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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What is going on inside Saturn’s moon Enceladus and what powers the icy geysers and jets? A pair of upcoming flybys by the Cassini spacecraft could help answer those questions. Radio instruments on board will measure the gravity field of Enceladus and focus particularly on the very intriguing south polar hot spot.
Of course, the success of these flybys hinges on the Cassini mission controllers being able to wake up the dormant spacecraft which has been in safe mode since November 2. Teams will attempt to get Cassini up and running again tomorrow, November 24, and they don’t anticipate any problems.
Cassini went into the protective standby mode and the likely cause of the problem was a faulty program code line, or a flipped bit in the spacecraft’s command and data system computer.
The upcoming flybys of Enceladus will put Cassini very close – about 48 kilometers (30 miles) above the surface. The first will take place on November 30. Pairing this flyby with one on April 28, should provide scientists enough information to determine the nature of the interior right under the hot spot. The next flyby on December 21, Cassini will make 50-kilometer pass over the north pole of Enceladus. The fields and particles instruments will be trying to “sniff” anything coming from the moon.
There will be two three-hour “wing” observations before and after closest-approach (from five to eight hours from closest approach on either side), and then three more hours centered directly around closest approach. The Cassini team is throwing almost the entire gamut of instruments into the flyby program, between radio science (RSS) observations, the imaging science system (ISS) and composite infrared spectrometer (CIRS) which will observe this moon on the inbound leg, and CIRS and the visible and infrared mapping spectrometer (VIMS) which will take data on the outbound leg, with other optical remote sensing and fields, particles and waves instruments also taking data.
An artist illustration of the Cassini spacecraft. Credit: NASA/JPL
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NASA announced that the Cassini spacecraft in orbit around Saturn will have its suite of scientific cameras offline until at least Nov. 24. Cassini is currently in safe mode due to a malfunction in the spacecraft’s computer. This shut down all non-essential systems to prevent any further damage happening to the spacecraft. This means that all scientific efforts on the mission have been suspended until the problem can be resolved.
Although these seem like severe issues, mission managers are relatively sure that they will have no serious long-term effects on the overall mission. Cassini entered safe mode around 4 p.m. PDT (7 p.m. EDT) on Tuesday, Nov. 2. Managers want to review what took place onboard Cassini, correct what they can and ensure that this doesn’t happen again. Programmers have already ascertained that the likely cause of the problem was a faulty program code line that made its way back to Cassini.
Cassini captured this startling image of Saturn's moon Hyperion. Photo Credit: NASA/JPL
Ordinarily when faulty code is sent from Earth to Saturn, Cassini would reject any coding that is deemed ‘bad.’ However, this did not happen in this case, causing the problem. Controllers are not totally convinced that a solar fare didn’t corrupt the code on its way out to the gas giant.
“The spacecraft responded exactly as it should have, and I fully expect that we will get Cassini back up and running with no problems,” said Bob Mitchell, Cassini’s program manager at JPL. “Over the more than six years we have been at Saturn, this is only the second safing event. So considering the complexity of demands we have made on Cassini, the spacecraft has performed exceptionally well for us.”
Cassini launched from Cape Canaveral Air Force Station back in 1997 atop a Titan rocket. In the thirteen years since that time it has entered ‘safe’ mode a total of six times.
Cassini discovered that Saturn's moon Enceladus is 'jet-powered' in the form of geysers erupting from the moon's surface into space. Photo Credit: NASA/JPL
The largest loss for Cassini’s planners is this will cost them a flyby of Titan, one of Saturn’s moons and the only moon in the solar system with an appreciable atmosphere. All is not lost however, as there are still some 53 possible flybys of the moon currently scheduled. The mission is currently planned to last until 2017.
The Cassini-Huygens mission is a cooperative program managed between NASA, the European Space Agency (ESA) and the Italian Space Agency. JPL, a division of the California Institute of Technology (Caltech) manages the Cassini program for NASA’s Science Mission Directorate located in Washington, D.C.
Proposed 'Perrier' Ocean for Enceladus. Credit: NASA/JPL/Space Science Institute
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Bottled water companies take note: an exotic form of warm, bubbly mineral water could be what feeds the mysterious jets spraying from the south polar region of Saturn’s moon Enceladus. A new model of the sub-surface ocean explains how the small moon could be so cryo-volcanically active. The Cassini spacecraft has detected sodium and potassium salts, as well as carbonates in the water vapor plumes spewing from the moon, which indicates a liquid, bubbly subsurface ocean. “There is a plume chamber, where some of the bubbles can pop the cap of the thin ice crust, and through that process is how the plumes get sprayed out,” said Dennis Matson, a NASA planetary scientist from JPL, speaking at a press briefing at the American Astronomical Society’s Division for Planetary Sciences meeting in Pasadena, California.
The schematic image (top) is laid on top of a picture of the Enceladus jets taken by Cassini’s imaging cameras in November 2009. It shows bubbles in subsurface seawater traveling through a passage in the ice crust to feed a geyser. The water flows back down to the subsurface ocean through cracks in the ice.
Matson explained the process:
“What we think is going on is that Enceladus has a subsurface ocean where water, heat and chemicals are stored before they erupt,” he said. There is an ice crust, many tens of kilometers thick. The ocean is gas rich, — and previous researchers dubbed such an ocean as a ‘Perrier’ ocean -– which basically “pops the cap” of the ice crust.
“What is happening is that water comes up and pressure is released,” said Matson. “Gases and water come out and the bubbles come near the surface and supply materials to the plumes. Water also transfers laterally, to a great extent, from the point of the plumes. This transfers heat to the surface, by analogy, like the radiator on your car. You have water coming out, which transfers heat to the thin ice layer, and then the heat is radiated to space. Cooled water goes down through cracks in the ice where it gets ready for another trip to the surface. “
This image compares heat flow at Earth and Saturn’s moon Enceladus. Credit: NASA/JPL
Cassini also found an impressive amount of heat flow over a small area coming from Enceladus’ interior. About four years ago, Cassini’s composite infrared spectrometer instrument detected a heat flow in the south polar region of at least 6 gigawatts, the equivalent of at least a dozen electric power plants. This is at least three times as much heat as an average region of Earth of similar area would produce, despite Enceladus’ small size.
“To put the heat flow in perspective,” said Matson, “the heat flow for the Earth has 87 of these units, but on the south pole of Enceladus, 250 units. At Yellowstone, there are 2500 units, but at one of the tiger stripe hots spots on Enceladus, we find heat flow as big as 13,000 units.”
The heat is, of course, relative to the surrounding environment. The subsurface bubbly water is probably just below freezing, which is 273 degrees Kelvin or 32 degrees Farenheit, whereas the surface is a frigid 80 degrees Kelvin or -316 degrees Farenheit. However, Matson said they have also seen surface temperatures as high as 180 K, when only 70 K was expected at the south pole.
Cassini imaging scientists used views like this one to help them identify the source locations for individual jets spurting ice particles, water vapor and trace organic compounds from the surface of Saturn's moon Enceladus. Credit: NASA
Finding the sodium in the icy grains in the plume is huge piece of evidence pointing to a subsurface ocean. Previously, Earth-based observations did not detect salts in the plume, and so scientists didn’t think a liquid ocean was possible. But infrared observations with an instrument on Cassini found the particles in the plumes include water ice, and substantial amounts of sodium and potassium salts and carbonates, as well as organics.
“The sodium was hiding in the little grains,” Matson said. “In the case of Enceladus, sodium isn’t in the vapor, it’s in the solid particles. This was something entirely new that had not been seen elsewhere.”
Also new is that the heat from Enceladus appears to be originating in the ocean, and also the realization there is a circulation system inside the moon, where there is process of pumping the water to the surface.
“This process we’ve outlined, where getting the water up to the surface, you have the heat, the water, and sodium and potassium all from one source that brings that up to the surface. So you have one process that delivers all those things, whereas before we had separate processes to try and explain each of them.”
Titan, Saturn's rings and Enceladus. Credit: NASA/JPL/SSI
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Wow. Cassini the artist has struck again, this time with amazing images from the close flyby of Enceladus that we wrote a preview about earlier this week. Cassini flew by Enceladus during the early hours of May 18 UTC, coming within about 435 kilometers (270 miles) of the moon’s surface. The raw images came in late last night, and in my inbox this morning was an email from Stuart Atkinson, (no relation, but great name) alerting me to the treasures. Stu himself has called this image “the new iconic image of the space age,” and Emily Lakdawalla of the Planetary Blog has called these images “some of the most amazing Cassini has captured yet.”
What you’re seeing here is hazy Titan, backlit by the Sun, with Saturn’s rings in the foreground– plus, at the way bottom is the limb of the night side of Enceladus’ south pole. Emily has created a flipped, annotated image (plus there’s more Enceladus jaw-droppers below:
nceladus, Titan, and the rings of Saturn (explained) Credit: NASA/JPL/SSI/annotated by Emily Lakdawa. Click for larger version.
The 'fountains' of Enceladus. Credit: NASA/JPL/SSI
Three huge “fountains” of Enceladus geysers are visible in this raw image taken by Cassini on May 18, 2010. The camera was pointing toward Enceladus at approximately 14,972 kilometers away, and the image was taken using the CL1 and CL2 filters. Emily, with her photo editing prowess, has created a movie from four different images as Cassini cruised closer to the moon.
Plus there’s this very interesting raw image from Cassini:
Raw image from Cassini on May 18. Credit: NASA/JPL/SSI
Explanations anyone?
Cassini will be flying by Titan in the early hours of May 20 UTC, coming within 1,400 kilometers (750 miles) of the surface. Although Cassini will primarily be doing radio science during this pass to detect subtle variations in the gravitational tug on the spacecraft by Titan, hopefully we’ll see some new visible light images of Titan, as well.
On the left, Saturn's moon Enceladus is backlit by the sun, showing the fountain-like sources of the fine spray of material that towers over the south polar region. On the right, is a composite image of Titan. Image credit: NASA/JPL/SSI and NASA/JPL/University of Arizona
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It’s a space navigator’s dream! The Cassini spacecraft will perform close flybys of two of Saturn’s most enigmatic moons all within less than 48 hours, and with no maneuvers in between. Enceladus and Titan are aligned just right so that Cassini can catch glimpses of these two contrasting moons – one a geyser world and the other an analog to early Earth.
Cassini will make its closest approach to Enceladus late at night on May 17 Pacific time, which is in the early hours of May 18 UTC. The spacecraft will pass within about 435 kilometers (270 miles) of the moon’s surface.
The main scientific goal at Enceladus will be to watch the sun play peekaboo behind the water-rich plume emanating from the moon’s south polar region. Scientists using the ultraviolet imaging spectrograph will be able to use the flickering light to measure whether there is molecular nitrogen in the plume. Ammonia has already been detected in the plume and scientists know heat can decompose ammonia into nitrogen molecules. Determining the amount of molecular nitrogen in the plume will give scientists clues about thermal processing in the moon’s interior.
Then on to Titan: the closest approach will take place in the late evening May 19 Pacific time, which is in the early hours of May 20 UTC. The spacecraft will fly to within 1,400 kilometers (750 miles) of the surface.
Cassini will primarily be doing radio science during this pass to detect the subtle variations in the gravitational tug on the spacecraft by Titan, which is 25 percent larger in volume than the planet Mercury. Analyzing the data will help scientists learn whether Titan has a liquid ocean under its surface and get a better picture of its internal structure. The composite infrared spectrometer will also get its southernmost pass for thermal data to fill out its temperature map of the smoggy moon.
Cassini has made four previous double flybys and one more is planned in the years ahead.
For more information on the Enceladus flyby, dubbed “E10,” see this link.
For more information on the Titan flyby, dubbed “T68,” see this link.
Artist's impression of the Cassini spacecraft making a close pass by Saturn's inner moon Enceladus to study plumes from geysers that erupt from giant fissures in the moon's southern polar region. Copyright 2008 Karl Kofoed/NASA. Click for full size version.
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Observations from two instruments on the Cassini spacecraft shows the moon Enceladus leaves a complex pattern of ripples and bubbles in its wake as it orbit Saturn. The ringed planet’s magnetosphere is filled with electrically charged particles (plasma) originating from both the planet and its moons, and as Enceladus plows through the plasma “spiky” features form that represent bubbles of low energy particles, said Sheila Kanani who led a team of scientists from University College, London who discovered the phenomenon.
Cassini has made nine flybys of the icy, geyser-filled moon Enceladus (Saturn’s sixth-largest moon) since 2005. The closest of these have taken the spacecraft’s suite of instruments just 25 km from Enceladus’s surface, which scientists believe conceals a saline ocean. Heated vents at the south pole of the moon release a plume of material, consisting mainly of icy grains and water vapour, into space.
Measurements from the Cassini Plasma Spectrometer (CAPS) and the Magnetospheric IMaging Instrument (MIMI) show that both the moon and its plume are continuously soaking up the plasma, which rushes past at around 30 kilometers per second, leaving a cavity downstream. In addition, the most energetic particles which zoom up and down Saturn’s magnetic field lines are swept up, leaving a much larger void in the high energy plasma. Material from Enceladus, both dust and gas, is also being charged and forming new plasma.
The mysterious spiky features in the CAPS data shows a complex picture of readjustment downstream from Enceladus.
“Eventually the plasma closes the gap downstream from Enceladus but our observations show that this isn’t happening in a smooth, orderly fashion. We are seeing spiky features in the plasma that last between a few tens of seconds and a minute or two. We think that these might represent bubbles of low energy particles formed as the plasma fills the gap from different directions,” said Kanani. Since Cassini arrived at Saturn, it has been building up a picture of the vital and unexpected role that Enceladus plays in Saturn’s magnetosphere.
“Enceladus is the source of most of the plasma in Saturn’s magnetosphere, with ionised water and oxygen originating from the vents forming a big torus of plasma that surrounds Saturn. We may see these spiky features in the wake of Saturn’s other moons as they interact with the plasma but, to date, we have only studied Enceladus in sufficient detail,” said Kanani.
She presented her results at the Royal Astronomical Society’s National Astronomy Meeting in Glasgow, Scotland this week.
The small moon Janus is almost hidden between the planet's rings and the larger moon Rhea.Credit: NASA/JPL/Space Science Institute
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The Cassini mission keeps churning out the hits, and here’s a collection of some of the latest stunning images released by the CICLOPS (Cassini Imaging for Central Operations) team. Above, the small moon Janus is almost hidden between the planet’s rings and the larger moon Rhea. The northern part of Janus can be seen peeking above the rings in this image of a “mutual event” where Janus (179 kilometers, 111 miles across) moved past Rhea (1,528 kilometers, 949 miles across). Mutual event observations such as this one, in which one moon passes close to or in front of another, help scientists refine their understanding of the orbits of Saturn’s moons. Click here to see a movie of the event.
Saturn's potato-shaped moon Prometheus is rendered in three dimensions in this close-up from Cassini. Credit: NASA/JPL/Space Science Institute
Grab your 3-D glasses for this one! This 3-D view is a close-up of Saturn’s potato-shaped moon Prometheus, showing the moon’s leading hemisphere. The image was created by combining two different black and white images that were taken from slightly different viewing angles. The images are combined so that the viewer’s left and right eye, respectively and separately, see a left and right image of the black and white stereo pair when viewed through red-blue glasses.
Saturn and Enceladus. Credit: NASA/JPL/Space Science Institute
At first glance, you might think this scene simply shows a bright chunk of Saturn, along with a crescent of the moon Enceladus at top right. But a closer look at the center of the image reveals a dramatic surprise: plumes of water ice spew out from the famed fractures known as “tiger stripes” near the south pole of the moon. And one other surprise: Although it may appear that Enceladus (504 kilometers, 313 miles across) is in the background here, the moon actually is closer to the spacecraft than Saturn is. This view looks most directly toward the side of Enceladus that faces away from Saturn. North on Enceladus is up and rotated 1 degree to the left.
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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Newly released images from last November’s close flyby over Saturn’s icy moon Enceladus the Cassini spacecraft reveal geyser jets spraying all along the prominent fractures, or “tiger stripes” that cross the moon’s south polar region. Additionally, a new detailed temperature map of one fracture reveals warmer temperatures than what was expected. “Enceladus continues to astound,” said Bob Pappalardo, Cassini project scientist at the Jet Propulsion Laboratory. “With each Cassini flyby, we learn more about its extreme activity and what makes this strange moon tick.”
The new images from the imaging science subsystem and the composite infrared spectrometer teams include the best 3-D image ever obtained of a tiger stripe fissure that sprays icy particles, water vapor and organic compounds. There are also views of regions not well-mapped previously on Enceladus, including a southern area with crudely circular tectonic patterns. In this unique mosaic image combining high-resolution data from the imaging science subsystem and composite infrared spectrometer aboard NASA's Cassini spacecraft, pockets of heat appear along one of the mysterious fractures in the south polar region of Saturn's moon Enceladus. Image credit: NASA/JPL/GSFC/SWRI/SSI
For Cassini’s visible-light cameras, the Nov. 21, 2009 flyby provided the last look at Enceladus’ south polar surface before that region of the moon goes into 15 years of darkness, and includes the most detailed look yet at the jets.
Scientists planned to use this flyby to look for new or smaller jets not visible in previous images. In one mosaic, scientists count more than 30 individual geysers, including more than 20 that had not been seen before. At least one jet spouting prominently in previous images now appears less powerful.
“This last flyby confirms what we suspected,” said Carolyn Porco, imaging team lead based at the Space Science Institute in Boulder, Colo. “The vigor of individual jets can vary with time, and many jets, large and small, erupt all along the tiger stripes.”
A new map that combines heat data with visible-light images shows a 40-kilometer (25-mile) segment of the longest tiger stripe, known as Baghdad Sulcus. The map illustrates the correlation, at the highest resolution yet seen, between the geologically youthful surface fractures and the anomalously warm temperatures that have been recorded in the south polar region. The broad swaths of heat previously detected by the infrared spectrometer appear to be confined to a narrow, intense region no more than a kilometer (half a mile) wide along the fracture.
In these measurements, peak temperatures along Baghdad Sulcus exceed 180 Kelvin ( – 92 C, -135 F), and may be higher than 200 Kelvin (- 73 C, -100 F). These warm temperatures probably result from heating of the fracture flanks by the warm, upwelling water vapor that propels the ice-particle jets seen by Cassini’s cameras. Cassini scientists will be testing this idea by investigating how well the hot spots correspond with the jet sources.
“The fractures are chilly by Earth standards, but they’re a cozy oasis compared to the numbing 50 Kelvin (-223 C, -370 F) of their surroundings,” said John Spencer, a composite infrared spectrometer team member based at Southwest Research Institute in Boulder, Colo. “The huge amount of heat pouring out of the tiger stripe fractures may be enough to melt the ice underground. Results like this make Enceladus one of the most exciting places we’ve found in the solar system.”
Some of Cassini’s scientists infer that the warmer the temperatures are at the surface, the greater the likelihood that jets erupt from liquid. “And if true, this makes Enceladus’ organic-rich, liquid sub-surface environment the most accessible extraterrestrial watery zone known in the solar system,” Porco said.
The Nov. 21 flyby was the eighth targeted encounter with Enceladus. It took the spacecraft to within about 1,600 kilometers (1,000 miles) of the moon’s surface, at around 82 degrees south latitude.
Caption: Geysers on Enceladus. Credit: NASA, JPL, Space Science Institute
One of the most exciting but unexpected discoveries of the Cassini mission is seeing the activity taking place on Saturn’s small moon Enceladus. Between the active geysers, the unusual “tiger stripes” and the surprisingly young surface near the moon’s south pole, Enceladus has surprised scientists with almost all the images and data the gathered by the spacecraft. But is the moon always active, or are we just in the right place at the right time, lucky to be catching it during an active phase? A recent paper outlines a model in which the kind of geologic eruptions now visible on Enceladus only occur every billion years or so.
“Cassini appears to have caught Enceladus in the middle of a burp,” said Francis Nimmo, a planetary scientist at the University of California Santa Cruz. “These tumultuous periods are rare and Cassini happens to have been watching the moon during one of these special epochs.”
Nimmo and co-author Craig O’Neill of Macquarie University in Sydney, Australia propose that blobs of warm ice that periodically rise to the surface and churn the icy crust on Saturn’s moon Enceladus explain the quirky heat behavior and intriguing surface of the moon’s south polar region.
The most interesting features by far in the south polar region of Enceladus are the fissures known as “tiger stripes” that spray water vapor and other particles out from the moon. While Nimmo and O’Neill’s model doesn’t link the churning and resurfacing directly to the formation of fissures and jets, it does fill in some of the blanks in the region’s history. Enceladus. Credit: NASA/JPL/Space Science Institute
“This episodic model helps to solve one of the most perplexing mysteries of Enceladus,” said Bob Pappalardo, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., of the research done by his colleagues. “Why is the south polar surface so young? How could this amount of heat be pumped out at the moon’s south pole? This idea assembles the pieces of the puzzle.”
But not everyone is convinced this model answers all the questions about Enceladus. Carolyn Porco, who leads the imaging team for Cassini said via Twitter regarding this paper, “Beware! Several different models out there say different things.”
About four years ago, Cassini’s composite infrared spectrometer instrument detected a heat flow in the south polar region of at least 6 gigawatts, the equivalent of at least a dozen electric power plants. This is at least three times as much heat as an average region of Earth of similar area would produce, despite Enceladus’ small size. The region was also later found by Cassini’s ion and neutral mass spectrometer instrument to be swiftly expelling argon, which comes from rocks decaying radioactively and has a well-known rate of decay.
Calculations told scientists it would be impossible for Enceladus to have continually produced heat and gas at this rate. Tidal movement – the pull and push from Saturn as Enceladus moves around the planet – cannot explain the release of so much energy.
The surface ages of different regions of Enceladus also show great diversity. Heavily cratered plains in the northern part of the moon appear to be as old as 4.2 billion years, while a region near the equator known as Sarandib Planitia is between 170 million and 3.7 billion years old. The south polar area, however, appears to be less than 100 million years old, possibly as young as 500,000 years.
O’Neill had originally developed the model for the convection of Earth’s crust. For the model of Enceladus, which has a surface completely covered in cold ice that is fractured by the tug of Saturn’s gravitational pull, the scientists stiffened up the crust. They picked a strength somewhere between that of the malleable tectonic plates on Earth and the rigid plates of Venus, which are so strong, it appears they never get sucked down into the interior. These drawings depict explanations for the source of intense heat that has been measured coming from Enceladus' south polar region. Credit: NASA/JPL
Their model showed that heat building up from the interior of Enceladus could be released in episodic bubbles of warm, light ice rising to the surface, akin to the rising blobs of heated wax in a lava lamp. The rise of the warm bubbles would send cold, heavier ice down into the interior. (Warm is, of course, relative. Nimmo said the bubbles are probably just below freezing, which is 273 degrees Kelvin or 32 degrees Fahrenheit, whereas the surface is a frigid 80 degrees Kelvin or -316 degrees Fahrenheit.)
The model fits the activity on Enceladus when the churning and resurfacing periods are assumed to last about 10 million years, and the quiet periods, when the surface ice is undisturbed, last about 100 million to two billion years. Their model suggests the active periods have occurred only 1 to 10 percent of the time that Enceladus has existed and have recycled 10 to 40 percent of the surface. The active area around Enceladus’s south pole is about 10 percent of its surface.
A liquid plume is spewing from Saturn’s icy moon Enceladus — but is it coming from heated ice on the surface, or a liquid ocean underneath?
Analysis of the plume’s chemistry, detailed in the Cassini (CICLOPS) image above and reported in Nature this week, may put the debate to rest.
Enceladus. Credit: CICLOPS
Lead author Jack Hunter (J.H.) Waite, of the Southwest Research Institute in San Antonio, Texas and his colleagues say ammonia detected in the jets from Enceladus’ south pole provides the strongest evidence yet for the existence of liquid water beneath the surface.
A previous paper led by Frank Postberg of the University of Heidelberg in Germany, published in Nature just last month, reported the discovery of salts in E-ring particles derived from the plume, also suggestive of a liquid reservoir.
But Susan Kieffer of the University of Illinois at Urbana–Champaign and her colleagues proposed in a 2006 Science paper that warm ice is heated near the surface, causing dissociation of clathrate hydrates. And Nicholas Schneider, of the University of Colorado at Boulder, and his colleagues published a paper in the same Nature issue as Postberg’s team (June 24) — reporting that there’s not enough sodium in the plume to support a liquid ocean.
The ammonia may tip the scales, say the authors of the new paper.
“The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180K have been measured near the fractures from which the jets emanate,” the authors write. “We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice.”
Besides ammonia, the authors detected various organic compounds and deuterium — ‘heavy’ hydrogen abundant in the oceans of Earth. Ammonia, together with methanol and salts, acts as an antifreeze, allowing liquid water to exist at below-freezing temperatures. The authors suggest that preserving even a residual oceanic layer during cooling episodes would maintain conditions necessary for tidal heating and geologic activity.
Enceladus is one of only three moons in the Solar System known to be volcanically active. The plume of gas and particles is thought to make up Saturn’s outermost ‘E’ ring.
UT ran a story last month, when Nature ran two papers with different ideas about whether Enceladus harbors a liquid ocean. See that story here.
Source for text: Nature. Source for images: Cassini Imaging Central Laboratory for Operations (CICLOPS), with thanks to study co-author William Lewis for the tip.
