For some years now, the scientific community has focused its research on the south pole of Enceladus, Saturn’s most active moon, because of its geysers of steam and ice that sprout from fractures known as tiger stripes (due to its shape that resembles tiger stripes). These eruptions, detected for the first time by the Cassini mission in 2005, demonstrated that beneath its icy surface lies an ocean maintained by internal heat. This historic discovery pointed for the first time in the direction that this Saturnian satellite could harbor life. But a new study reveals that Enceladus’s north pole, which was believed to be inert, also holds a secret.
The research that undertook the task of deciphering this enigma analyzed data from the Composite Infrared Spectrometer (CIRS) collected by Cassini throughout its mission (2004-2017). The analysis showed that Enceladus’s north pole emits more heat than it should if it were only reflecting the weak light of the Sun or the brightness of Saturn. The results, published this week in the journal Science Advancesshow a difference of about 7 kelvin compared to the “passive” models (those that do not consider internal energy sources). To explain this difference, the researchers calculated an internal heat flux of about 46 milliwatts per square meter.
While that amount may seem small, it is equivalent to about 1.7 gigawatts of energy released beneath the northern surface, comparable to the power of a large nuclear reactor. It should be noted that it is less than the heat emitted by the south pole (between 4 and 19 gigawatts), but it represents an unexpected figure: it is the first evidence of endogenous heat outside the southern hemisphere of the moon.
“Enceladus is a key target in the search for life beyond Earth, and understanding the long-term availability of its energy is critical to determining whether it can support life,” said Dr. Georgina Miles, researcher at the South West Research Institute and visiting scientist at the Department of Physics at the University of Oxford, in a press release.
Detection was not easy. In the winter of 2005, when Cassini observed the dark North Pole, temperatures were around 30 kelvin (-243 °C). Under these conditions, any increase in energy produces a notable increase in temperature. Thanks to this sensitivity, scientists were able to identify subtle warming. After ruling out alternatives, they concluded that the most likely explanation was an internal heat contribution.
What is the origin of that internal heat?
Researchers estimate that the source of this energy remains the same as that which powers the southern geysers: tidal friction. As Enceladus orbits Saturn, its slight eccentricity causes the planet to constantly stretch and compress it, generating heat inside. The key is that this heat does not dissipate faster than it is produced. If the balance between warming and heat loss holds (as the new data suggest), Enceladus’s subglacial ocean could persist for millions of years.
The team calculates that, by adding the northern and southern flow, the total heat emitted by the moon does not exceed 54 gigawatts, a figure very close to estimates of the heat generated by the tides. This coincidence reinforces the idea that Enceladus is in a stable and long-lived state, which increases the likelihood that its ocean is habitable.
“Understanding how much heat Enceladus releases globally is crucial to knowing whether it can support life,” said Dr. Carly Howett, a researcher in the Department of Physics at the University of Oxford and the Planetary Science Institute in Tucson, Arizona. “It is truly exciting that this new result supports the long-term sustainability of Enceladus, a fundamental component for the development of life.”
