“Something is going on on Enceladus – it’s active and we want to know,” said astrophysicist and curator at California’s Griffith Observatory, Laura Danly. That “something” turned out to be plumes of water vapor and ice particles erupting hundreds of miles into space from the ocean through cracks in Enceladus’s ice-encased surface — detected by the NASA’s Cassini spacecraft prior to the spacecraft’s fiery death-plunge into Saturn in 2017. The plumes provide a tantalizing glimpse into what the moon’s subsurface ocean might harbor –likely heated and churned by hydrothermal vents like those on Earth’s ocean floors.
Cassini Mission Data
In 2019,Cassini mission data to Saturn observed surface fissures on Enceladus perpetually erupting with water ice from its global subsurface ocean that appear as parallel, evenly spaced “stripes” some 130 kilometers long and 35 kilometers apart that are the launch pads for the moon’s dramatic geysers, which spew water and organic material from Enceladus’ subsurface ocean out into the void. Saturn’s icy moon is one of the most promising abodes for alien life in the solar system. In addition to the subsurface ocean and geological activity, the moon likely has an energy source that organisms could thrive in similar to those that sustain life at Earth’s hydrothermal vents.
The Towering Plumes
The data from the Cassini mission revealed organic building blocks in the Enceladus’ towering plumes that are potential precursors for amino acids and other ingredients required for life on Earth. “If the conditions are right, these molecules coming from the deep ocean of Enceladus could be on the same reaction pathway as we see here on Earth. We don’t yet know if amino acids are needed for life beyond Earth, but finding the molecules that form amino acids is an important piece of the puzzle,” said Nozair Khawaja in 2019, with the research team of the Free University of Berlin.
The 2019 findings complement the team’s discovery in 2018 of large, insoluble complex organic molecules believed to float on the surface of Enceladus’ ocean. The team went deeper in 2019 to find the ingredients, dissolved in the ocean, that are needed for the hydrothermal processes that would spur amino acid formation.
Research led by Doug Hemingway with the Carnegie Institute for Science revealed the physics governing the fissures through which oceanwater erupts from the moon’s icy surface, giving its south pole an unusual “tiger stripe” appearance. Images created using Cassini data show that Enceladus’ northern hemisphere was resurfaced with ice relatively recently. This new information adds to the known activity in the southern hemisphere, where Cassini spotted more than 100 geysers blasting icy water into space.
Tidal Effects of the Giant Planet’s Gravity
The eccentricity of the moon’s its orbit generates internal heating. Sometimes it’s a little closer to Saturn and sometimes a littler farther, causing the moon to be slightly deformed, stretched and relaxed, by the tidal effects of the giant planet’s gravity, preventing the moon from freezing completely solid. The moon’s deformation acts to keep the wound from healing—repeatedly widening and narrowing the cracks and flushing water in and out of them—preventing the ice from closing up again.
Now in 2020, NASA researchers spotted the northern changes after looking at the heat signature of Enceladus, using reflected sunlight parsed with Cassini’s visible and infrared mapping spectrometer instrument, or VIMS.
“Thanks to these infrared eyes [on Cassini], you can go back in time and say that one large region in the northern hemisphere appears also young and was probably active not that long ago, in geologic timelines,” Gabriel Tobie, the study co-author and VIMS scientist at the University of Nantes in France, said in a NASA statement about the Cassini infrared images of Enceladus, where the reddish areas indicate fresh ice that has been deposited on the surface. (Image credit: NASA/JPL-Caltech/University of Arizona/LPG/CNRS/University of Nantes/Space Science Institute)
The team combined VIMS data with visible imagery captured by Cassini to create the new, global map of Enceladus in multiple wavelengths of light, both infrared and visible. The map shows that the infrared signals correlate with recent geologic activity on the moon.
“The infrared shows us that the surface of the south pole is young, which is not a surprise because we knew about the jets that blast icy material there,” said Tobie, co-author of the new research published in Icarus that showed heat signatures matching up with the “tiger stripe” fissures near Enceladus’ south pole.
To the surprise of scientists, however, the new map also shows infrared features in the moon’s northern hemisphere, suggesting that icy resurfacing also happened in the north, but how is not yet clear. The changes could have been due to more icy jets, or slower ice movements through cracks in the crust, team members said.
NASA has no future mission planned to probe Enceladus, although scientists made the pitch for one during a presentation coordinated by the U.S. National Academies of Sciences on March 31. The 2020 research was led by Rozenn Robidel, a researcher at the laboratory of planetology and geodynamics at France’s National Centre for Scientific Research (CNRS).
The Daily Galaxy, Sam Cabot, via NASA/Jet Propulsion Laboratory