Posted on by Paul Scott Anderson

Enceladus and its Water Geysers Pose Again for Cassini

View of Enceladus' surface, image taken October 19, 2011. NASA/JPL-Caltech/Space Science Institute

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Saturn’s tiny moon Enceladus was the centre of attention for the Cassini spacecraft again last week, with beautiful new photos being released of the moon and its water vapour geysers erupting from the south pole. Some views show surface detail on the moon, some are of the geysers themselves and there is a very nice shot of Enceladus silhouetted against Saturn and its rings in the background. There is even a dual ultraviolet stellar occultation in which two of the stars in the belt of the constellation Orion are seen shining through the plumes! Even though these are still raw, unprocessed images, they again capture the beauty of Enceladus and the Saturnian system.

These new images were taken October 19, 2011 during the E-15 flyby, in which Cassini flew about 1,230 kilometres (765 miles) above the surface of Enceladus. The geysers can be seen in the image below, albeit these are not the closest views that Cassini has obtained. Still, it can be clearly seen how far they extend out from the moon, for a few hundred kilometres.

Enceladus and its water vapour geysers, image taken October 19, 2011. Credit: NASA/JPL-Caltech/Space Science Institute

Some surface detail can be seen in the next image below, a hint of the geological complexity of this moon, most notably seen in the “tiger stripe” fissures at the south pole, where the geysers erupt from inside the moon, escaping to the vacuum of space outside, where the water vapour freezes and falls back to the surface of Enceladus as a form of snow. As some have suggested, Enceladus may be a good place for skiing (with the snow being a very fine powder, although the extremely low gravity would probably interfere too much…)!

Enceladus silhouetted against the clouds and rings of Saturn in the background (the rings are edge-on in this view), image taken October 19, 2011. Credit: NASA/JPL-Caltech/Space Science Institute

Having a personal fascination with Enceladus, I was reminded of an older “Captain’s Log” entry on the CICLOPS web site (2006), by Cassini imaging team leader Carolyn Porco, after the initial discovery of the geysers. In part:

“Our detailed analyses of these images have led us to a remarkable conclusion, documented in a paper to be published in the journal SCIENCE tomorrow, that the jets are erupting from pockets of liquid water, possibly as close to the surface as ten meters… a surprising circumstance for a body so small and cold. Other Cassini instruments have found that the fractures on the surface and the plume itself contain simple organic materials, and that there is more heat on average emerging from the south polar terrain, per square meter, than from the Earth.

Gathering all the evidence and steeling ourselves for the “shockwave spread ’round the world”, we find ourselves staring at the distinct possibility that we may have on Enceladus subterranean environments capable of supporting life. We may have just stumbled upon the Holy Grail of modern day planetary exploration. It doesn’t get any more exciting than this.

A great deal more analysis and further exploration with Cassini must ensue before this implication becomes anything more than a suggestion. But at the moment, the prospects are staggering. Enceladus may have just taken center stage as the body in our solar system, outside the Earth, having the most easily accessible bodies of organic-rich water and, hence, significant biological potential.

Many years from now, it may well be that we and those who follow us will look back on these explorations of Saturn and take our discoveries on this otherwise cold little world to be the most wondrous of any we’ve ever made.

Future explorers of Saturn will have much to look forward to.”

Posted on by Paul Scott Anderson

A Tale of Three Moons: Is There Life in the Outer Solar System?

The cracked ice surface of Europa. Credit: NASA/JPL

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Until fairly recently, the search for life elsewhere in the solar system has focused primarily on Mars, as it is the most Earth-like of all the other planets in the solar system. The possibility of finding any kind of life farther out in the outer solar system was considered very unlikely at best; too cold, too little sunlight, no solid surfaces on the gas giants and no atmospheres to speak of on any of the moons apart from Titan.

But now, some of the places that were previously considered the least likely to hold life have turned out to be perhaps some of the most likely to provide habitable environments. Moons that were thought be cold and frozen for eons are now known to be geologically active, in surprising ways. One of them is the most volcanically active place known in the solar system. At least two others appear to have oceans of liquid water beneath their surfaces. That’s right, oceans. And geysers. On the surface, they are ice worlds, but below, they are water worlds. Then there’s the one with rain, rivers, lakes and seas, but made of liquid methane instead of water. Billions of kilometres farther out from the Sun than the Earth. Who would have thought? Let’s look at those last three in a bit more detail…

Ever since the film 2001: A Space Odyssey first came out, Europa has been the subject of fascination. A small, icy moon orbiting Jupiter, its depiction in that movie, as an inhabited world beneath its ice crust was like a sort of foreshadowing, before the Voyager and Galileo spacecraft gave us our first real close-up looks of this intriguing place. Its surface shell of ice is covered with long cracks and fissures, giving it an appearance much like ice floes at the poles on Earth. More surprising though, was the discovery that, also like on Earth, this ice cover most likely is floating on top of a deep layer of liquid water below. In Europa’s case though, the water layer appears to cover the entire moon, a global subsurface ocean. How is this possible? If there is liquid water, there must be heat (or high concentrations of salts or ammonia), and if you have water and heat, could there be something living in those waters? Gravitational tugging from Jupiter indeed appears to provide enough heat to keep the water liquid instead of frozen. The environment is now thought to be similar to ocean bottoms on Earth. No sunlight, but if there are volcanic vents generating heat and minerals, as on Earth, such a spot could be ideal for at least simple forms of life. On Earth, places like these deep in the oceans are brimming with organisms which don’t require sunlight to survive.

Water vapour geysers on Enceladus. Credit: NASA/JPL

Then there’s Enceladus. Another very small icy moon, orbiting Saturn. Geological activity was considered very unlikely on such a tiny world, only a few hundred kilometres in diameter. But then Cassini saw the geysers, plumes of material erupting from the south polar region through large, warmer cracks nicknamed “tiger stripes.” Cassini has now flown directly through the geysers, analyzing their composition, which is mostly water vapour, ice particles, salts and organics. The latest analysis based on the Cassini data indicates that they almost certainly originate from a sea or ocean of liquid water below the surface. Warm, salty water loaded with organics; could Enceladus be another possible niche for extraterrestrial life? As with Europa, only further missions will be able to answer these questions, but the possibilities are exciting.

Radar image of one of many methane lakes on Titan. Credit: NASA/JPL

Titan is even more fascinating in some ways, the largest moon of Saturn. It is perpetually shrouded in a thick smoggy atmosphere of nitrogen and methane, so the surface has never been visible until now, when Cassini, and its small lander probe Huygens, first looked below the smog and clouds. Titan is like an eerily alien version of Earth, with rain, rivers, lakes and seas, but being far too cold for liquid water (not much heat here), its “water cycle” is composed of liquid methane/ethane. Appearance-wise, the surface and geology look amazingly Earth-like, but the conditions are uniquely Titan. For that reason, it has long been considered that the chances of any kind of life existing here are remote at best. In the last few years however, some scientists are starting to consider the possibility of life forming in just such environments, using liquids other than water, even in such cold conditions. Could life occur in a liquid methane lake or sea? How would it differ from water-based life? Last year, a discovery was made which might be interpreted as evidence of methane-based life on Titan – a seeming disappearance of hydrogen from the atmosphere near the surface and a lack of acetylene on the surface. Previous theoretical studies had suggested that those two things, if ever found, could be evidence for methane-based lifeforms consuming the hydrogen and acetylene. All of this is still highly speculative, and while a chemical explanation is probably more likely according to the scientists involved, a biological one cannot be ruled out yet. Future proposed missions for Titan include a floating probe to land in one of the lakes and a balloon to soar over the landscape, pursuing such mysteries as never before. How cool is that?

Oh, and the moon that is the most volcanically active place in the solar system? Io, although with the only known forms of liquid there being extremely hot lavas on that sulfuric hothouse, the chances of life are still thought to be unbelievably slim. But that’s ok when you start to find out that worlds with oceans and lakes, etc. may be much more common than previously imagined…

Posted on by Nancy Atkinson

Suitable For Framing: Latest Eye Candy from Cassini

Enceladus and Tethys hang below Saturn's rings in this image from the Cassini spacecraft. Credit: NASA/JPL-Caltech/SS

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Another Cassini stunner! This gorgeous, suitable-for-framing image shows two of Saturn’s moons hanging below the planet’s rings, as if strung on a necklace. Beautiful! Enceladus (504 kilometers, 313 miles across) appears just below the rings, while Tethys (1062 kilometers, 660 miles across) appears below. In this shot, Cassini is also closer to Tethys than Enceladus: the spacecraft is 208,000 kilometers (139,000 miles) from Tethys and 272,000 kilometers (169,000 miles) from Enceladus. This image was taken on September 13, 2011.

See below for some raw images from Cassini’s October 1 close fly by of Enceladus, including a great shot of the moon hovering in front of Saturn’s rings, and a view of the geysers.


A closeup view of Enceladus with Saturn's rings in the background. This raw image was taken on Oct. 1, 2011. Credit: NASA/JPL/Space Science Institute

A view of Enceladus from farther away, with the rings slicing through the view of Saturn in the background. Credit: NASA/JPL/Space Science Institute
A view of the geysers on Enceladus, from Cassini's latest close flyby of the moon, on October 1, 2011.Credit: NASA/JPL/Space Science Institute
Posted on by Tammy Plotner

Water, Water Everywhere… And A Few Drops For Saturn, Too!

Recent Cassini images of Saturn's moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. This image was taken looking more or less broadside at the "tiger stripe" fractures observed in earlier Enceladus images. It shows discrete plumes of a variety of apparent sizes above the limb (edge) of the moon. This image was acquired on Nov. 27, 2005. Image Credit: NASA/JPL/Space Science Institute

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In 2005, NASA’s Cassini spacecraft gave us an incredible view of Enceladus chuffing out fountains of water vapor and ice. This action creates an enormous halo of gas, dust and ice that surrounds this Saturnian satellite and enables the planet’s E ring. Now Enceladus is once again in the spotlight as the only moon in the Solar System known to significantly contribute to its parent planet’s chemistry.

Earlier this year, ESA announced that its Herschel Space Observatory had observed a huge torus of water vapor around Saturn which apparently originated from Enceladus. It spans approximately 600,000 kilometers across and runs about 60,000 kilometers deep, but more so than its size is what it appears to be doing… adding water to Saturn’s upper atmosphere. Because the vapor isn’t detectable at visible wavelengths, this observation came as revelation for the Herschel scope.

“Herschel is providing dramatic new information about everything from planets in our own solar system to galaxies billions of light-years away,” said Paul Goldsmith, the NASA Herschel project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California.

While the Herschel infrared observation is new, the indication of a vapor torus around Saturn isn’t. NASA’s Voyager and Hubble missions had given astronomers clues in the past. In 1997, the European Space Agency’s Infrared Space Observatory cited water in Saturn’s atmosphere and two years later NASA’s Submillimeter Wave Astronomy Satellite confirmed it again. But this confirmation only added up to a puzzle. Water found in Saturn’s lower cloud levels couldn’t rise past the colder, upper deck… So where was the water coming from? The answer came in the form of Herschel’s observations and some very astute computer modeling.

“What’s amazing is that the model, which is one iteration in a long line of cloud models, was built without knowledge of the observation.” says Tim Cassidy, a recent post-doctoral researcher at JPL who is now at the University of Colorado’s Laboratory for Atmospheric and Space Physics, Boulder. “Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren’t expecting such detailed ‘images’ of the torus, and the match between model and data was a wonderful surprise.”

Through these simulations, researchers hypothesized that much of the water in the torus was simply lost to space and some is pulled back by gravity to add material to Saturn’s rings. However, it’s the 3-5% that made it back to Saturn’s atmosphere that’s the most interesting. Just how much water vapor is out there? Thanks to combining information from both Herschel and the Ultraviolet Imaging Spectrograph (UVIS) instrument aboard the Cassini spacecraft, we’ve learned that about 12,000 kilograms is being ejected from Enceladus every minute. Can you image how much that would add up to in the period of a year… or more?!

“With the Herschel measurements of the torus from 2009 and 2010 and our cloud model, we were able to calculate a source rate for water vapor coming from Enceladus,” said Cassidy. “It agrees very closely with the UVIS finding, which used a completely different method.”

“We can see the water leaving Enceladus and we can detect the end product — atomic oxygen — in the Saturn system,” said Cassini UVIS science team member Candy Hansen, of the Planetary Science Institute, Tucson, Ariz. “It’s very nice with Herschel to track where it goes in the meantime.”

A tiny percentage adds up to some mighty big numbers, and the water molecules from the torus impact Saturn’s atmosphere to a great degree by contributing hydrogen and oxygen.

“When water hangs out in the torus, it is subject to the processes that dissociate water molecules,” said Hansen, “first to hydrogen and hydroxide, and then the hydroxide dissociates into hydrogen and atomic oxygen.” This oxygen is dispersed through the Saturn system. “Cassini discovered atomic oxygen on its approach to Saturn, before it went into orbit insertion. At the time, no one knew where it was coming from. Now we do.”

Very few days go by that we don’t learn something new about the Solar System and its inner workings. Thanks to observations like those done by the Herschel Space Observatory and missions like Cassini-Huygens, we’re able to further understand the dynamics behind the beauty… and how a tiny player can carry a major role.

“The profound effect this little moon Enceladus has on Saturn and its environment is astonishing,” said Hansen.

Original Story Source: JPL News Release.

Posted on by Ken Kremer

Cassini’s Majestic Saturn Moon Quintet

A quintet of Saturn's moons come together in the Cassini spacecraft's field of view for this portrait. From left to right: Janus, Pandora, Enceladus, Mimas and Rhea. Credit: NASA/JPL-Caltech/Space Science Institute

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Check out this gorgeous new portrait of a Saturnian moon quintet taken by Earths’ emissary – NASA’s Cassini Orbiter. The moons are majestically poised along a backdrop of Saturn’s rings, fit for an artist’s canvas.

Janus, Pandora, Enceladus, Mimas and Rhea are nearly lined up (from left to right) in this view acquired by Cassini at a distance of approximately 684,000 miles (1.1 million kilometers) from Rhea and 1.1 million miles (1.8 million kilometers) from Enceladus.

The newly released image was taken by Cassini’s narrow angle camera on July 29, 2011. Image scale is about 4 miles (7 kilometers) per pixel on Rhea and 7 miles (11 kilometers) per pixel on Enceladus.

Cassini will stage a close flyby of Enceledus – Satarn’s geyser spewing moon – in about two weeks, swooping within 99 km

Moon Facts from JPL:
Janus (179 kilometers, or 111 miles across) is on the far left. Pandora (81 kilometers, or 50 miles across) orbits between the A ring and the thin F ring near the middle of the image. Brightly reflective Enceladus (504 kilometers, or 313 miles across) appears above the center of the image. Saturn’s second largest moon, Rhea (1,528 kilometers, or 949 miles across), is bisected by the right edge of the image. The smaller moon Mimas (396 kilometers, or 246 miles across) can be seen beyond Rhea also on the right side of the image.

This view looks toward the northern, sunlit side of the rings from just above the ring plane. Rhea is closest to Cassini here. The rings are beyond Rhea and Mimas. Enceladus is beyond the rings.

The simple graphic below shows dozens of Saturn’s moons – not to scale. So far 62 have been discovered and 53 have been officially named.

Saturn’s moons. Click on link below to learn more about each moon. Credit: NASA/JPL

Learn more about Saturn’s moons at this link

List of Saturn’s officially named moons:
Aegaeon, Aegir, Albiorix, Anthe, Atlas, Bebhionn, Bergelmir, Bestla, Calypso, Daphnis, Dione, Enceladus, Epimetheus, Erriapus, Farbauti, Fenrir, Fornjot, Greip, Hati, Helene, Hyperion, Hyrrokkin, Iapetus, Ijiraq, Janus, Jarnsaxa, Kari, Kiviuq, Loge, Methone, Mimas, Mundilfari, Narvi, Paaliaq, Pallene, Pan, Pandora, Phoebe, Polydeuces, Prometheus, Rhea, Siarnaq, Skadi, Skoll, Surtur, Suttung, Tarqeq, Tarvos, Telesto, Tethys, Thrym, Titan and Ymir.

Posted on by Nancy Atkinson

Enceladus Rains Water on Saturn

At least four distinct plumes of water ice spew out from the south polar region of Saturn's moon Enceladus. Credit: NASA/JPL/Space Science Institute

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It’s raining on Saturn! Well, kind of. Actually, not really. But there’s some really cool news about Saturn, Enceladus and water – great topics, all. The bubbly water shooting from the moon Enceladus is responsible for the “mystery” water that was found in Saturn’s upper atmosphere several years ago. Observations with the Herschel space observatory has shown that water ice from geysers on Enceladus forms a giant ring of water vapor around Saturn.

Astronomers from the ESA’s Infrared Observatory discovered the presence of trace amounts of water in Saturn’s atmosphere back in 1997, but couldn’t really find an explanation for why it was there and how it got there. Water vapor can’t be seen in visible light, but Herschel’s infrared vision was able to track down the source of the water vapor.

Enceladus expels around 250 kg of water vapor every second, through a collection of jets from the south polar region known as the Tiger Stripes because of their distinctive surface markings. Much of the ice ends up in orbit around Saturn, creating the hazy E ring in which Enceladus resides.

But a small amount reaches Saturn – about 3% to 5% of Enceladus’s ejected water ends up on the home planet of Saturn.

Phil Plait, The Bad Astronomer figured out that a decent rain shower on Earth is 7,000,000,000,000 times heavier than the rainfall on Saturn. So, not a lot of water makes it to Saturn.

But the fact that a moon is having an effect on its planet is unprecedented, as far as we know.

“There is no analogy to this behaviour on Earth,” said Paul Hartogh, Max-Planck-Institut für Sonnensystemforschung, in Germany, who led the collaboration on the analysis of these results. “No significant quantities of water enter our atmosphere from space. This is unique to Saturn.”

The running theory is that Enceladus has a liquid subsurface ocean of Perrier-like bubbly (and maybe salty) water. No one knows yet how much water lies beneath the moon’s surface, but it is thought that the pressure from the rock and ice layers above combined with heat from within force the water up through the Tiger Stripes. When this water reaches the surface it instantly freezes, sending plumes of ice particles hundreds of miles into space.

The total width of the torus is more than 10 times the radius of Saturn, yet it is only about one Saturn radius thick. Enceladus orbits the planet at a distance of about four Saturn radii, replenishing the torus with its jets of water.

The water in Saturn’s upper atmosphere is ultimately transported to lower levels, where it condenses. But scientists say the amounts are so tiny that the resulting clouds are not observable.

Again, despite its enormous size, this torus has it has escaped detection until now because of how water vapor is transparent to visible light but not at the infrared wavelengths Herschel was designed to see.

“Herschel has proved its worth again. These are observations that only Herschel can make,” says Göran Pilbratt, ESA Herschel Project Scientist. “ESA’s Infrared Space Observatory found the water vapour in Saturn’s atmosphere. Then NASA/ESA’s Cassini/Huygens mission found the jets of Enceladus. Now Herschel has shown how to fit all these observations together.”

Read the team’s paper here.

Source: ESA

Posted on by Jason Major

Enceladus’ Salty Surprise

Enceladus' signature ice geysers in action. NASA / JPL / SSI

 

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Researchers on the Cassini mission team have identified large salt grains in the plumes emanating from Saturn’s icy satellite Enceladus, making an even stronger case for the existence of a salty liquid ocean beneath the moon’s frozen surface.

Cassini first discovered the jets of water ice particles in 2005; since then scientists have been trying to learn more about how they behave, what they are made of and – most importantly – where they are coming from. The running theory is that Enceladus has a liquid subsurface ocean of as-of-yet undetermined depth and volume, and pressure from the rock and ice layers above combined with heat from within force the water up through surface cracks near the moon’s south pole. When this water reaches the surface it instantly freezes, sending plumes of ice particles hundreds of miles into space.

Enceladus inside the E ring

Much of the ice ends up in orbit around Saturn, creating the hazy E ring in which Enceladus resides.

Although the discovery of the plumes initially came as a surprise, it’s the growing possibility of liquid water that’s really intriguing – especially that far out in the Solar System and on a little 504-km-wide moon barely the width of Arizona. What’s keeping Enceladus’ water from freezing as hard as rock? It could be tidal forces from Saturn, it could be internal heat from its core, a combination of both – or something else entirely… astronomers are still hard at work on this mystery.

Now, using data obtained from flybys in 2008 and 2009 during which Cassini flew directly through the plumes, researchers have found that the particles in the jets closest to the moon contain large sodium- and potassium-rich salt grains. This is the best evidence yet of the existence of liquid salt water inside Enceladus – a salty underground ocean.

“There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than salt water under Enceladus’s icy surface.”

– Frank Postberg, Cassini team scientist, University of Heidelberg, Germany

Looking down into a jetting "tiger stripe"

If there indeed is a reservoir of liquid water, it must be pretty extensive since the numerous plumes are constantly spraying water vapor at a rate of 200 kg (400 pounds) every second – and at several times the speed of sound! The plumes are ejected from points within long, deep fissures that slash across Enceladus’ south pole, dubbed “tiger stripes”.

Recently the tiger stripe region has also been found to be emanating a surprising amount of heat, even further supporting a liquid water interior – as well as an internal source of energy. And where there’s liquid water, heat energy and organic chemicals – all of which seem to exist on Enceladus – there’s also a case for the existence of life.

“This finding is a crucial new piece of evidence showing that environmental conditions favorable to the emergence of life can be sustained on icy bodies orbiting gas giant planets.”

– Nicolas Altobelli, ESA project scientist for Cassini

Enceladus has intrigued scientists for many years, and every time Cassini takes a closer look some new bit of information is revealed… we can only imagine what other secrets this little world may hold. Thankfully Cassini is going strong and more than happy to keep on investigating!

“Without an orbiter like Cassini to fly close to Saturn and its moons — to taste salt and feel the bombardment of ice grains — scientists would never have known how interesting these outer solar system worlds are.”

– Linda Spilker, Cassini project scientist at JPL

The findings were published in this week’s issue of the journal Nature.

Read more in the NASA press release here.

Image credits: NASA / JPL / Space Science Institute

__________________

Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!

Posted on by Nancy Atkinson

Insanely Awesome Raw Cassini Images of Titan and Enceladus

Raw Cassini image of Titan and Enceladus backdropped by Saturn's rings. Image Credit: NASA/JPL/Space Science Institute

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An incredible set of images are beaming back from the Cassini spacecraft as it orbits Saturn, snapping away at the sights. The moons Titan and Enceladus snuggling up together in front of Saturn’s rings creates an amazing view, especially when they are all lined up together. These were taken on May 21, 2011. I’ve posted some of what I think are the most amazing, below, or you can see the whole set at the Cassini raw images page. When the Cassini imaging team gets a chance to process (and colorize) these, they’ll likely go down as some of the most representative images from the entire mission.


Titan snuggles up to Saturn and its rings. Image credit: NASA/JPL/Space Science Institute

Titan, Enceladus and an onside view of Saturn's rings. Credit: NASA/JPL/Space Science Institute

Hat tip to Stu Atkinson!

Posted on by Nancy Atkinson

Enceladus and Saturn are Linked by Electromagnetic Currents

NASA's Cassini spacecraft has spotted a glowing patch of ultraviolet light near Saturn's north pole that marks the presence of an electrical circuit that connects Saturn with its moon Enceladus. Two images obtained by Cassini's ultraviolet imaging spectrograph on Aug. 26, 2008, separated by 80 minutes, showing how the ‘footprint’ moved according to changes in the position of Enceladus. Credit: NASA/JPL/University of Colorado/Central Arizona College

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The geysers and jets of Enceladus have just become more intriguing. A glowing patch of ultraviolet light near Saturn’s north pole appears to be evidence of a magnetic connection between the planet and the icy, geyser-spewing moon. Data from the Cassini spacecraft have revealed that the jets of gas and icy grains that emanate from the south pole of Enceladus become electrically charged and form an ionosphere, and the motion of Enceladus and its ionosphere through a magnetic bubble that surrounds Saturn acts like a dynamo, setting up a newly-discovered electrical current system that links the moon to the planet.

This video demonstrates the hiss-like radio noise generated by electrons moving along magnetic field lines from Enceladus to a glowing patch of ultraviolet light on Saturn.

Cassini’s Plasma Spectrometer’s electron spectrometer, (CAPS-ELS) has detected the beams of electrons that flow back and forth between Saturn and Enceladus. Magnetic field lines, invisible to the human eye but detectable by the fields and particles instruments on the spacecraft, arc from Saturn’s north polar region to south polar region. Enceladus resides in the arc of a set of the field lines and feeds charged particles into the Saturn atmosphere. The finding is part of a paper published in Nature.

From data Cassini collected in 2008, scientists saw a glowing patch of ultraviolet light emissions near Saturn’s north pole that marked the presence of a circuit between the two bodies, even though the moon is 240,000 kilometers (150,000 miles) away from the planet.

The patch occurs at the end of a magnetic field line connecting Saturn and its moon Enceladus. The area, known as an auroral footprint, is the spot where energetic electrons dive into the planet’s atmosphere, following magnetic field lines that arc between the planet’s north and south polar regions.

“The footprint discovery at Saturn is one of the most important fields and particle revelations from Cassini and ultimately may help us understand Saturn’s strange magnetic field,” said Marcia Burton, a Cassini fields and particles scientist at NASA’s Jet Propulsion Laboratory. “It gives us the first visual connection between Saturn and one of its moons.”

The auroral footprint measures approximately 1,200 kilometers (750 miles) by less than 400 kilometers (250 miles), covering an area comparable to California or Sweden. At its brightest, the footprint shone with an ultraviolet light intensity far less than Saturn’s polar auroral rings, but comparable to the faintest aurora visible at Earth without a telescope in the visible light spectrum. Scientists have not found a matching footprint at the southern end of the magnetic field line.

Scientists already knew that the giant planet Jupiter is linked to three of its moons by charged current systems set up by the satellites orbiting inside its giant magnetic bubble, the magnetosphere, and that these current systems form glowing spots in the planet’s upper atmosphere. The latest discovery at Enceladus shows that similar processes take place at the Saturnian system too.

“This now looks like a universal process — Jupiter’s moon Io is the most volcanic object in the solar system, and produces a bright spot in Jupiter’s aurora, “ said Dr. Andrew Coates from the University College in London, a co-author of the new paper. “Now, we see the same thing at Saturn — the variable and majestic water-rich Enceladus plumes, probably driven by cryovolcanism, cause electron beams which create a significant spot in Saturn’s aurora too.”

Paper: Wayne R. Pryor et al, “The auroral footprint of Enceladus on Saturn”, Nature, 472, 331–333, doi:10.1038/nature09928

Sources: University College, London, NASA

Posted on by Nancy Atkinson

Enceladus’ Internal Heat Much Higher Than Predicted

Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. Credit: NASA/JPL/Space Science Institute

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The south polar region of Enceladus is turning out to be a veritable heat pump. The fissure- and geyser-laden region on this moon of Saturn is churning out internal heat-generated power of about 15.8 gigawatts, which is approximately 2.6 times the power output of all the hot springs in the Yellowstone region, or comparable to 20 coal-fueled power stations. This is more than an order of magnitude higher than scientists had predicted, according to Carly Howett, the lead author of a study published in the Journal of Geophysical Research on March 4. Just how that much power is being generated, however, is unknown.

“The mechanism capable of producing the much higher observed internal power remains a mystery and challenges the currently proposed models of long-term heat production,” said Howett.

2008 data from Cassini’s composite infrared spectrometer indicates a surprisingly high output of temperature from the south polar terrain on Enceladus, which makes it even more likely that liquid water exists below Enceladus’ surface, Howett said.

A 2007 study predicted the internal heat of Enceladus, if principally generated by tidal forces arising from the orbital resonance between Enceladus and another moon, Dione, could be no greater than 1.1 gigawatts averaged over the long term. Heating from natural radioactivity inside Enceladus would add another 0.3 gigawatts.

So these new readings come as a surprise.

This graphic, using data from NASA's Cassini spacecraft, shows how the south polar terrain of Saturn's moon Enceladus emits much more power than scientists had originally predicted. Images credit: NASA/JPL/SWRI/SSI

Recently, scientists studying ice particles ejected from the plumes discovered that some of the particles are salt-rich, and are probably frozen droplets from a saltwater ocean in contact with Enceladus’ mineral-rich rocky core. The presence of a subsurface ocean, or perhaps a south polar sea between the moon’s outer ice shell and its rocky interior would increase the efficiency of the tidal heating by allowing greater tidal distortions of the ice shell.

“The possibility of liquid water, a tidal energy source and the observation of organic (carbon-rich) chemicals in the plume of Enceladus make the satellite a site of strong astrobiological interest,” said Howett, who is a postdoctoral researcher at Southwest Research Institute in Boulder, Colorado.

A possible explanation of the high heat flow observed is that Enceladus’ orbital relationship to Saturn and Dione changes with time, allowing periods of more intensive tidal heating, separated by more quiescent periods. This means Cassini might be “lucky” enough to be seeing Enceladus when it’s unusually active.

The activity is centered on four roughly parallel linear trenches, 130 kilometers (80 miles) long and about 2 kilometers (1 mile) wide, informally known as the “tiger stripes.” These fissures eject great plumes of ice particles and water vapor continually into space, and have elevated temperatures due to heat leaking out of Enceladus’ interior.

Along one fissure, called Baghdad Sulcus, temperatures exceed 180 Kelvin ( – 92 C, -135 F), and may be higher than 200 Kelvin (- 73 C, -100 F). While chilly by Earth standards, peak temperatures, the temperatures are a cozy oasis compared to the numbing 50 Kelvin (-223 C, -370 F) of their surroundings.

Source: JPL