The Science Case for a Return to Enceladus
https://www.researchgate.net/publication/353394968_The_Science_Case_for_a_Return_to_Enceladus
Morgan Cable et al, 2021 (includes Carolyn Porco)
The plume is formed, in part, by about 100 jets erupting from four main surface fissures, the “Tiger Stripes” in the South Polar Terrain (Porco et al. 2014); material may also be erupting from these fissures in the form of sheets (Porco et al.2014; Spitale et al. 2015). The detection of sodium salts (mainly NaCl) is covered in Postberg et al. 2009,2011.
There is diurnal variation in the plume’s brightness (and hence mass). Plume is likely a long-lived phenomenon that could be sustained for tens of millions to billions of years.
Two independent lines of evidence show that the plume’s subsurface water reservoir is not a regional sea but a global ocean :
1) gravity measurements indicate that Enceladus is not in hydrostatic equilibrium, and that it requires isostatic compensation to fit the gravity field and excess topography.
2) Enceladus’ rotation has a forced physical libration (wobble) too large to be consistent with an icy shell grounded to the rocky core, again only possible if there is a global ocean.
Three key discoveries strongly support the occurrence of contemporary hydrothermal processes at the interface between the ocean and the core of Enceladus - the plumes contained :
1) Silica nanograins
2) High levels of methane (CH4 gas)
3) Molecular hydrogen (H2 gas)
All 3 are present in the plumes of comet 67P (4 km) also. Does it also have a 10 km deep sub-surface ocean ?
1
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 and are subsequently released by sputter erosion due to high energy magnetospheric particles.
2
According to modeling, the relative proportions of measured volatiles are unlikely without a gas input. For example, methane should be preferentially trapped in clathrate hydrates (water-ice cages) and therefore depleted in the plume. One plausible explanation is hydrothermal activity, which could release sufficient methane to match observed levels.
3
The third piece of evidence is identification by INMS of molecular hydrogen (H2) in the plume during a “deep dive” flyby (E21, the 21st Cassini flyby of Enceladus) at an altitude of only 48 km above Enceladus’ surface. Molecular hydrogen is a product of the oxidation of reduced iron (Fe(0), Fe(II)) by water. The most familiar process that drives H2 production on Earth is serpentinization, a rock alteration process that can occur in a subset of submarine hydrothermal systems where liquid water interacts with ultramafic rocks (igneous rocks with high Mg and Fe contents). Thus, this evidence further suggests that the ocean of Enceladus is in contact with, and reacting with, its rocky core through hydrothermal processes.
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 micro-organisms 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.
On Earth, the most energetic spray can be lofted into the atmosphere; on Enceladus, it would presumably freeze upon encountering the vacuum of space and generate many, if not most, of the larger organic- and salt-rich icy particles forming the plume.
A result of this scavenging process is that the less energetic spray that falls back to the water’s surface, as well as the bubbles that fail to burst, can under certain conditions form an organic-rich film at the top of the water column, similar to the sea surface microlayer seen on Earth’s oceans, especially after a storm. In the cold polar regions on Earth, the wind-induced bursting of air bubbles at the sea surface microlayer generates a sub-micron sea spray aerosol containing ice particles that are organic-rich and salt-poor. These ice particles are similar in organic and salt content to the organic-rich plume grains detected by Cassini.
Slow dust in Enceladus' plume from condensation and wall collisions in tiger stripe fractures
https://www.nature.com/articles/nature06491
Considerably smaller velocities for the grains than for the vapour, has been difficult to understand. The gas and dust are too dilute in the plume to interact, so the difference must arise below the surface.
Here we report a model for grain condensation and growth in channels of variable width. We show that repeated wall collisions of grains, with re-acceleration by the gas, induce an effective friction, offering a natural explanation for the reduced grain velocity. We derive particle speed and size distributions that reproduce the observed and inferred properties of the dust plume.
The gas seems to form near the triple point of water; gas densities corresponding to sublimation from ice at temperatures less than 260 K (-13 C) are generally too low to support the measured particle fluxes. This in turn suggests liquid water below Enceladus’ south pole.
Scientists plumb the depths of the world's tallest geyser
https://www.sciencedaily.com/releases/2021/03/210315160708.htm
Depth : 100 m at least
Height of geyser : 110 m
When Steamboat Geyser, the world's tallest, started erupting again in 2018 in Yellowstone National Park after decades of relative silence, it raised a few tantalizing scientific questions. Why is it so tall? Why is it erupting again now? And what can we learn about it before it goes quiet again?
"We scientists don't really know what controls a geyser from erupting regularly, like Old Faithful, versus irregularly, like Steamboat," says Fan-Chi Lin, an associate professor with the Department of Geology and Geophysics. "The subsurface plumbing structure likely controls the eruption characteristics for a geyser. This is the first time we were able to image a geyser's plumbing structure down to more than 325 feet (100 m) deep."
Meet Steamboat Geyser
If you're asked to name a Yellowstone geyser and "Old Faithful" is the only one that comes to mind, then you're past due for an introduction to Steamboat. Recorded eruption heights reach up to 360 feet (110 m), tall enough to splash the top of the Statue of Liberty.
"I already knew that Steamboat was the tallest active geyser in the world, but seeing it in major eruption blew me away", says Jamie Farrell, a research assistant professor with the University of Utah Seismograph Stations.
Plumbing the depths
The results showed that the underground channels and fissures that comprise Steamboat Geyser extend down at least 450 feet (140 m). That's much deeper than the plumbing of Old Faithful, which is around 260 feet (80 m).
"This finding rules out the assumption that the two features are connected with something like an open pipe, at least in the upper 140 meters," says Sin-Mei Wu, a recently graduated doctoral student working with Lin and Farrell. That's not to say that the two features are totally separate, though. The fact that the pool drains when Steamboat erupts suggests that they are still connected somehow, but probably through small fractures or pores in the rock that aren't detectable using the seismic signals the researchers recorded. "Understanding the exact relationship between Steamboat and Cistern will help us to model how Cistern might affect Steamboat eruption cycles," added Wu.
https://en.wikipedia.org/wiki/Steamboat_Geyser
Steamboat's major eruptions generally last from 3 to 40 minutes (several durations surpassing an hour were observed during the 2018 active phase[6]), and are followed by powerful jets of steam. During these eruptions, water may be thrown more than 300 feet (91 m) into the air.
Steamboat does not erupt on a predictable schedule, with recorded intervals between major eruptions ranging from three days to fifty years. The geyser was dormant from 1911 to 1961. In 1964, twenty-nine eruptions were reported,[8] setting the record for the most eruptions within a calendar year. In 2018, the geyser began a prolonged period of frequent activity lasting through at least 2022, with more than 40 eruptions recorded annually in both 2019 and 2020.
Minor eruptions of 10 to 15 feet (3.0 to 4.6 m) are much more frequent.
After an eruption, the geyser often vents large amounts of steam for up to 48 hours. Sometimes during this part of an eruption, water may return to Steamboat, causing it to jet water once again, though to lesser heights.[6] Cistern Spring, located nearby, will drain completely following a major eruption of the geyser; the spring refills within a few days.
The most recent eruption of Steamboat Geyser occurred on January 28, 2023. This was the 161st eruption since it re-activated in early 2018. In 2019 the 48th eruption occurred on December 26th. That set a new record for the most eruptions within a calendar year. The calendar year 2020 also saw 48 eruptions, tying the record set in 2019.
Spacecraft Data Suggest Saturn Moon's Ocean May Harbor Hydrothermal Activity
https://www.nasa.gov/press/2015/march/spacecraft-data-suggest-saturn-moons-ocean-may-harbor-hydrothermal-activity
NASA, 2015
An extensive 4 year analysis of data from the spacecraft, computer simulations and laboratory experiments led researchers to the conclusion the tiny grains most likely form when hot water containing dissolved minerals from the moon's rocky interior travels upward, coming into contact with cooler water. Temperatures required for the interactions that produce the tiny rock grains would be at least 90 degrees Celsius.
"It's very exciting that we can use these tiny grains of rock, spewed into space by geysers, to tell us about conditions on -- and beneath -- the ocean floor of an icy moon," said the paper’s lead author Sean Hsu, a postdoctoral researcher at the University of Colorado at Boulder.
Cassini's cosmic dust analyzer (CDA) instrument repeatedly detected miniscule rock particles rich in silicon, even before Cassini entered Saturn’s orbit in 2004. By process of elimination, the CDA team concluded these particles must be grains of silica, which is found in sand and the mineral quartz on Earth. The consistent size of the grains observed by Cassini, the largest of which were 6 to 9 nanometers, was the clue that told the researchers a specific process likely was responsible.
On Earth, the most common way to form silica grains of this size is hydrothermal activity under a specific range of conditions; namely, when slightly alkaline and salty water that is super-saturated with silica undergoes a big drop in temperature.
"We methodically searched for alternate explanations for the nanosilica grains, but every new result pointed to a single, most likely origin," said co-author Frank Postberg, a Cassini CDA team scientist at Heidelberg University in Germany.
The extremely small size of the silica particles also suggests they travel upward relatively quickly from their hydrothermal origin to the near-surface sources of the moon's geysers. From seafloor to outer space, a distance of about 30 miles (50 kilometers), the grains spend a few months to a few years in transit, otherwise they would grow much larger.
The team found that, at the high pressures expected in the moon's ocean, icy materials called clathrates could form that imprison methane molecules within a crystal structure of water ice. Their models indicate that this process is so efficient at depleting the ocean of methane that the researchers still needed an explanation for its abundance in the plume.
In one scenario, hydrothermal processes super-saturate the ocean with methane. This could occur if methane is produced faster than it is converted into clathrates. A second possibility is that methane clathrates from the ocean are dragged along into the erupting plumes and release their methane as they rise, like bubbles forming in a popped bottle of champagne.
Philae's Real-Time Descent and Enceladus's Global Ocean
https://blogs.scientificamerican.com/life-unbounded/philae-s-real-time-descent-and-enceladus-s-global-ocean-video/
Dr. Caleb Scharf, astrobiology scientist, NASA, 2015
"The position of features in hundreds of Cassini images has allowed the researchers to track these librations. They've discovered that the back and forth wobbles of this moon (about 0.12 degrees in amplitude) are much larger than they should be if most of the interior were solid ice or rock"
[ Me : But scientists also claim that ice at those temperatures is hard as rock. So how can a 40 km thick hard-as-rock ice shell flex & wobble repeatedly ? ]
"Good evidence already exists for some kind of liquid water 'pocket' towards Enceladus's south pole - where it regularly erupts with plumes of water ice and other compounds that suggest a deeper hydrothermal system - but the excess wobble of the whole moon now indicates that there is in fact a global ocean."
"This body of liquid, likely composed of salt-rich water, helps disconnect the icy crust from the core of the moon, and allows for the big librations seen in the measurements. It could be some 30-40 kilometers in depth, starting perhaps 10 or 20 kilometers below the surface."
"It's a very exciting result, an extra feather in the cap for Enceladus as a prime target to search for life in the solar system. It also raises an intriguing puzzle as to how this ocean is kept warm."
The gas & dust plumes of of 500 km Enceladus are very similar to those of the 4 km wide comet 67P - in appearance, composition & behaviour, suggesting a common mechanism. This comet is much nearer & easier to reach. How come it is not considered as a prime target to search for life ?
Salty, Alkaline Curtains are Erupting from Enceladus – and That’s Good
https://blogs.scientificamerican.com/life-unbounded/salty-alkaline-curtains-are-erupting-from-enceladus-8211-and-that-8217-s-good/
Dr. Caleb Scharf, astrobiology scientist, NASA, 2015
"This active cryovolcanism seems to point to a subsurface ‘pocket ocean’ (less kindly we might call it a lake) towards the southern polar regions of Enceladus. As time goes by, more and more evidence is accumulating to suggest that this internal body of water has been – and perhaps still is – in direct contact with a rocky, mineral-rich, core."
"This ‘soda ocean’ should be strongly alkali too – with a pH of 11 to 12. How does it get to be this way? If terrestrial oceans are a good proxy then these conditions suggest a process called serpentinization, where raw mantle material rich in iron and magnesium reacts with water. The scientists also point out a highly desirable side-effect of serpentinization – the production of molecular hydrogen which could serve as a potent energy source for analogs to Earth’s microbial fauna living in abyssal realms."
"A new study published in Nature by Spitale et al. takes a clever and contrarian look at the famous geysers and argues that instead of ‘jets’ of material, in many cases these are much more likely to be sheets or curtains erupting along the great tiger-stripe cracks at the moon’s southern end."
[ Curtain eruptions from Enceladus' south-polar terrain
https://www.nature.com/nature/journal/v521/n7550/full/nature14368.html ]
"In a nutshell, curtain-like eruptions can play optical tricks on the observer – in this case the Cassini images. Viewing angles and the wiggly geometry of the surface cracks can conspire to enhance the brightness of the material along vertical directions, presenting an illusion of bright jets – the way a wavy curtain can appear to have vertical stripes."
"If correct, this means that we can get a better handle on the physical conditions that create these outbursts. The nature of the sheets or curtains relates to how this watery vapor is being primed beneath the surface, whether in smaller or larger cave-like cavities above the interior ocean for example."
Cassini Reveals That Enceladus Is Embraced by a Web of Cracks
https://blogs.scientificamerican.com/life-unbounded/cassini-reveals-that-enceladus-is-embraced-by-a-web-of-cracks/
Dr. Caleb Scharf, astrobiology scientist, NASA, 2015
"Other areas on the moon's surface were known to be covered in a network of cracks or fissures in the ice. Now it appears that these features extend all the way to the far north, and they exhibit a remarkable pattern of thin 'slice' like crevices in close packed arrays. The north of Enceladus is also more heavily cratered - suggesting a slightly older region that hasn't been 'refreshed' by cryovolcanism or ice tectonics. But the web-like networks of cracks appear to overlay - or be embedded in - the crater features in most cases."
Compare pic of Ence vs 67p surface of slices + elephant skin matches
"... these features extend all the way to the far north, and they exhibit a remarkable pattern of thin 'slice' like crevices in close packed arrays"
"Other areas on the moon's surface were known to be covered in a network of cracks or fissures in the ice. Now it appears that these features extend all the way to the far north, and they exhibit a remarkable pattern of thin 'slice' like crevices in close packed arrays ... But the web-like networks of cracks appear to overlay - or be embedded in - the crater features in most cases"
[ Are the water vapor plumes of Enceladus due to liquid water getting exposed to space or are they being blasted off directly from the vents on the floor of the subsurface ocean ? ]
https://twitter.com/caleb_scharf/status/852623829964922880?s=20 (Caleb - my analysis of new Cassini results)
New Evidence for Hydrothermal Havens in Enceladus
https://blogs.scientificamerican.com/life-unbounded/new-evidence-for-hydrothermal-havens-in-enceladus/
https://twitter.com/caleb_scharf/status/723900885412229120?s=20
Why Enceladus is not higher on list is beyond me (on chart of sciam about where we will find life)
https://www.scientificamerican.com/article/beyond-earth-day-where-will-alien-life-be-discovered-first/
https://twitter.com/caleb_scharf/status/426070453841444865?s=20
Enceladus, Europa, and now Ceres - all spouting water plumes
https://twitter.com/caleb_scharf/status/47652422616760320?s=20
Springtime on Enceladus (Anonymous Caleb)
http://lifeunbounded.blogspot.com/2011/03/springtime-on-enceladus.html
Water Erupts Across the Solar System : what's going on with Europa, Enceladus and Ceres
https://blogs.scientificamerican.com/life-unbounded/water-erupts-across-the-solar-system/
https://twitter.com/caleb_scharf/status/596362467128844288?s=20
New Enceladus studies point towards a soda ocean erupting in curtains
https://blogs.scientificamerican.com/life-unbounded/salty-alkaline-curtains-are-erupting-from-enceladus-8211-and-that-8217-s-good/
101 Geysers Point To Enceladus' Deep Ocean
https://blogs.scientificamerican.com/life-unbounded/101-geysers-point-to-enceladus-deep-ocean/
Cassini final close flyby reveals further exquisite details of the surface terrain
https://blogs.scientificamerican.com/life-unbounded/walking-on-enceladus/
https://twitter.com/caleb_scharf/status/575735173226106881?s=20
2015 - Silica particles from Saturn's E-ring could have originated as ice-shrouded specks from hydrothermal systems inside Enceladus
https://twitter.com/caleb_scharf/status/45525360724557824?s=20
Cassini finds Saturn's moon Enceladus is a powerhouse
https://www.sciencedaily.com/releases/2011/03/110308144714.htm
Europa
https://blogs.scientificamerican.com/life-unbounded/europa-three-more-clues/
Europa Gives Up Some Of Its Secrets
https://blogs.scientificamerican.com/life-unbounded/europa-gives-up-some-of-its-secrets
Earth's water
https://www.scientificamerican.com/article/the-enduring-mystery-of-earths-water/
Enceladus, Europa, Ganymede, etc may all have, or have had, large oceans of liquid water trapped beneath a frozen crust.
https://blogs.scientificamerican.com/life-unbounded/have-we-got-solar-system-habitability-backwards
Comet 67P
https://blogs.scientificamerican.com/life-unbounded/rosetta-captures-stunning-new-images-of-comet-8217-s-surface-and-activity/
Caleb's pseudoscience - "Jets of SUBLIMATED material are already streaming off the surface"
Comet 67P
https://blogs.scientificamerican.com/life-unbounded/the-surreal-task-of-landing-on-a-comet/
Caleb's pseudoscience - "... here's 67P in full, with a hint of the out-gassing that's occurring from the 'neck' of the nucleus as volatiles SUBLIMATE away, carrying dust into interplanetary space"
Death of comet ISON
https://blogs.scientificamerican.com/life-unbounded/will-this-be-the-comet-of-the-century/
Caleb's pseudoscience - "Increasing solar irradiation warms their surfaces and SUBLIMATES components like solid water and carbon dioxide - creating great tails of reflecting gas and glowing ions, along with streams of dusty carbon compounds and silicates."
Death of comet ISON (not Caleb)
https://www.scientificamerican.com/article/comet-ison-what-we-learned/
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