sink into the ocean and combine with hydrogen, energy can be generated 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, similar to Earth’s deep seas—are absolutely necessary. If tidal heating is insufficient and the mantle has already cooled, Europa’s ocean may be nothing more than a cold, stagnant mass of water. Furthermore, it has been suggested that Europa’s thick ice crust may be blocking the movement of oxygen. In fact, according to observations by the Juno spacecraft, the thickness of Europa’s ice crust is estimated to be tens of kilometers; 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 would inevitably be 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 entire ocean. In other words, even if there were no hot oceans or hydrothermal vents, the rock beneath Europa’s surface could itself serve as a massive energy source.
However, all of these hypotheses remain purely theoretical, 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 its 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 a past asteroid impact melting the ice, followed by the saltwater lake formed beneath it refreezing and rising to the surface. This phenomenon is considered a key clue indicating the presence of liquid water inside Europa and, at the same time, suggests the possibility that the surface and the internal ocean are connected.
Ultimately, Europa remains a subject of scientific inquiry, leaving behind countless questions. It is not yet clear whether it is an environment capable of supporting life or a world frozen in time, cut off from energy sources amid 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.
