Saturn’s moon Enceladus has buried ‘churning’ ocean currents under its 12 miles of ice, according to new study
It is already known that Enceladus – one of Saturn’s 82 moons – hides water beneath its shiny, icy surface.
But experts at California Institute of Technology (Caltech) think the ocean currents on Enceladus are a bit like those near Antarctica, powered by salt water.
They based their estimates on computer modeling that used data collected by NASA’s no longer operational Cassini spacecraft.
Enceladus is one of the few solar system locations with liquid water, along with the Earth and Moon of Jupiter Europa, making it an interesting target for astrobiologists.
The new research could inform scientists where they might one day look for signs of life on Enceladus during future satellite missions, Caltech said.
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Enceladus (pictured in image from NASA’s Cassini satellite) is the sixth largest of Saturn’s moons, measuring about 500 miles in diameter. The moon is covered with a shimmering layer of clean ice, making it one of the most reflective bodies in the solar system.
ENCELADUS: FAST FACTS
Discovered: August 28, 1789
Type: Ice moon
Diameter: 313 miles (504 km)
Turnaround time: 32.9 hours
Length of the day: 32.9 hours
Mass: About 680 times less than Earth’s moon
“ Understanding which parts of the subterranean ocean are perhaps the most hospitable to life, as we know it, could one day lead to attempts to look for signs of life, ” said study author Andrew Thompson, professor of environmental science and engineering at Caltech.
Enceladus – Saturn’s sixth largest moon of the 82 in all – is a frozen sphere only 503 miles in diameter (about one-seventh the diameter of Earth’s moon).
Enceladus is covered in a glittering layer of clean ice, making it one of the most reflective bodies in the solar system.
Despite its relatively small size, Enceladus caught the attention of scientists in 2014 thanks to data from Cassini.
At the time, the brave spacecraft discovered evidence of its vast subterranean ocean and sampled water from geyser-like eruptions that occur through fissures in the ice at the South Pole.
Jets of water and some solid particles such as ice crystals spray from fractures in the frozen surface called ‘tiger stripes’.
Despite the fact that Earth and Enceladus harbor water, the ocean on Enceladus is almost completely different from Earth’s.
Earth’s ocean is relatively shallow, at an average of 3.6 kilometers, and covers three-quarters of the Earth’s surface.
Our ocean is also warmer at the top due to the sun’s rays and colder in the depths near the sea floor, and has currents affected by wind.
Enceladus, meanwhile, appears to have a completely subterranean ocean at least 30 km deep, running all the way around the moon.
Illustration of the interior of Saturn’s moon Enceladus with a global ocean of liquid water between the rocky core and the ice crust. The thickness of the layers shown here is not to scale
The ocean of Enceladus is cooled at the top by the ice shell and warmed at the bottom by heat from the core of the moon.
Despite their differences, the oceans of Enceladus and the Earth share one important characteristic: they are salty.
Salinity variations could serve as drivers of ocean circulation on Enceladus, just as they do in Earth’s Southern Ocean, which surrounds Antarctica.
Gravity measurements and heat calculations from Cassini had already shown that Enceladus’s ice cover is thinner at the poles than at the equator.
Unsurprisingly, areas of thin ice at the poles are likely associated with melting, while areas of thick ice at the equator are associated with freezing, Thompson said.
But this affects the ocean currents because when salt water freezes, it releases salts and the surrounding water becomes heavier, causing it to sink.
The opposite happens in areas of thin ice at the poles associated with melting.
Cassini is shown here in a NASA illustration. Cassini was launched in October 1997 from Cape Canaveral, Florida
A computer model, based on Thompson’s studies of Antarctica, suggests that the areas of freezing and melting identified by the ice structure would be connected by the ocean currents.
This would create a pole-to-equator circulation, almost like a conveyor belt, that affects the distribution of heat and nutrients.
The theory challenges current thinking that Enceladus’s global ocean is homogeneous, save for some vertical mixing driven by the heat of its core.
“Knowing the distribution of ice allows us to limit the circulation patterns,” says Ana Lobo, a graduate of Caltech.
An idealized computer model, based on Thompson’s studies of Antarctica, suggests that the areas of freezing and melting identified by the ice structure would be linked by the ocean currents.
‘This creates a polar-to-equator circulation that affects the distribution of heat and nutrients.’
Scientists are still reaping the benefits of the rich data obtained by the Cassini robotic spacecraft, which was active for nearly 20 years after its launch in October 1997.
Cassini’s mission ended in September 2017 when it was deliberately flown to Saturn’s upper atmosphere before it ran out of fuel.
In 2019, Cassini data revealed that a lake on Saturn’s largest moon, Titan, is rich in methane and is 90 meters deep.
Another 20 new moons were confirmed orbiting the planet in 2019, making it the “ moon king ” of the solar system, beating Jupiter’s total of 79.
The new study is published in Nature Geoscience
WHAT DID CASSINI DISCOVER DURING HIS 20 YEAR MISSION TO SATURN?
Cassini launched in 1997 from Cape Canaveral, Florida, then spent seven years in transit, followed by 13 years orbiting Saturn.
An artist’s impression of the Cassini spacecraft studying Saturn
In 2000, it studied Jupiter for six months before reaching Saturn in 2004.
At the time, it discovered six more moons around Saturn, three-dimensional structures towering over Saturn’s rings, and a massive storm that raged across the planet for nearly a year.
On December 13, 2004, it made its maiden flight past Saturn’s moons Titan and Dione.
On December 24, it released the European Space Agency-built Huygens probe on Saturn’s moon Titan to study the atmosphere and surface composition.
There, it discovered eerie hydrocarbon lakes made of ethane and methane.
In 2008, Cassini completed its primary mission to explore the Saturn system and began its mission expansion (the Cassini Equinox mission).
In 2010 it began its second mission (Cassini Solstice Mission) which lasted until it exploded in Saturn’s atmosphere.
In December 2011, Cassini acquired the highest resolution images of Saturn’s moon Enceladus.
In December of the following year, it tracked the transit of Venus to test the feasibility of observing planets beyond our solar system.
In March 2013, Cassini made the last flyby of Saturn’s moon Rhea and measured its internal structure and gravity.
Cassini not only studied Saturn, but also captured incredible images of its many moons. The above image shows Saturn’s moon Enceladus floating in front of the rings and the small moon Pandora. It was captured on November 1, 2009, with the entire scene lit from behind by the sun
In July of that year, Cassini captured a black-lit Saturn to examine the rings in great detail and also captured an image of Earth.
In April of this year, it completed its closest flyaway from Titan and began its Grande Finale orbit ending September 15.
“The mission has changed the way we think about where life has evolved beyond our Earth,” said Andrew Coates, head of the Planetary Science Group at Mullard Space Science Laboratory at University College London.
“Besides Mars, the moons of outer planets such as Enceladus, Europa and even Titan are now the best contenders for life elsewhere,” he added. “We’ve completely rewritten the Saturn textbooks.”