Warm ocean beneath Saturn’s icy moon Enceladus may be perfect for life

A team of scientists from Oxford University, the Southwest Research Institute, and the Planetary Science Institute in Tucson, Arizona, has uncovered the first evidence of significant heat flow at Enceladus' north pole. Until now, scientists believed that heat loss was limited to the south pole, where geysers shoot water vapor and ice particles into space. The new measurements confirm that Enceladus is far more thermally active than previously thought, indicating that it generates and releases much more heat than a dormant, frozen moon would.

A Hidden Ocean Beneath the Ice

Enceladus is a geologically active world with a global, salty ocean hidden beneath its icy surface. Scientists believe this ocean is the main source of the moon's internal heat. Because it contains liquid water, warmth, and essential chemical ingredients (such as phosphorus and complex hydrocarbons), this underground sea is considered one of the most promising environments in the solar system for life beyond Earth.

For life to thrive, Enceladus' ocean must remain stable over long periods, maintaining an equilibrium between energy gained and lost. This balance is sustained through tidal heating, caused by Saturn's powerful gravitational pull that stretches and compresses the moon as it orbits. If too little heat is produced, Enceladus' surface activity would fade, and its ocean could eventually freeze. Too much energy, however, might trigger excessive geological activity, disrupting the delicate environment that supports its ocean.

"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," explained Dr. Georgina Miles (Southwest Research Institute and Visiting Scientist at the Department of Physics, University of Oxford), the study's lead author.

Measuring Enceladus' Mysterious Warmth

Until recently, scientists had only measured heat loss at the moon's south pole. The north pole was believed to be geologically quiet and inactive. To challenge this assumption, the research team used data from NASA's Cassini spacecraft to study the north polar region during two key periods: the deep winter of 2005 and the summer of 2015. These observations allowed scientists to estimate how much energy Enceladus loses as heat moves from its relatively "warm" subsurface ocean (0°C, 32°F) through its icy crust to the surface, which remains bitterly cold (-223°C, -370°F), before escaping into space.

By modeling expected surface temperatures during the long polar night and comparing them with infrared data from Cassini's Composite InfraRed Spectrometer (CIRS), researchers found that the north pole's surface was roughly 7 K warmer than expected. The only explanation for this excess warmth is heat leaking upward from the hidden ocean.

The team measured a heat flow of 46 ± 4 milliwatts per square meter. While that may sound modest, it equals about two-thirds of the average heat escaping through Earth's continental crust. Across Enceladus, this amounts to about 35 gigawatts of energy -- roughly the power produced by 66 million solar panels (530 W each) or 10,500 wind turbines (3.4 MW each).

A Stable Ocean Beneath the Ice

When the new measurements are combined with the heat previously detected at the active south pole, Enceladus' total heat loss reaches about 54 gigawatts. This figure aligns closely with predictions of how much heat should be generated by tidal forces. The nearly perfect balance between heat creation and loss indicates that Enceladus' ocean could remain liquid for vast spans of time, offering a stable, long-term environment that might allow life to develop.

"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 study. "It is really exciting that this new result supports Enceladus' long-term sustainability, a crucial component for life to develop."

How Long Has the Ocean Existed?

The next challenge for scientists is to determine how long Enceladus' ocean has been around. If it has existed for billions of years, the conditions for life would have been stable long enough for it to potentially emerge. However, the exact age of the ocean remains uncertain.

Mapping Enceladus for Future Missions

The research also demonstrated that thermal readings can help estimate the thickness of Enceladus' ice shell, an important factor for planning future missions that may attempt to explore its ocean using robotic probes or landers. The analysis suggests that the ice is 20 to 23 km thick at the north pole, and about 25 to 28 km thick on average across the moon -- slightly deeper than earlier estimates derived from other models.

"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 the data might not reveal all its secrets until decades after it has been obtained."