How we think hydrothermal activity works on Enceladus, based on data from the NASA/ESA Cassini-Huygens mission. Credit: ESA
Cassini’s new analysis shows Saturn’s moon Enceladus leaking heat from both poles, not just the south.
This balanced heat flow suggests its underground ocean could stay liquid for geological ages, supporting conditions for life. Scientists even used temperature data to estimate ice thickness, preparing the way for future missions to probe its mysterious depths.
Heat From Both Poles – A Game Changer
A study released today (November 7) in Science Advances, led by scientists from Oxford University, the Southwest Research Institute, and the Planetary Science Institute in Tucson, Arizona, has revealed the first clear evidence of strong heat flow at Enceladus’ north pole. This discovery overturns earlier beliefs that heat loss occurred only in the moon’s active south pole. The results show that Enceladus gives off far more heat than expected from a frozen, inactive world, reinforcing the idea that it has the energy needed to sustain life.
Enceladus is an exceptionally dynamic moon with a global, salty ocean beneath its icy surface. Scientists believe this subsurface ocean is the source of the moon’s heat. Because it contains liquid water, warmth, and essential chemicals (such as phosphorus and complex hydrocarbons), this hidden sea is considered one of the most promising environments in our solar system for life beyond Earth.
However, for life to persist, Enceladus’ ocean must stay stable, maintaining a balance between heat gained and heat lost. This equilibrium depends on tidal heating: Saturn’s immense gravity flexes the moon during each orbit, producing internal friction and heat. If the tidal energy weakens, the ocean could gradually freeze. If it becomes too strong, increased activity might disrupt the delicate conditions that allow the ocean to exist.
A new study has constrained Enceladus’ global conductive heat flow by studying its seasonal temperature variations at its north pole (yellow). These results, when combined with existing ones of its highly active south polar region (red), provide the first observational constraint of Enceladus’ energy loss budget (<54 GW) – which is consistent with the predicted energy input (50 to 55 GW) from tidal heating. This implies that Enceladus’ current activity is sustainable in the long term—an important prerequisite for the evolution of life, which is thought to exist in its global subsurface ocean. Credit: University of Oxford/NASA/JPL-CalTech/Space Science Institute (PIA19656 and PIA11141)
Why Heat Flow Matters for Alien Life
“Enceladus is a key target in the search for life outside the Earth, and understanding the long-term availability of its energy is key to determining whether it can support life,” said Dr. Georgina Miles (Southwest Research Institute and Visiting Scientist at the Department of Physics, University of Oxford), lead author of the paper.
Until now, scientists had directly measured heat loss only at Enceladus’ south pole, where geysers of water vapor and ice erupt from deep surface cracks. The north pole, in contrast, was thought to be quiet and geologically frozen.
How Cassini Measured the Moon’s Hidden Warmth
To test that assumption, researchers analyzed data collected by NASA’s Cassini spacecraft during two key periods: the frigid north polar winter of 2005 and the summer of 2015. By comparing these infrared observations, the team calculated how much energy the moon releases as heat from its “warm” (0°C, 32°F) subsurface ocean through its ice shell to the surface, which sits at an icy (–223°C, –370°F), before radiating out into space.
When the researchers modeled how cold the surface should have been in polar night and compared it with readings from Cassini’s Composite InfraRed Spectrometer (CIRS), they found the north polar surface to be about 7 K warmer than expected. This subtle excess warmth can only be explained by heat rising from the ocean below. Although the detected heat flow (46 ± 4 milliwatts per square meter) may sound modest, it equals roughly two-thirds of the average heat escaping through Earth’s continental crust. Spread across the entire moon, that amounts to roughly 35 gigawatts of energy—comparable to the combined output of about 66 million solar panels (530 W each) or 10,500 wind turbines (3.4 MW each).
Adding the heat already known to escape from the active south pole raises Enceladus’ total heat output to about 54 gigawatts. This total matches predictions of tidal heating, implying the moon’s interior heat input and loss are in balance. Such thermal stability could allow Enceladus’ ocean to remain liquid for immense spans of time, creating steady conditions where life might arise.
Sustainability for Life Across Millennia
“Understanding how much heat Enceladus is losing on a global level is crucial to knowing whether it can support life,” said Dr. Carly Howett (Department of Physics, University of Oxford and Planetary Science Institute in Tucson, Arizona), corresponding author of the paper. “It is really exciting that this new result supports Enceladus’ long-term sustainability, a crucial component for life to develop.”
The team’s next challenge is to determine how long the moon’s ocean has persisted. Although it appears stable today, its true age—and therefore the length of time life could have had to emerge—remains uncertain.
Mapping the Icy Shell for Future Missions
The research also showed that thermal data can help estimate the thickness of Enceladus’ icy crust, a key factor for future missions that may drill or dive into its ocean. Based on these measurements, the ice is estimated to be 20 to 23 km thick at the north pole and about 25 to 28 km thick on average across the globe—slightly deeper than previous estimates derived from other remote-sensing and modeling methods.
“Eking out the subtle surface temperature variations caused by Enceladus’ conductive heat flow from its daily and seasonal temperature changes was a challenge, and was only made possible by Cassini’s extended missions,” added Dr. Miles. “Our study highlights the need for long-term missions to ocean worlds that may harbor life, and the fact that the data might not reveal all its secrets until decades after it has been obtained.”
Reference: “Endogenic heat at Enceladus’ north pole” by Georgina Miles, Carly J. A. Howett, Francis Nimmo and Douglas J. Hemingway, 7 November 2025, Science Advances.
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