Saturn’s moon Enceladus has ‘churning’ ocean currents buried beneath its 12 miles of ice, according to a new study.
It’s 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 ocean currents are flowing on Enceladus a bit like those near Antarctica, driven by salty water.
They’ve based their estimations on computer modelling that used data gathered by NASA’s no-longer-operational Cassini spacecraft.
Enceladus is one of few locations in the Solar System with liquid water, along with Earth and Jupiter’s moon Europa, making it a target of interest for astrobiologists.
The new research could inform scientists where to one day search for signs of life on Enceladus during future satellite missions, according to Caltech.
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Enceladus (pictured in image from NASA’s Cassini satellite) is the sixth-largest of Saturn’s moons, with a diameter of around 310 miles. The moon is covered in a shimmering layer of clean ice, making it one of the most reflective bodies in the Solar System.
ENCELADUS: QUICK FACTS
Discovered: August 28 1789
Type: Ice moon
Diameter: 313 miles (504km)
Orbital period: 32.9 hours
Length of day: 32.9 hours
Mass: About 680 times less than Earth’s moon
‘Understanding which regions of the subsurface ocean might be the most hospitable to life as we know it could one day inform efforts to search for signs of life,’ said study author Andrew Thompson, professor of environmental science and engineering at Caltech.
Enceladus – Saturn’s sixth-largest moon out of its 82 in total – is a frozen sphere just 313 miles in diameter (about one-seventh the diameter of Earth’s moon).
Enceladus is covered in a shimmering layer of clean ice, making it one of the most reflective bodies in the Solar System.
Despite its relatively small size, Enceladus attracted the attention of scientists in 2014 thanks to data from Cassini.
At the time, the plucky spacecraft discovered evidence of its large subsurface ocean and sampled water from geyser-like eruptions that occur through fissures in the ice at its south pole.
Jets of water and some solid particles such as ice crystal spout from fractures in the frozen surface called ‘tiger stripes’.
Despite the fact Earth and Enceladus harbour water, the ocean on Enceladus is almost entirely unlike Earth’s.
Earth’s ocean is relatively shallow, with an average of 2.2 miles (3.6 km), and covers three-quarters of the planet’s surface.
Our ocean is also warmer at the top thanks to the Sun’s rays and colder in the depths near the seafloor, and has currents that are affected by wind.
Enceladus, meanwhile, appears to have a completely subsurface ocean at least 18.6 miles (30 km) deep, which goes all the way round the moon.
Illustration of the interior of Saturn’s moon Enceladus showing a global liquid water ocean between its rocky core and icy crust. Thickness of layers shown here is not to scale
Enceladus’ ocean is cooled at the top near the ice shell and warmed at the bottom by heat from the moon’s core.
Despite their differences, the oceans of Enceladus and Earth share one important characteristic – they are salty.
Variations in salinity could serve as drivers of the ocean circulation on Enceladus, much as they do in Earth’s Southern Ocean, which surrounds Antarctica.
Gravitational measurements and heat calculations from Cassini had already revealed that Enceladus’ ice shell is thinner at the poles than at the equator.
Unsurprisingly, regions of thin ice at the poles are likely associated with melting, while regions of thick ice at the equator are associated with freezing, Thompson said.
But this affects the ocean currents, because when salty water freezes, it releases the salts and makes the surrounding water heavier, causing it to sink.
The complete opposite happens in regions of thin ice at the poles associated with melting.
Cassini is depicted here in a NASA illustration. Cassini launched from Cape Canaveral, Florida in October 1997
A computer model, based on Thompson’s studies of Antarctica, suggests that the regions 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 influences the distribution of heat and nutrients.
The theory challenges current thinking that Enceladus’ global ocean is homogeneous apart from some vertical mixing driven by the warmth of its core.
‘Knowing the distribution of ice allows us to place constraints on circulation patterns,’ said Caltech graduate student Ana Lobo.
‘An idealised computer model, based on Thompson’s studies of Antarctica, suggests that the regions of freezing and melting, identified by the ice structure, would be connected by the ocean currents.
‘This would create a pole-to-equator circulation that influences the distribution of heat and nutrients.’
Scientists are still reaping the rewards of the rich data obtained by the Cassini robotic spacecraft, which was active for nearly 20 years after launching in October 1997.
Cassini’s mission ended in September 2017 when it was deliberately flown into 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 with methane and 300 feet deep.
Another 20 new moons were confirmed orbiting the planet in 2019, making it ‘moon king’ of the solar system, beating Jupiter’s total of 79.
The new study has been published in Nature Geoscience.
WHAT DID CASSINI DISCOVER DURING ITS 20-YEAR MISSION TO SATURN?
Cassini launched from Cape Canaveral, Florida in 1997, 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 spent six months studying Jupiter before reaching Saturn in 2004.
In that time, it discovered six more moons around Saturn, three-dimensional structures towering above Saturn’s rings, and a giant storm that raged across the planet for nearly a year.
On 13 December 2004 it made its first flyby of Saturn’s moons Titan and Dione.
On 24 December it released the European Space Agency-built Huygens probe on Saturn’s moon Titan to study its atmosphere and surface composition.
There it discovered eerie hydrocarbon lakes made from ethane and methane.
In 2008, Cassini completed its primary mission to explore the Saturn system and began its mission extension (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 obtained 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 outside our solar system.
In March 2013 Cassini made the last flyby of Saturn’s moon Rhea and measured its internal structure and gravitational pull.
Cassini didn’t just study Saturn – it also captured incredible views of its many moons. In the image above, Saturn’s moon Enceladus can be seen drifting before the rings and the tiny moon Pandora. It was captured on Nov. 1, 2009, with the entire scene is backlit by the Sun
In July of that year Cassini captured a black-lit Saturn to examine the rings in fine detail and also captured an image of Earth.
In April of this year it completed its closest flyby of Titan and started its Grande Finale orbit which finished on September 15.
‘The mission has changed the way we think of where life may have developed beyond our Earth,’ said Andrew Coates, head of the Planetary Science Group at Mullard Space Science Laboratory at University College London.
‘As well as Mars, outer planet moons like Enceladus, Europa and even Titan are now top contenders for life elsewhere,’ he added. ‘We’ve completely rewritten the textbooks about Saturn.’