25. ----------------------------
Fast and Slow Water Ion Populations in the Enceladus Plume
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JA027591
RP Haythornthwaite et al, 2020
Extracts - Enceladus plumes were found to originate from diffuse sources and collimated geyser-like jets. The jets were associated with a series of 4 fissures, commonly known as the “Tiger Stripes,” that dominate the south polar terrain. From libration measurements and the jets, the existence of a 20–50 km deep global subsurface ocean was inferred, its presence also being necessary to supply the jets with material. The ocean itself is buried under a 20–30 km thick ice layer. Around the south pole, the ocean increases by 10 km in depth, while the ice thickness has a corresponding decrease, thinning out to between 2 and 5 km thick.
Water is the major constituent in all three plume phases : dust, gas, and ions. The gas consists of neutral molecules with Water ice comprising up to 98%, with other major species being Carbon dioxide, Methane, Ammonia, and Hydrogen. There are also hydrocarbons, alcohols, and nitriles detected at below 0.2% relative abundance to water.
The plume gas emission has been shown to contain 2 distinct water components - a thermal population and a supersonic population. The thermal component arises from sublimation or through molecules interacting with fissure walls. The bulk velocities of these neutral water molecules in the plume have been estimated between 500 and 750 m/s. The supersonic water population has been associated with driven fast gas emission from fissures. Some studies have found velocities from 1.2 km/s up to 2.6 km/s.
One of them suggested Mach 10 velocities, corresponding to jet velocities of 6 km/s, using a thermal velocity of 576 m/s. Another paper found velocities in excess of Mach 5 (1.5 km/s), caused by narrow jets at the vent. They found that Vents 3, 4, and 6 were the strongest influences during the E5 flyby. A different paper fitted bulk velocities to the 8 vents, between 580 m/s and 1.34 km/s.
Modeling estimates for ion velocities inside the plume ranged between less than 1 km/s to 3 km/s.
Negative ions were presumed to be stationary relative to Enceladus due to the local production and short lifetimes of the molecules. However during the studied flybys a range of valid ion velocities exist, where the negative ions would be detected in the same energy bin of ELS. For example during E5 the maximum possible OH- ion velocity was 300 m/s, the deceleration caused by an electric field of -10 µV/m would be approximately 60 m/s^2, requiring only 2.5 s to achieve this deceleration. Comparing to the proposed lifetimes in Coates et al. (2010) of 6 s for H-, this deceleration appears reasonable. Furthermore, OH- lifetimes are likely higher than that of H- due to their higher electron affinity providing greater stability, thereby allowing greater deceleration. This could explain the velocities of negative ions during E3, with the required lifetime being 15 s.
26. ----------------------------
A model of the spatial and size distribution of Enceladus׳ dust plume
https://www.sciencedirect.com/science/article/abs/pii/S0032063314002979?via%3Dihub
Patrick Meier et al, 2014
Extracts - Major results are :
(1) due to the local plasma environment the nanograins are accelerated by the Lorentz force and form a structured tail;
(2) due to the finite charging time the peak dust charge density is located about below Enceladus׳ south pole;
(3) nanograins smaller than 10 nm are more than 99% of the produced dust;
(4) CAPS data are best matched if the nanograins are launched with high, collimated start velocities;
(5) the grain charging time is crucially affected by inhomogeneities in the local plasma environment.
----------------------------
Wiki - https://en.wikipedia.org/wiki/Enceladus
Extracts - Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, molecular hydrogen, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totaling about 200 kg/s. Some of the water vapor falls back as "snow"; the rest escapes and supplies most of the material making up Saturn's E ring. According to NASA scientists, the plumes are similar in composition to comets. Its interior is believed to be tidally heated and this seems to be driving the geological activity. At Enceladus, it appears that cryovolcanism occurs because water-filled cracks are periodically exposed to vacuum, the cracks being opened and closed by tidal stresses. The fresh, clean ice that dominates its surface makes Enceladus the most reflective body in the Solar System, with a visual geometric albedo of 1.38. Because it reflects so much sunlight, its surface only reaches a mean noon temperature of −198 C, somewhat colder than other Saturnian satellites.
Numerous fractures were found within the older, cratered terrain, suggesting that the surface has been subjected to extensive deformation since the craters were formed ... All of this indicates that Enceladus's interior is liquid today, even though it should have been frozen long ago. The November 2005 images showed the plume's fine structure, revealing numerous jets (perhaps issuing from numerous distinct vents) within a larger, fainter plume, extending out nearly 500 km from the surface of Enceladus, which is only 500 km wide. The particles have a bulk velocity of 1.25 km/s and a maximum velocity of 3.4 km/s. Cassini's UVIS later observed gas jets coinciding with the dust jets seen by ISS during a non-targeted encounter with Enceladus in October 2007.
The combined analysis of imaging, mass spectrometry, and magnetospheric data suggests that the observed south polar plume emanates from pressurized subsurface chambers, similar to Earth's geysers or fumaroles. Fumaroles are probably the closer analogy, since periodic or episodic emission is an inherent property of geysers. The plumes of Enceladus were observed to be continuous to within a factor of a few. The intensity of the eruption of the south polar jets varies significantly as a function of the position of Enceladus in its orbit. The plumes are about 4 times brighter when Enceladus is at apoapsis (the point in its orbit most distant from Saturn) than when it is at periapsis. This is consistent with geophysical calculations which predict the south polar fissures are under compression near periapsis, pushing them shut, and under tension near apoapsis, pulling them open. Much of the plume activity consists of broad curtain-like eruptions. Optical illusions from a combination of viewing direction and local fracture geometry previously made the plumes look like discrete jets.
----------------------------
Wiki - https://en.wikipedia.org/wiki/Tiger_stripes_(Enceladus)
Extracts - The tiger stripes of Enceladus consist of 4 sub-parallel, linear depressions in its south polar region. These low ridges with a central fracture and are called Sulcus (plural, sulci). The 4 tiger stripes are officially named as :
- Alexandria Sulcus
- Cairo Sulcus
- Baghdad Sulcus
- Damascus Sulcus
Baghdad and Damascus sulci are the most active, while Alexandria Sulcus is the least active. Also, the tiger stripes have elevated surface temperatures, indicative of present-day cryovolcanism on Enceladus centered on the tiger stripes.
On average, each tiger stripe depression is 130 kilometers long, 2 kilometers wide, and 500 meters deep. The flanking ridges are, on average, 100 meters tall and 2–4 kilometers wide. The tiger stripes could either be tectonic fractures or the result of fissures in Enceladus' lithosphere.
The 4 stripes are spaced approximately 35 kilometers apart. The ends of each tiger stripe differ in appearance between the anti-Saturnian and sub-Saturnian hemisphere. On the anti-Saturnian hemisphere, the stripes terminate in hook-shaped bends, while the sub-Saturnian tips bifurcate dendritically. Virtually no impact craters have been found on or near the tiger stripes, suggesting a very young surface age.
Another aspect that distinguishes the tiger stripes from the rest of the surface of Enceladus are their unusual composition. Nearly the entire surface of Enceladus is covered in a blanket of fine-grained water ice. The ridges that surround the tiger stripes are often covered in coarse-grained, crystalline water ice. Trapped carbon dioxide ice and simple organics also were detected within the tiger stripes. Simple organic material has not been detected anywhere else on the surface of Enceladus.
The hottest material near Enceladus' south pole is located within the tiger stripe fractures. Temperatures range between 113–157 K (-160.15 C to -116.15 C), significantly warmer than the expected 68 K (-205.15 C) for this region of Enceladus.
A plume of water vapour and ice, methane, carbon dioxide, and nitrogen emanates from a series of jets located within the tiger stripes. Over 100 plumes have been identified on Enceladus.
----------------------------
Saturn's moon Enceladus surprisingly comet-like
https://www.newscientist.com/article/dn13541-saturns-moon-enceladus-surprisingly-comet-like/
New Scientist, 2008
Extracts - Saturn’s curious moon Enceladus appears to have the same chemical makeup as a comet, according to the latest results from the Cassini probe. That’s a big surprise, as Enceladus should have formed in very different conditions from those of comets.
Cassini flew through the huge plume of steam and other gases that spews from fissures at the moon’s south pole & detected water vapour, carbon dioxide, methane and a range of more complex organic chemicals such as propane.
“The organics are clearly there in abundance beyond what we expected,” says INMS lead scientist Hunter Waite of the Southwest Research Institute in San Antonio, Texas, US. “And the composition is very like the composition of a comet.”
“It indicates that Enceladus and comets were made of the same initial materials, and/or affected by similar internal processes” - Cassini scientist Julie Castillo, NASA JPL
That is rather puzzling because comets are thought to have formed far from the Sun, out in the region of Uranus and Neptune, says INMS co-investigator Roger Yelle of the University of Arizona in Tucson, US. Enceladus, on the other hand, is thought to have grown within the “Saturnian subnebula” – the cloud of gas that coalesced into Saturn and its major moons.
“The temperature and pressure should have been very different, so you should get different gases,” Yelle told New Scientist.
Enceladus is almost certainly not a captured giant comet, but cometary stuff might have been incorporated into the moon. Ices from the outer solar system might have infiltrated the Saturnian subnebula, suggests William McKinnon of Washington University in St Louis, Missouri, US.
Or comets might have hit Enceladus during a period of upheaval in the solar system around 4 billion years ago called the late heavy bombardment.
During the flyby, Cassini’s infrared camera mapped the heat emissions of the south pole more clearly than before, showing that a great quantity of heat is coming out along the four fractures called “tiger stripes”. Temperatures along these stripes are higher than their surroundings by up to 90 C.
“We see on Enceladus the three basic requirements for the origin of life,” says Larry Esposito of the University of Colorado in Boulder, principal investigator of another Cassini instrument, the Ultraviolet Imaging Spectrograph (UVIS). “There is water – although it may not be liquid – plus organics and heat.”
What's going on inside Saturn moon? Geysers offer intriguing new clue.
https://www.csmonitor.com/Science/2013/0731/What-s-going-on-inside-Saturn-moon-Geysers-offer-intriguing-new-clue
CS Monitor, 2013
Now, it appears that tidal action is changing the amount of ice the region ejects as well – repeatedly opening and nearly closing four parallel, 80-mile-long "tiger stripe" fissures associated with the geysers feeding the plumes.
Stresses in Enceladus's crust overpower Saturn's gravity and widen the fissures when the moon reaches the most distant point in its orbit. At closest approach, Saturn's gravity overcomes the stresses and nearly shuts the fissures.
In the end, the team found a consistent, repeating pattern of plume brightness that shifted with Enceladus's orbital distance from Saturn.
"We were totally blown away by how much the thing varied," Hedman says. "We thought: Maybe it would be a small effect."
Instead, the team found that plume was three times brighter at the most-distant point in Enceladus's orbit than it was at closest approach to Saturn. The moon makes one trip around the planet every 1.4 days. A threefold change "is a pretty dramatic thing," he says.
"Whatever model you devise, whether it's a global ocean or a partial ocean or a more-complicated arrangement, it has to reproduce these patterns," says Dr. Spencer, who was not a member of Hedman's team.
The data suggest that when Saturn's gravity clamps down on the fissures, the particles leaving the geysers emerge at higher velocities than particles do when the fissures are wider.
The opening and closing of the fissures could act in a manner similar to changing nozzles on a garden hose, he suggests.
It's a slight trend in the data, cautions Dr. Collins, who also was not among the members of Hedman's team. "But maybe there's some fairly constant background gas pressure" that's driving the geysers associated with the fissures.
Enceladus' Warm Baghdad Sulcus
https://www.jpl.nasa.gov/images/pia11696-enceladus-warm-baghdad-sulcus
Surface patterns are identical to 67p - elephant skin like
This mosaic, obtained on Nov. 21, 2009, shows a 40-kilometer (25-mile) segment of Baghdad Sulcus and illustrates the correlation between the geologically youthful surface fractures and anomalously warm temperatures recorded in the south polar region. It shows the highest-resolution data yet of the heat leaking from the moon's interior along the tiger stripes.
The image shows that broad swaths of heat are confined to a narrow, intense region no more than a kilometer (half a mile) wide along the fracture. The thermal image also reveals that the strength of the thermal radiation varies considerably along the length of this fissure segment. The temperature along Baghdad Sulcus reached more than 180 K (-93.15 C)
[My point - the warmest temperature on Enceladus & the coldest temperature on comet 67P are the same]
The V-shaped valleys that distinguish the fissure named Baghdad Sulcus (1 of the 4 in south pole) are about 500 meters (1,600 feet) deep. The 30-degree slopes that rise along the valleys appear to be coated with smooth-looking particulate deposits that are peppered with large ice blocks that can reach tens of meters in size. The smooth materials most likely represent ice grain fallout from active jets that erupt along this warm and active section of Baghdad. The ice blocks appear to be icy rubble that may have been exposed by scouring from the eruptions, seismic shaking, and down-slope settling of the finer ice particles.
[My point - physically impossible for water ice to exist at -93.15 C or even as low as -163 C !]
The moon's south pole lies outside of the frame of the mosaic, in the darkness below what is shown here. The full-length of Baghdad Sulcus, one of the longest tiger stripes, stretches about 175 kilometers (109 miles) all the way across the south polar region. This high-resolution view focuses only on one end of the rift, in the hemisphere that always faces toward Saturn.
At the end of the Baghdad Sulcus segment shown here, a distinct branching pattern of fractures can be seen forking away from the central rift. The main fissure and the branching rifts slice through a complex system of quasi-parallel, rope-like, rounded ridges each as large as a kilometer (half a mile) across and hundreds of meters (yards) in height. At scales of tens to hundreds of meters (tens to hundreds of yards), a fine network of small parallel cracks are pervasive, slicing through the valley walls of Baghdad as well as through the ropey ridges. Near the very top of the mosaic, the ropey terrain transitions to a distinctly different zone in which a complicated network of fractures subdivides a broad plain into complex polygonal patterns created by tectonics.
The brightest colors in the map do not correspond directly to higher temperatures, but rather to a combination of higher temperatures and larger areas of warm surface material. The intensity of heat radiation increases as the color shades from violet to red to orange to yellow. No internal heat was detected in the darkest violet regions. Uncolored regions were not mapped by Cassini's composite infrared spectrometer instrument.
While the heat appears to emanate mostly from the main Baghdad tiger stripe, some of the fractures branching off or parallel to it also appear warmer and active to varying degrees.
The narrow central fissure is probably even warmer than the 180 Kelvin (minus 140 degrees Fahrenheit) detected -- possibly warm enough for liquid water in the fractures to be the source of the observed jets.
Close up infra red photo of fissure
https://www.sci.news/space/science-close-up-photos-enceladus-nasa-03348.html
Plumes at night also
https://solarsystem.nasa.gov/raw_images/311119/
New Closeup Images of Enceladus
https://spaceref.com/science-and-exploration/new-closeup-images-of-enceladus/
Cassini’s ‘Skeet Shoot’ of Enceladus Produces Spectacular Images
https://www.universetoday.com/20554/cassinis-skeet-shoot-of-enceladus-produces-spectacular-images/
Main pic shows elephant skin patterns
comments from Bill :
Amazing resolution and a tribute to image motion compensation. There is no hint of anything like a vent point source, and no debris fall from ejected material is evident. I’ll put my money on ion sputtering/current flow being the cause of the plumes, not geologic activity. The Saturnian system is well characterized as an energetic charged particle environment. The third photo clearly shows formations, that if found on Earth or Mars, would be called alluvial fans, attributed to water. Perhaps you can think that water flowed on the surface of Enceladus (I can’t, it’s way too cold, less than 80K), but these are Lichtenberg figures and the mark of an electrical discharge playing across the surface.
Tiger stripes close up
https://solarsystem.nasa.gov/resources/14190/baghdad-and-cairo-sulci-on-enceladus-labeled/
https://www.jpl.nasa.gov/news/cassini-pinpoints-source-of-jets-on-saturns-moon-enceladus
The new images, with jet source locations labeled, are available at:
http://www.nasa.gov/cassini
http://saturn.jpl.nasa.gov
http://ciclops.org
Ice blocks between 10 and 100 meters on Enceladus surface
https://www.jpl.nasa.gov/images/pia06250-boulder-strewn-surface
https://phys.org/news/2019-09-snow-cannon-enceladus-saturn-super-reflector-moons.html
https://www.vice.com/en/article/wn389w/saturn-enceladus-aliens-moon-cassini-methane
Looking down a plume to surface. No vents
https://www.universetoday.com/71296/amazing-new-close-up-images-of-enceladus/
https://nightskyonline.info/rt-maximaxoo-space-cassinis-view-down-into-a/
https://news.softpedia.com/news/nasa-releases-close-up-views-of-saturn-s-icy-moon-enceladus-494679.shtml#sgal_5
https://www.nbcnews.com/science/space/map-reveals-101-geysers-saturnian-moon-enceladus-n167096
https://www.planetary.org/space-images/enceladan-south-polar-vents-and-plumes
https://skyandtelescope.org/astronomy-news/how-moon-enceladus-got-its-stripes/
https://www.flickr.com/photos/53460575@N03/26374330133
Geysers from the Tiger Stripes of Enceladus
https://aasnova.org/2015/10/02/geysers-from-the-tiger-stripes-of-enceladus/
https://iopscience.iop.org/article/10.1088/0004-6256/150/3/96
Tiger stripes near Enceladus' south pole - no vents anywhere
https://www.planetary.org/space-images/tiger-stripes-near-enceladus-south-pole
Ridges and fractures during Nov. 21, 2009 flyby of Saturn's moon
https://www.nasa.gov/mission_pages/cassini/multimedia/cassini-b-20091121.html
https://www.nasa.gov/mission_pages/cassini/whycassini/cassini20091121.html
Thread :
http://www.collectspace.com/ubb/Forum33/HTML/000001-6.html
Artwork similar to 67P expectation
https://letsgetsciencey.com/tiger-stripes-enceladus-explained/
https://www.spaceflightinsider.com/space-centers/jet-propulsion-laboratory/cassini-linda-spilker-missions-legacy/
Baghdad Sulcus in 3-D
https://solarsystem.nasa.gov/resources/14854/baghdad-sulcus-in-3-d/
Perspective view of Baghdad Sulcus, Enceladus
https://www.jpl.nasa.gov/images/pia12208-perspective-view-of-baghdad-sulcus-enceladus
https://solarsystem.nasa.gov/resources/14861/enceladus-warm-baghdad-sulcus/
https://solarviews.com/cap/pia/PIA12207.htm
https://www.americaspace.com/2017/11/09/nasa-designs-advanced-new-selfi-instrument-to-help-search-for-life-on-enceladus/
https://www.universetoday.com/71296/amazing-new-close-up-images-of-enceladus/
https://blogs.scientificamerican.com/life-unbounded/walking-on-enceladus/
https://www.jpl.nasa.gov/images/pia12209-perspective-view-of-cairo-sulcus-enceladus
Predicted vs Observed temperature of Enceladus
https://solarsystem.nasa.gov/resources/12631/enceladus-temperature-map/
Equatorial temperature : 80 K (-193.15 C)
South Pole : 85 K (-188.15 C), 5 C warmer than equator
South Pole expected temp : 65 K (-208.15 C), 15 C colder than equator was the expectation
Tiger Stripes : 110 K (-163.15 C), 30 C warmer than equator
https://solarsystem.nasa.gov/moons/saturn-moons/enceladus/in-depth/
surface temperature : -330 F / - 201 C
the south polar region of Enceladus is almost entirely free of impact craters. The area is also littered with house-sized ice boulders
The eruptions appear to be continuous, generating an enormous halo of fine ice dust around Enceladus, which supplies material to Saturn's E-ring. Only a small fraction of the material ends up in the ring, however, with most of it falling like snow back to the moon’s surface, which helps keep Enceladus bright white.
Several gases, including water vapor, carbon dioxide, methane, perhaps a little ammonia and either carbon monoxide or nitrogen gas make up the gaseous envelope of the plume, along with salts and silica. And the density of organic materials in the plume was about 20 times denser than scientists expected.
The E ring is mostly made of ice droplets, but among them are peculiar nanograins of silica, which can only be generated where liquid water and rock interact at temperatures above about 200 F / 90 C. This, among other evidence, points to hydrothermal vents deep beneath Enceladus’ icy shell, not unlike the hydrothermal vents that dot Earth’s ocean floor. (but depth of speculated ocean on enceladus 10 km, avg depth of earth ocean is only 3km. warm thermal currents driving up liquid water to surface & ejecting it thru the ice shell at supersonic velocities, without a single vent on the surface is ridiculous fantasy ! logic & evidence is no longer needed for religious priests masquerading as scientists)
Enceladus Near-Fissure Surface Temperatures
https://ui.adsabs.harvard.edu/abs/2013DPS....4541601H/abstract
Robert Howell et al, 2013
We have found that including the surface sublimation cooling suppresses the higher temperatures. Regardless of the fissure temperature, surface temperatures above 200K can only be maintained by conduction within a few tens of centimeters of the assumed fissure wall. The high sublimation erosion rates (0.25 m/yr at 180K, rising to over 100 m/yr at 220K) imply that the fixed boundaries we have previously assumed are unrealistic. If these surface temperatures are maintained then either a sublimation lag of non-ice components will accumulate, inhibiting sublimation, or the geometry of the fissure vent will rapidly change.
Enceladus’ near-surface CO2 gas pockets and surface frost deposits
https://www.sciencedirect.com/science/article/abs/pii/S0019103517302506
Dennis Matson et al, 2018
Solid CO2 surface deposits were reported in Enceladus’ South Polar Region by Brown et al. (2006). They noted that such volatile deposits are temporary and posited ongoing replenishment. Gas pocket venting is episodic compared to the more or less continuous eruptive plumes, emanating from the “tiger stripes”, that are supported by plume chambers. Two styles of gas pocket venting are considered: (1) seeps, and (2) blowouts.
Sustained eruptions on Enceladus explained by turbulent dissipation in tiger stripes
https://arxiv.org/abs/1606.00026
Edwin Kite et al, 2016
Detailed paper
Enceladus Notes 2
https://thoughtprovokingvinny.blogspot.com/2023/03/enceladus2.html
The detection of sodium salts (mainly NaCl) in the ice grains ejected in the plume indicates that this material originates from an ocean in contact with Enceladus' rocky core. Plume is likely a long-lived phenomenon that could be sustained for tens of millions to billions of years.
If ice shell is thinner at south pole, that means the ocean is deepest there.
Fig 2 : thickness of ice shell & depth of ocean is different here
Silica nanograins can most plausibly be inferred to have been generated from hot (>90 °C) mineral-laden waters formed by hydrothermal leaching of silicate minerals issuing from the sea floor and immediately condensing into a colloid upon meeting the cold (∼0 °C) ocean water. Once formed, those nanoparticles are transported from the sea floor up through the ocean to the fractures in the ice shell by convection and/or diffusive upwelling and then, by other processes such as pressure-driven upward movement, to the top of the water column, where they are incorporated into the ejected ice grains that join Saturn's E ring.
Volatile exsolution, boiling, and any turbulence in the liquid-filled conduits leading from the ocean to the surface would create bubbles that could scavenge organic material and even microorganisms via attachment to the bubbles' surfaces as they rise. The organics and cells would then be released in a spray when the bubbles burst at the water's upper surface (Porco et al. 2017). On Enceladus, the evaporating water vapour would presumably freeze upon encountering the vacuum of space.
-----------------------------------
Postberg et al. 2009
Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus
https://scholar.google.com/scholar?q=Postberg+F.%2C+Kempf+S.%2C+Schmidt+J.+et+al.+2009+Natur+459+1098
Abstract : Saturn's moon Enceladus emits plumes of water vapour and ice particles from fractures near its south pole, suggesting the possibility of a subsurface ocean. Siliceous components, identified in many ice grains, could be evidence for interaction between Enceladus’ rocky core and liquid water.
--------------------------------------
Postberg et al. 2011
A salt-water reservoir as the source of a compositionally stratified plume on Enceladus
Abstract : The discovery of a plume of water vapour and ice particles emerging from warm fractures raised the question of whether the plume emerges from a subsurface liquid source, or from the decomposition of ice. Previous compositional analyses of particles injected by the plume into Saturn's diffuse E ring have already indicated the presence of liquid water, but the mechanisms driving the plume emission are still debated. Whereas previous Cassini observations were compatible with a variety of plume formation mechanisms, these data eliminate or severely constrain non-liquid models and strongly imply that a salt-water reservoir with a large evaporating surface, provides nearly all of the matter in the plume.
----------------------------------------
Study explains how Enceladus ejects particles from oceans beneath its surface (Feb 2023)
https://phys.org/news/2023-02-enceladus-ejects-particles-oceans-beneath.html
The silica particles that Enceladus ejects begin their journey at the sea floor, far beneath the moon's surface. A new study led by UCLA scientists offers some answers. The research shows that tidal heating in Enceladus' rocky core creates currents that transport the silica, which is likely released by deep-sea hydrothermal vents over the course of just a few months. The scientists constructed a theoretical model that could account for the silica's transport across the ocean.
"Our research shows that these flows are strong enough to pick up materials from the seafloor and bring them to the ice shell that separates the ocean from the vacuum of space," Schoenfeld said. "The tiger-stripe fractures that cut through the ice shell into this subsurface ocean can act as direct conduits for captured materials to be flung into space.
Cassini found substantial amounts of hydrogen gas in the plumes which, together with the silica, present compelling evidence for hydrothermal activity at the ocean floor.
"Our model provides further support to the idea that convective turbulence in the ocean efficiently transports vital nutrients from the seafloor to ice shell," said second author Emily Hawkins, a UCLA alumna who is now an assistant professor of physics at Loyola Marymount University.
------------------------
Is the Ocean of Enceladus in a Primitive Evolutionary Stage? (Feb 2022)
https://www.intechopen.com/chapters/81850
---------------------------
THE COMPOSITION AND HABITABILITY OF ENCELADUS’ OCEAN
- LM Fifer, LPSC 2020
https://www.hou.usra.edu/meetings/lpsc2020/pdf/2727.pdf
--------------------------------
Liquid water on Enceladus from observations of ammonia and 40Ar in the plume
https://www.nature.com/articles/nature08153
The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180 K (-93 C) have been measured near the fractures from which the jets emanate.
The comet-like DH water ratio provides definitive evidence that Enceladus accreted from planetesimals formed in the solar nebula rather than in an initially dense, warm subnebula. In addition to the D/H ratio, Enceladus’ plume displays other striking compositional similarities to cometary comae.
Figure 3 - The abundances of CO2,CH4,C2H2,NH3 and H2CO (relative to H2O) in the Enceladus plume resemble those in comets, suggesting that these abundances are typical of well-mixed outer Solar System material. The Enceladus plume may contain proportions of CH3CHO and HCN that are somewhat elevated compared to comets. In contrast, the plume H2S and CH3OH abundances are significantly lower than those in comets. The most conspicuous difference is the deficiency of native CO relative to that produced in the instrument and the ubiquity (common presence of) of N2/C2H4 in the plume. These features are puzzling, because CO is generally the most abundant non-H2O volatile in comets (observed range 0.4–20%), and neither N2 nor C2H4 has been detected in comets.
Points on both CO & N2 are wrong. Both ingredients have been detected in comet 67P plumes.
---------------------------------------
Cassini ion and neutral mass spectrometer: Enceladus plume composition and structure
http://www.igpp.ucla.edu/public/mkivelso/refs/PUBLICATIONS/1121290Waite.pdf
------------------------------------------
Plume and surface composition of Enceladus
https://ui.adsabs.harvard.edu/abs/2018eims.book..129P/abstract
------------
Cassini Observes the Active South Pole of Enceladus (2006)
Carolyn Porco et al
https://web.mit.edu/wisdom/www/porco-enceladus.pdf
ISS images show that the tiger stripes are linear depressions, typically about 500 m deep, 2 km wide, and 130 km in length, flanked on both sides by prominent 100-m-high ridges. Darker material extends a few kilometers to either side. They are spaced 35 km apart and have similar shapes and orientations. In the anti-Saturn hemisphere, tiger stripes often terminate in prominent hook-shaped bends, but in the sub-Saturn hemisphere, they progressively bifurcate into crudely dendritic patterns.
The spectrophotometry of the SPT is unusual on Enceladus. At low phase, the bright plains in between the tiger stripes are 10% brighter than the average reflectivity of Enceladus; the contrast between these units and the tiger stripes is 20% and the greatest seen on Enceladus. These distinct properties may be directly related to the geologic activity, present-day venting, and particle fallout ongoing in this region.
ISS broadband spectra of all South Pole Terrain (SPT) materials are consistent with a composition of pure water ice.
There are 2 basic possibilities for the source of the jets: either sublimating ice, above or below ground, or underground reservoirs of boiling liquid erupting through vents in the tiger stripes. The former operates at temperatures below 273 K (0 C); the latter operates above 273 K (0 C).
The large ice/gas ratio argues strongly against ice condensing out of vapor, as would be expected for the sublimating ice model: The entropy change when the vapor condenses is 20 times the entropy change when the same amount of vapor expands, so only a small fraction of the vapor can condense during an adiabatic expansion.
The grains could be embedded in the ice from the start and get entrained in the flow, like the dust grains in a comet, but this seems unlikely. The grains in comets are refractory and eventually cover the comet’s surface with a dark crust. In contrast, the surface of Enceladus is bright and is mostly water ice.
In particular, the spectrum of the plains between the tiger stripes indicates that the plume particles falling back onto the surface must be water ice.
On the other hand, there is no problem forming particles from a boiling liquid. A liquid boils when the pressure drops below its saturation vapor pressure. The erupting mixture of vapor and liquid—or, in the case of Enceladus, vapor, liquid, and ice particles—is like a cold Yellowstone geyser.
Ammonia-water mixtures, although liquid down to 175 K (-98 C), are ruled out as sources because the almost pure ammonia composition of the vapor is inconsistent with the observations. Therefore, any boiling liquid/geysers must involve pure water at 273 K (0 C) or above. (Ammonia-water mixtures may be circulating underground and thermally conducting heat to the surface, keeping the tiger stripes warm, but these fluids cannot be venting to the surface.)
The boiling liquid can produce a cloud of gas and ice if some of the liquid is carried along with the vapor and freezes as it expands out of the vent... If this pressure is released (e.g.,when a crack forms in the ice), bubbles of vapor form and the liquid freezes.
The heat of fusion goes into heat of vaporization. Although the mixture is then mostly ice, its volume per mole is 24,000 times that of liquid water. In contrast, the expansion in a Yellowstone geyser is only a factor of 10, and the water comes out as a frothy mixture.
When released from pressure, the source fluid will accelerate out of the vent as an ice/gas mixture. The geometry of the vent determines the angle of emergence and what fraction of the ice is in micrometer-sized particles. A gas expanding into vacuum reaches sonic speed, which for water vapor at 273 K (0 C) is twice the escape velocity. Even water vapor at 200 K (-73 C) can accelerate micrometer sized particles to escape velocity.
For these reasons, we favor the boiling liquid model over the sublimating ice model. On the basis of pressure arguments alone, the liquid chambers giving rise to Enceladus’ geysers could be as close as 7 m to the surface.
In this model, heating large enough to raise the temperature to 273 K might be provided by very localized, near-surface tidal and/or librational frictional heating operating on and within the tiger stripe fractures.
Although no instrument has positively detected ammonia, its existence cannot be ruled out: The derived upper limiting value to the ammonia abundance [0.5% in the plume vapor could still permit a geophysically important amount of ammonia at depth, although, as discussed above, an ammonia-water mixture cannot be venting to space.
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