Saturn’s moon Enceladus is already known as one of the most intriguing places in our solar system, and now new findings from the Cassini spacecraft have been published, which will only add to our fascination with this little world.
Before Cassini, Enceladus was expected to be little more than a frozen ball of ice and rock, being so distant from the sun. But this moon held surprises, the kind which would make Enceladus a much more interesting place, and a new prime target in the search for possible life elsewhere in the solar system.
In 2005, Cassini made its first discovery of something amazing – water vapor geysers spewing out from the surface. Geysers? How could there be something like that on this tiny cold moon? But there they were; since then many images have been taken and Cassini has even passed directly through some of them, sampling the spray as it did so. The plumes contained water vapor, ice particles, salts and organics. They were found to originate from deep fissures called “tiger stripes” at the south pole of the moon, which were warmer than the surrounding icy terrain. So what did this mean? Could there be water somewhere below the surface, like on Jupiter’s moon Europa? The new results presented today support that incredible idea – the fissures allow water from a subsurface sea to make its way to the surface, when then explodes out into space as huge plumes of water vapor which then freeze into ice particles.
The new findings are the result of the previous seven years of study of the geysers; Cassini scientists have now produced a detailed map of the known geysers, all 101 of them! They have been published in two new papers in the online edition of The Astronomical Journal (abstract/download here).
“Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa,” said Carolyn Porco, leader of the Cassini imaging team from the Space Science Institute in Boulder, Colorado. “It also told us the geysers are not a near-surface phenomenon, but have much deeper roots,” she added. She is also the lead author of the first paper.
Mapping the locations of the plumes helped scientists to better pinpoint where they originate, which, as theorized, turned out to be below the outer icy crust of Enceladus. Pathways through the ice (the fissures) should be able to remain open, allowing liquid water from deeper inside the moon to escape to the surface. By analyzing the gravity data from Cassini, it was determined that the source of the plumes must be the subsurface sea.
Using the triangulation method, similar to that used on Earth to survey geological features, the Cassini team found that the greatest geyser activity conceded with the location of the “hot spots” in the tiger stripes. By comparing those results with high-resolution data first collected in 2010, the scientists were able to pinpoint the locations of individual geysers, which coincided with very small hot spots, only a few dozen feet, or tens of meters, across. That’s too small for frictional heating, but just the right size if water vapor is condensing on the near-surface walls of the fissures (tiger stripes).
In addition, it was found that the opening and closing of the fissures, due to the gravitational pull as Enceladus orbits Saturn, matched the brightness variations in the plumes, as expected if they were due to tidal flexing and tides in the water below. This tidal flexing, however, doesn’t predict when a plume will begin to brighten; some other as-yet unknown process must be at work.
This information, plus the fact the organics have already been found in the plumes, raises the obvious question: could there be life of some kind in those waters deep below the surface? We know that on Earth, even in the deepest, coldest and darkest waters, life thrives. The ingredients for life (as we know it, anyway) all seem to be there: water, heat, organics and chemical nutrients (where the bottom of the sea is thought to be in contact with the rocky core, like Earth’s oceans in contact with the rocky mantle). Answering that question will require follow-up missions beyond Cassini. In the meantime however, we have valuable clues that maybe, just maybe, there is something swimming in those alien waters, even if just simple microorganisms.
See also this excellent summary of these findings on the CICLOPS website. As Carolyn Porco so eloquently summarizes:
“As we contemplate the approaching end of Cassini’s travels around Saturn, we dream of the day, hopefully not far in the future, when we can return to Enceladus to answer the question now uppermost in the mind: Could a second genesis of life have taken hold on this small icy moon of a hundred and one geysers? For we now know this: if life is indeed there, it is there for the taking.”
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