A new analysis of surface temperature readings from NASA’s Cassini Mission has determined that Saturn’s moon Enceladus is losing heat from both poles.
The study, conducted by researchers from Oxford University, the Southwest Research Institute (SwRI), and the Planetary Science Institute (PSI), overturns previous assumptions that Enceladus was only losing heat from its active South Pole, thereby increasing the odds that the icy moon could support biological activity.
“This stability means Enceladus’ ocean could have existed for a long-term, potentially giving life a chance to have evolved,” explained the study’s lead author, Dr Georgina Miles from SwRI and Visiting Scientist at the Department of Physics, University of Oxford, and study co-author, Oxford Prof. Carly Howett, also from the PRI, in an email to The Debrief.
The research team behind the new analysis also described Enceladus as “a top contender for extra-terrestrial life,” because it has heat, liquid water, and the right chemicals, such as complex hydrocarbons and phosphorus, needed for life on Earth. The researchers also told The Debrief that future missions to Enceladus could reveal critical data about the moon’s age and the age of its subsurface ocean, which is necessary to confirm its potential habitability.
Although researchers have suspected for some time that Enceladus’ ocean might support life, its long-term stability, which is required for life to evolve, has remained in question. This stability can only exist if its energy losses and gains remain in balance.
For example, if the moon’s squeezing and stretching caused by Saturn’s gravity creates too little energy, the surface activity would slow or even stop, resulting in the sub-surface ocean freezing. Conversely, if this gravity-induced tidal activity generates too much heat, the ocean’s activity would increase, which the researchers note would also dramatically alter its environment.
To determine if the ocean could stay stable over the geological timescales needed for life to develop, the researchers examined surface temperature data captured by Cassini between 2005 and 2017.
“We used north polar late winter observations (when the north pole was in winter darkness) and summer observations permanent daylight) for this study,” Dr. Miles and Prof. Howett told The Debrief.
The researchers said using data captured by Cassini during the moon’s deep winter (2005) and deep summer (2015) was important because heat conducted through the surface ice shell during the winter might be mistaken for the pole still cooling down from the summer. However, they note, this “wouldn’t be the case” for observations collected in summer.
“Observations from both seasons were required to rule that out,” they explained, adding that warmer regions were “easier to spot” when the moon’s surface is at its coldest.
According to a statement detailing the research, the team used this data to create expected surface temperature models during the polar night and compare them against infrared observations captured by Cassini’s Composite InfraRed Spectrometer (CIRS). These models revealed that the surface of the North Pole, which had previously been considered inactive, was approximately seven times warmer than previous models had predicted. The team said this discrepancy could only be explained if the sub-surface ocean was leaking heat through the icy shell.
Dr. Miles and Prof. Howett told The Debrief that the moon’s maximum total outgoing heat “is comparable to the best current estimates” of Enceladus’ tidal heating rate. In short, the heat generated and lost are a close match. The team said this finding indicates it might be possible for the sub-surface ocean to be maintained in liquid form “so long as its orbit around Saturn remains stable.”
“With current theories about ‘tidal locking,’ this is entirely possible,” they added.
In the study’s conclusion, the researchers suggest that a better understanding of Enceladus’ age would help constrain the duration of its subsurface ocean’s likely existence in liquid form. Dr. Miles and Prof. Howett told The Debrief that the age of all of Saturn’s moons is “highly uncertain,” and noted that Enceladus “is particularly difficult to age” because it has been continually resurfaced by alternating heating and cooling episodes throughout its icy shell.
“The fate of the moon is tied to the evolution of Saturn and its interior structure,” they said, adding that “Enceladus could be up to 1 billion years old, or as young as 150 million years, with current best estimates of 200-450 million years old.” For comparison, the Earth is approximately 4.5 billion years old.
When asked about any potential experiments that could help confirm the habitability of Enceladus’ ocean, the researchers said one viable method would involve in situ measurements of the size and composition of the nanoparticles previously observed by Cassini in the plumes ejected into space from the moon’s south pole. These readings could be used to “provide limits” on how long they’ve been at the rock-ocean interface, they explained, while also noting that “a lot of laboratory work is needed to verify this too.”
When discussing what tools or missions are necessary to confirm the moon’s potential habitability, the team said their work directly highlighted the need for long-term missions to ocean worlds like Enceladus that may harbor life, “and the fact [that] the data might not reveal all its secrets until decades after it has been obtained.”
“Our estimates of the energy balance will be significantly improved by future missions to Enceladus,” Dr. Miles and Prof. Howett told The Debrief.
Only one mission is currently selected to return to Enceladus, the European Space Agency’s next Large Class L4 mission. However, they said several more missions “are in the proposal stage.”
“The best information comes from Enceladus’ polar regions, which are hard to view from Earth-based observing systems,” the researchers told The Debrief. “You really need to return there to observe Enceladus with a modern instruments suite to understand its habitability potential.”
The study “Endogenic heat at Enceladus’ north pole” was published in Science Advances.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.