Plumes of steam that erupt from the surface of Saturn’s icy moon Enceladus may not actually prove the existence of an underground ocean. Most theories indicate these oceans do exist, but a new study proposes an alternate cause for the notorious plumes.
BACKGROUND: PLUMES FIRST SPOTTED BY CASSINI IN 2005
NASA astronomers first imaged the plumes in 2005, when their Cassini probe flew by and spotted them erupting from the moon’s south pole. Closer analysis showed that these plumes contained water in the form of tiny ice crystals.
Since that discovery, a number of follow-up missions have been proposed, with some even hoping to fly a probe directly through the plumes and capture a sample of the water crystals for closer analysis. If these plumes are made up of sea water from the subsurface ocean most researchers think lies below the moon’s icy outer shell, then they could potentially contain microscopic life forms that some astrobiologists say might inhabit these oceans.
Now, a team of researchers is using sea ice modelling software to determine if these plumes do come from these possible oceans, or if there may be another mechanism at work.
ANALYSIS: OCEANS STILL LIKELY, BUT THEY MAY NOT CAUSE THE PLUMES
Presented at the American Geophysical Union’s 2021 fall meeting, researchers at Dartmouth College and led by physicist Colin Meyer used simulation software designed to examine the behavior of sea ice on here on earth. When they plugged a model for Enceladus into the software and ran simulations, the results indicated that there may indeed be oceans under the moon’s crust, but there may also be a middle zone of “slushy” material that exists between the crust and these potential oceans. If true, they say, the plumes we see erupting over the moon’s south pole may actually originate from these pools and not the deeper subsurface ocean.
“Maybe we didn’t get the straw all the way through the ice shell to the ocean,” said planetary scientist and co-presenter Jacob Buffo of Dartmouth College at the December 15th meeting. “Maybe we’re just getting this weird pocket.”
If Meyer, Buffo and their fellow colleagues’ simulations are correct, and these pockets of water are the real source of the plumes and not the prposed oceans, it could be a huge blow to future missions who had hoped to sample those oceans without having to drill through the hard outer crust.
“You could be sampling this slushy region in the middle of the shell,” said Buffo, “and that might not be the same chemistry as is down in the ocean.”
OUTLOOK: MORE CASSINI PLUME DATA MAY OFFER ANSWERS
As of January 2022, there are no missions officially on the books to return to Enceladus, although many are under consideration. However, Cassini didn’t even take its final readings of Enceladus until October of 2015, a full year after its arrival, which according to NASA’s mission page, means that “explorers will be poring over the data it sent home for years to come, planning for the day we return to delve deeper into its secrets.”
“As we continue to learn more about Enceladus, and compare data from different instruments, we are finding more and more evidence for a habitable ocean world,” said Cassini Project Scientist Linda Spilker. “If life is eventually discovered in Enceladus’ ocean by a mission after Cassini, then our Enceladus discoveries will have been among the top discoveries for all planetary missions.”