Though NASA’s Cassini orbiter has been surveying Saturn and its moons in stunning detail for the past five years, it missed -- not surprisingly
-- the 800-pound gorilla in the Saturnian system.
Infrared astronomers announced yesterday the discovery of a huge puffy and tenuous ring of ice and dust
encircling Saturn well beyond the orbits of most of its satellites.
The ghostly ring is way too faint to be seen with optical telescopes. It took the infrared eyes of NASA’s Spitzer Space Telescope to pick up the telltale glow of warm dust in the ring. The ring sets a new record as the largest
structure seen around any planet.
If Saturn were to have any inhabitants, they’d be
celebrating today.
Today is Saturn’s equinox, which means the sun is shining
directly over the edge of Saturn’s rings, which are coplanar. This means the
rings are casting a comparatively pencil-thin shadow across the planet’s cloud tops. As seen
from Earth the rings momentarily vanish because the have no sunlight to
reflect.
This happens every 14.5 years during Saturn’s 29-year long
orbit. Though Galileo didn’t recognize Saturn’s ear-like appendages as rings,
he was the first to record that that they would mysteriously disappear. “God
has tricked me,” he wrote.
If aliens sent a probe to do a flyby of Earth they might be
surprised to discover that beauty is only skin deep. I’m talking about our
oceans that cover two-thirds of the planet. The probe would measure Earth’s
mass, and alien scientists would easily calculate that Earth has the density of
rock. In other words the oceans are just a thin veneer over a ball of
rock and molten iron.
But we have two true “aqua-planets” under our nose that are
at last revealing themselves. And, when things get damp, life seems to rear its head.
It was recently reported that Saturn’s giant moon Titan is a
soggy world. Measurements by the NASA/ESA Cassini probe show that Titan is squashed
like an under inflated soccer ball. It bulges at the middle and is flatter at
the poles by about 2,000 feet as compared to the equator.
The fact that Titan is not perfectly round strongly suggests Titan
may hide vast reserves of liquid methane beneath its surface that make the giant moon "squishy." This would
explain Titan’s “Land-O’-Lakes” topology near the poles, where methane or
ethane lakes dot the landscape. Simply put, Titan is swampy at the lower elevation
poles where the methane seeps out. Large subsurface reservoirs of liquid
hydrocarbons have long been suspected of replenishing the methane in Titan's atmosphere, where sunlight breaks apart methane.
But how do you squash a moon? One explanation is that Titan
was once closer to Saturn. Titan also would have had to spin faster to be in synchronization
with its shorter orbital period so that it could be tide-locked on Saturn
(which would be expected of a moon buried deep in Saturn’s gravitational
field). An orbit 23% closer than Titan’s present orbit would account for the
extra squashing at the poles and bulging at the equator. But what would have
caused the moon to change zip code?
The dwarf planet Ceres, biggest member of the asteroid belt,
is also fat around the middle. This too means a damp mantle that is at least
one-quarter water ice. That would be greater in volume than all the fresh water on Earth.
As with Titan, if there is liquid in the interior, it might have migrated to the surface. The water would have also carried minerals along with it. This perhaps caused the mottled pattern
seen by the Hubble and Keck telescopes.
Infrared spectroscopy of Ceres’ surface suggests it has a
crust of carbonates, clays and other water-modified minerals. These would have
been deposited long ago when the asteroid was warm enough for near-surface
liquid water.
What’s more, there may have been a substantial amount of ammonia
that had been mixed with the original water ice chunks that formed Ceres. There is a chance that the bottom part of its outer ice layer might still
be liquid today day, because ammonia makes excellent antifreeze. Titan is
also thought to have subsurface liquid water/ammonia ocean.
Even more importantly, an ammonia-water mix might be a
workable soup for incubating life. In fact ammonia has some chemical
similarities with water. There is a whole system of organic and inorganic chemistry
that takes place in ammonia. Ammonia also dissolves most organics as well as or better than water.
So two dwarf planet class bodies are so soggy, they may be homes for microbial life. NASA’s Dawn spacecraft arrives at Ceres in 2015, and we’ll
get more clues to the mini-planet’s history. Meanwhile, Cassini continues
sending back surprises from Titan. Cassini's next Titan flyby is only 12 days away.
I recently had fun making a baking soda powered tabletop
volcano to the delight of my grandson Leo, who just loves watching the thing
explode. You know, that popular middle school science fair project where vinegar (acetic
acid) neutralizes baking soda and causes it to give off carbon dioxide,
creating pressure that blows the liquid up a toy volcano cone.
But on other planets there may really be volcanoes gushing out water rather than molten rock. And, mud volcanoes that belch out a slurry of
organic-rich material, if not subterranean microbes.
The possible discovery of wet slushy volcanoes on Titan and
Mars, and damp soils, is ratcheting up the possibility of finding extraterrestrial
life. A number of papers were presented last week at the 40th Lunar and
Planetary Science Conference in The Woodlands, Texas.
Cryovolcano
In the frigid outer solar system, where daytime temperatures
are at -300 degrees Fahrenheit or lower, a different type of geology may be taking
place – cryovolcanos. These mountains are suspected of spewing out a Slurpee of ice, propane, butane and other
liquid hydrocarbons.
The best candidate is an area known as Hotei Arcus, thought
not everyone agrees it is really a volcano. Photos on different flybys taken by
the NASA/ESA Cassini orbiter have been interpreted as cryo-lava outflows.
The
lobe-like fingers, each hundreds of feet high, have a shape and thickness
consistent with highly viscous lava on Earth. Like an advancing flow of lava,
the lobes also appear to cut off several small streams apparently carved by
liquid methane.
You need a subterranean heat source close to liquid reservoirs
to spew out this stuff. It’s sort of nature’s recreation of the famous 1952 Miller-Urey
experiment that mixed pre-biotic compounds, such as water, methane and ammonia
(an ideal antifreeze for Titan) to make amino acids – the building block of
life.
Mud Volcanoes
Closer to home, Mars orbiting spacecraft have identified
dozens of mounds in the northern plains that bear a striking
resemblance to mud volcanoes on Earth. High-resolution images reveal small
knobs or patches. They frequently have one or more craters and an irregular
shape.
As on Earth, a mud volcano would form when pressurized gas
and water from as much as several miles down, blows out the surface like a
popped Champaign cork. This shoots out a gooey mess of water, mud, rocks, as
well as methane.
Mud volcanoes would
accomplish what a martian drilling rig would have a tough time doing,
transporting rocks from several miles beneath the martian surface, and placing them
within reach of sample-return rovers.
Microbial life could be flourishing deep below the martian surface,
perhaps driven there as surface conditions became hostile over geologic time. It may be warm enough miles below the surface for water to remain a liquid. The
volcanoes, which may be as young as 10 million years, offered an elevator for
microbes to reach the surface – in a martian twist on the closing chapter of Jules
Verne’s 1864 novel Journey to the Center of The Earth.
Briny Droplets
A highly publicized surprise from NASA’s Mars Phoenix Lander
was the discovery of perchlorates in the planet’s arctic region. Perchlorate is
the stuff used to make rocket fuel and explode fireworks. On Mars these salts
could keep water in a liquid state at temperatures of -160 degrees Fahrenheit.
Pockets of brine might form when the perchlorate mixes with
the water ice that Phoenix found near the north pole. In fact there has been a lively
debate whether Phoenix photographed briny liquid water droplets on the lander legs,
which would have been kicked up by its landing thrusters. Some scientists think they move like a liquid in successive exposures. Others say it’s just
frost.
The perchlorates may explain why the mid 1970s Viking
biology experiments did not find any organic compounds in
the soil. The soil was heated in the Viking biology experiments. Heated perchlorates
release their oxygen and burn up and organic material! So maybe the
release of carbon dioxide seen in the Viking experiments was actually from the
disintegration of trace organic material.
These findings show that the road to indentifying
extraterrestrial life is long and arduous, with potential dead ends and
misinterpretations. But the payoff of a positive detection is so staggering,
the long haul and lively debate among scientists is well worth it.
If there were any residents on Saturn’s giant moon Titan, their Xmas card would show a snowy ground of ammonia frost, beneath a pumpkin-orange sky, with a picturesque volcano blowing a sky-high fountain of water-ice crystals in the background.
Fanciful? Not really.
Scientists meeting this week at the American Geophysical Union conference reported that several years' worth of monitoring Titan by NASA’s Cassini orbiter offers evidence that the icy moon has volcanoes that spew out water instead of molten lava.
Cassini found that these volcanic-looking formations changed brightness between 2004 and 2006, suggesting a volcanic eruption. There is also evidence that ammonia frost is present at one of the two volcanic sites. The ammonia was seen only at times when the region was thought to be active. So, the ammonia was possibly ejected by the volcano, from a water ammonia slushy ocean inside the moon.
This bolsters the evidence from earlier stereoscopic images that show the absence of ancient impact craters in the suspected volcanic regions, and reveals the telltale topography of the cone-shaped volcanic summits with outflows. Infrared picture of moon show a suspected eruption-fueled haze hovering over surface formations that at least superficially resemble viscous flows.
Admittedly, an ice volcano is hard to imagine if you’ve ever seen Hawaii’s Kilauea volcano oozing out red-hot molten lava. But to an unimaginably exotic Titan inhabitant somehow acclimatized to a minus 300 degree Fahrenheit surface, the sight of liquid water spurting out of a mountain would look just as fearsome and devastating. “If Mount Vesuvius had been a cryovolcano, its lava would have frozen the residents of Pompeii," Cassini scientist Rosaly Lopes told reporters.
Instead of noxious sulfur dioxide fumes as found at Kilauea, a cryovolcano would spew out methane to replenish the methane in Titan’s nitrogen atmosphere, and also release ammonia. Titan's original atmospheric methane should have been exhausted long ago by photochemical reactions with sunlight, and scientists have been searching for a mechanism to replenish it. Volcanism is the logical choice.
The volcanoes tower over equatorial dune fields that are very much like the dunes of Africa's northern desert, although the sands are not silicates but hydrocarbons like methane and ethane.
What’s powering Titan’s volcanoes? Scientists first thought it was gravitational tidal heating by Saturn, just as Jupiter’s moon Io is kept hot enough by tidal pumping to power several active volcanoes continuously. But perhaps, just as plausibly, Titan's rocky core contains radioactive elements like uranium and radioactive potassium to heat an organic-rich liquid mantle of upwelling water-ammonia "lava."
What’s intriguing is that this makes Titan a virtual grocery store for finding the chemistry used by life: hydrogen and oxygen come from the water, carbon and hydrogen from the methane, nitrogen and hydrogen from the ammonia.
A study by the National Academy of Science in 2007 concluded that “Titan meets the absolute requirements for life.” Titan has a flow of energy from a warm interior to frigid surface, and it has abundant carbon-containing molecules in a fluid environment. Also Titan’s temperature is low enough to permit a wide range of complex molecules bonding together.
If life does not arise out of Titan's carbon chemistry even under these exotic conditions, then it may be more rare in the universe than we might imagine. Alternatively,Titan may be the archetype of a class of inhabitable cryo-moon orbiting the gas giant planets scattered throughout the galaxy.
In fact Titan, has earned the nickname “Earth II” among some of my planetary scientist colleagues. At first glance any comparison with Earth may seem awfully far fetched where surface temperatures of minus 300 degrees Fahrenheit are cold enough to turn water-ice rock hard.
But we simply should think of Titan as “Earth on ice” where atmospheric, aeolian, and geologic processes take place, but at frigid temperatures. An exotic cryo-chemistry replaces the rock, water and sand on Earth. But the processes themselves and the phenomena that result, such as sand dunes, river channels, lakes, rain clouds, and now volcanoes, are remarkably similar.
One of my favorite long forgotten video arcaded games of the 1980s was called Star Castle. It consisted of concentric counter rotating rings protecting an alien battle station. Your job was to use little fighters to blast away segments of the octagonal rings and blow up the battle station before its defender missiles got you.
So, I had a weird 80s flashback moment when viewing dramatic new pictures from one billion miles away sent back the NASA’s Saturn-barnstorming Cassini orbiter.
They revealed eerie, concentric rings, and even a hexagonal pattern of clouds and planet-swallowing cyclones swirling at Saturn’s poles. No, there aren't any little alien spaceships flitting around, but some of the cloud structures look so geometric you might convince yourself that they were the handiwork of an extraterrestrial intelligence.
If I had see such a feature in a space illustration I’d probably say to the artist: “Get real! Nothing on a planet can look that bizarre!”
These uncanny looking structures aside, at first glance Saturn’s poles look like they have a case of the measles.
Cassini’s infrared vision penetrated Saturn’s methane haze to reveal a speckled pattern of clouds located nearly 80 miles deep in the atmosphere. They look like dark storms only because they are silhouette against Saturn’s interior that glows in infrared light.
What’s not obvious in the wide field of view is the fact the dozens of Saturn-freckles are really vast convection cells of upwelling material dredged from deep inside the planet. Heat released from the condensing water in mega-thunderstorms at the base of the columns creates the billowing cloud tops. Unlike thunderstorms on Earth that are powered by sunlight, these storms suck up heat from Saturn's hot interior. One of cells at the south pole has so much energy it punched through to a higher altitude and created its own little vortex.
The new infrared false color view shows that Saturn's muted pastel beauty in visible light is only skin deep. Look beneath the soft haze and the planet is a roiling, turbulent, and seething cauldron of bubbling deep convection cells.
The upwelling storms power a hurricane-like vortex swirling around the poles at 300 miles per hour. At the south pole it forms a bull’s-eye pattern of concentric rings of walls of clouds. Nothing quite like this has ever been seen on the other gas giant planets.
Cassini also found a similar cyclone at Saturn’s even more bizarre north pole. Because Saturn is inclined on it axis much like the Earth, it has seasons during its 30-year orbit about the sun. This means the north pole is now in shadow. But this doesn’t stop Cassini infrared night vision.
The north pole has an arresting appearance because of an uncanny hexagonal cloud pattern photographed by Cassini earlier this year. Heaven help us if it were a pentagon instead, it might be interpreted by some factions as the handiwork of the devil.
The 15,000-mile diameter hexagon does not seem to move while the clouds whip around inside of it. Nor does the hexagon appear any bit disturbed by the turbulence.
NASA’s Voyager 1 and 2 spacecraft first spotted the hexagon in the early 1980’s. Cassini now shows a darker hexagon surrounds the brighter, previously recorded one.
This hexagon has sort of a mystical following on the Internet. It has been described by alien conspiracy theorist Richard Hoagland as a “hyper dimensional hexagon,” that is channeling energy from a parallel universe. (And according to Hoagland is also symptomatic of a solar system wide phenomena causing global warming!)
The simplest explanation is that it is a six-sided wave, of sorts, is going around the planet. But the uncanny straightness of the clouds walls makes it hard to believe that the structure is built and sustained by atmospheric hydrodynamics caused by jet streams or waves.
However, researchers at the Technical University of Denmark in Lyngby recreated the hexagon by simply spinning paint can sized buckets of water. The water formed a whirlpool that rose up the sides of the container until a hole formed in the middle. The dry center spot wasn't circular as might be expected. Instead, as the bucket spun-up the hole formed an ellipse, then morphed to a three-sided star, then into a square, a pentagon, and, at the highest speeds reached, a hexagon. (I wonder what it would take to make an octagon.)
Hydrodynamicists describe the hexagon as a "Rossby standing wave." This is caused by a circular fluid stream rotating clockwise, and a second nearby fluid stream rotating counter clockwise. The difference between the two streams will set up a resonance pattern.
Rossy vortices have been proposed as the cause of the partial hexagonal shape of a stellar super cluster in galaxy NGC6946, galaxy NGC 7421, galaxy NGC 7646a, and the shape of the interior vortex of Jupiter's Great Red Spot.
Even if the hexagon’s hydrodynamics are eventually fully understood, another mystery remains: how do you get these two different types of large-scale features on a planet that should be symmetrical at both poles?
More than likely it’s because the northern polar region has been in shadow for nearly 15 years, while the south pole has been in sunlight.
We may have new clues before 2010. By then sunlight will start hitting the northern hexagon. Astronomers will be able to look at it under sunlight illumination. They will presumably see a swirling vortex with hurricane-like high eye-walls and dark central clouds like the one now visible at the south pole.
But who knows? Saturn's unearthly atmosphere no doubt has more surprises for us.
In Arthur C. Clarke’s novel 2001: A Space Odyssey (which was written after the debut of the landmark 1968 motion picture) he describes alien visitors shattering a moon around Saturn 4 million years ago. It formed the gas giant planet’s ring system. This seemed to be the result of some construction activity as the extraterrestrials left behind the legendary black monolith “calling card” on the mysterious two-tone moon Iapetus.
I remembered this fanciful explanation for Saturn's rings when I saw reports from the Voyager 1 and Voyager 2 fly-bys of Saturn the early 1980s. Voyager found there are thousands of rings made of up billions of particles of ice and rock. The estimated sizes for the debris ranged from a grain of sugar to the size of a house.
The Voyager teams said that the rings are so bright they should be relatively young. Ring material should darken over time from in falling pitch-black meteoric dust. The rings Voyager photographed around Uranus and Neptune, by contrast, are black as charcoal and were called “old and decrepit,” by Voyager scientists.
Analysis of Voyager observations, as well as Hubble Space Telescope observations in the 1990s supported the theory that Saturn’s rings should be young. They might have formed at the time of the dinosaurs only 100 million years ago.
The problem with this theory is that it is anti-Copernican. It assumes we are living at a special time when the rings formed. In other words, to quote skater Nancy Kerrigan from 1994: “Why me, why now?” (Referring to a crippling attack by a jealous competitor.)
Back then I assumed the only way out of this dilemma was to have the rings form through a catastrophic moon collision around Saturn happening once every few hundred million years. This would periodically replenish the rings. But such collisions should be statistically unlikely. All the planetary bang-ups happened 4 billion years ago in the waning days of the solar system’s formation.
Now, NASA's Cassini spacecraft has shown that rings are continually being rototilled through bumping and grinding of icy debris. Moons are continually shattered into ring particles, which then gather together and re-form moons.
So, rather than orbiting smoothly around the planet, as was previously thought, the particles tend to clump together. The big surprise is that this means the rings could be three times more massive than computed from Voyager. This buys them time to hang around for billions of years.
If there were a parent body that shattered to initially form the ring debris 4 billion years ago, during the time of heavy meteorite bombardment in the solar system, it would have been roughly comparable in size to Dione, one on Saturn’s larger icy moons.
An alternative theory is that that the rings were born out of a circumplanetary disk of debris that could never coalesced to form moons because of the close gravitational tidal pull of Saturn.
Larry Esposito of the University of Colorado's Laboratory for Atmospheric and Space Physics presented his analysis at the meeting of the America Geophysical Union last year. Last Tuesday his results were presented at the European Planetary Science Congress in Muenster, Germany.
Esposito’s team discovered 13 objects in Saturn’s narrow, braided F ring ranging from a third the size of a football field to six miles across. Esposito says that because the objects are translucent they probably are temporary clumps of icy boulders that are continually sticking together and then coming unglued in an endless cycle.
This seesaw means that Saturn will keep rings well into the future, but they won't be exactly the same ring system we see today. This underscores the dynamics or ring systems seen around all the outer planets.
Saturn’s rings will eventually ablate away 5 billion years from now according to predictions by astrophysicists William Danchi, Bruno Lopez and Jean Scheider. They estimate that as the aging sun balloons into a red giant, a “habitable zone” warm enough to melt ice will sweep through a range of 200 million to 1 billion miles -- Saturn’s distance. So the rings are destined to melt away.
The Cassini findings imply that ring systems are long-lived around gas giant plants across the galaxy. The Hubble Space Telescope has look for rings around extrasolar gas giant planets seen in silhouette against their stars during a transit. They ring would have a unique signature in the way the planet blocks light from its star.
Not so surprisingly, Hubble hasn’t found rings. This is probably because the planets are so close to their stars the rings are dynamically unstable, or at least anemic because the ice volatiles evaporated away when the planet migrated in close to its star, perhaps leaving behind a tenuous dusty ring.
Nevertheless, the splendid beauty of Saturn-like worlds likely adorns innumerable planetary systems. And that is comfortably Copernican. In other words, there is nothing that unique about our own lord of the rings.
At first glance they look like invading spaceships with contrails, or brilliant runaway stars with sweeping comet-like tails.
NASA’s Cassini spacecraft has sent back striking photos of two small Saturn moons that are leaking dust into space. Caught in brilliant sunlight, the dust particles smear out to trace only part of the moons’ orbital paths. This sculpts incomplete “ring arcs” around Saturn.
This is the first time that isolated ring arcs have been seen around Saturn. Back in 1989 NASA’s Voyager 2 probe saw ring segments, looking like cut loops of spaghetti, encircling Neptune.
In 2005 Hubble Space Telescope retuned sharp pictures of dark ring arcs around Uranus.
The arcs dramatically illustrate the exotic and fluid ring dynamics around these gas giants.
The sources of Saturn’s ring arcs are a pair of mile-wide moons: Methone, discovered by Cassini in 2004, and Anthe, discovered in Cassini images in 2007. Both moons are located between the orbits of the much larger moons Mimas and Enceladus.
The two small moon are bombarded by meteoroids. The dust that’s kicked-up from the impacts escapes their gravity and goes into orbit around Saturn. The dust would smear into a full ring except for the gravitational tug of Mimas.
The extra gravitational pull is not much, but it always occurs at the same point in the ring particles' orbit as Mimas moves by. This is called a resonance orbit. The synchronization between the moons’ orbits is like pushing a child on a swing. If you given an additional push every time the swing is at the same point, you can boost the swing’s motion. The result is that Mimas gravitationally tugs on the small moons’ escaped dust and corrals the particles along an arc.
Imagine the view from the surface of one of these small moons. A brilliant streamer of shining dust would span horizon to horizon. It may be dense enough to eclipse the sun at the right viewing angle. This would cast an eerie long black stripe shadow across the surface terrain. Saturn and its majestic rings would span one quarter of the pitch-black sky.
The presence of ring arcs was first predicted earlier this year when Elias Roussos, of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany detected two peculiar breaks in the near-constant rain of high-energy electrons that bombard Cassini when near Saturn. The effect is similar to experiencing brief moments without rain falling on the windshield when driving under a bridge. These gaps in the flow of electrons showed that something over 1,000 miles wide was absorbing the charged particles. A ring arc of debris was the best solution.
Meteoroid abrasion also forms Jupiter's faint continuous rings at the orbits of the moons Amalthea, Thebe, Metis and Adrastea. In fact, rings complete rings of similar origin have also recently been detected in Cassini images along the orbits of the Saturnian moons Janus, Epimetheus and Pallene.
When you look at Saturn through a small telescope three main ring zones can be seen as solid and stately. Now thanks to Cassini we are seeing the “sausage making” process up close where things get messy under the relentless play of gravity. The ring arcs betray a wild and ever-changing side to Saturnian system.
In a piece of interplanetary barnstorming not seen since Star Wars’ Han Solo swooped through an asteroid belt, yesterday NASA’s Cassini orbiter skimmed just 20 miles above the frozen surface of Saturn’s icy moon Enceladus.
To make this even more exciting, the Winebago-sized explorer zoomed through 120-mile high water-ice geysers shooting out of the crust near the south pole.
A suite of instruments aboard the Battlestar Galactica class orbiter was trained intently on 80-mile long parallel fissures dubbed “tiger stripes.” (To me they look more like Godzilla claw scratches across the pristine white sphere.) Scanning the feature across the spectrum, from ultraviolet to infrared, Cassini may show if water or water vapor is near the moon’s surface.
Seeing inside one of the fissures will tell how deep they extend into the planet’s surface. The fissures are a comparatively balmy -292 degrees Fahrenheit compared to the expected temperature of -334 degrees Fahrenheit.
Enceladus' south pole is the equivalent of Yellowstone Park’s Old Faithful geyser. The tiger stripes vent vapor and fine ice water particles that resurface part of Enceladus like snow-making equipment at a ski resort.
Enceladus was unquestionably a strange-looking moon when NASA’s Voyager 2 spacecraft first photographed it in 1981. Parts of the surface appeared remarkably smooth and no older than 100 million years. Ancient craters had been wiped out by some geologic process, most likely cryo-volcanoes that spew out water instead of molten lava. This could mean the presence of a subsurface ocean to provide the volatiles.
But scientists were unable to explain how a moon no bigger than the state of Utah could get hot enough to melt ice. It’s probably too small to have enough radioactive material to heat its core.
Cassini reopened the mystery 24 years later when it photographed the geyser-like jets on Enceladus. These are presumably propelled by subsurface liquids. The geysers create a halo of ice and gas around Enceladus and feed material into Saturn’s E-ring.
The most likely form of heating could come from gravitational tidal forces from Saturn and other satellites tugging and pulling on Enceladus. This process keeps Jupiter’s tiny moon Io volcanically active.
However, Enceladus' orbit would have to be three times more elliptical to undergo the warming stresses to keep an ocean liquid, say researchers. It’s possible the moon's eccentricity and tidal heating may have fluctuated up and down many times over tens of million of years.
If Enceladus has an ocean, it may stay liquid due to antifreeze in the form of salts and ammonia. The ocean itself would generate tidal heating by sloshing back and forth like the ocean tides do on Earth.
The idea of a liquid medium for life on this worlds is especially exciting because carbon dioxide and organic molecules like methane, ethane and ethylene are bubbling up through the vents. So a moon a billion miles from the Sun, far beyond the solar system’s habitable zone, could be a stew for extremeophiles.
However, Susan Kieffer and colleagues from the University of Illinois poured cold water on this idea by offering an alterative model to a subsurface ocean. They say the plumes originate in the dissociation of certain stiff compounds of ice, called clathrates. These are an ice phase of nitrogen and methane that can be much colder than liquid water. Kieffer says that the plumes of material are erupting from these clathrates, spewing nitrogen, methane, carbon dioxide and chunks of water ice into space. This would do away with the need for a subsurface ocean.
Cassini's latest observation may shed light on what is really happening on the unexpectedly active and strange captive of Saturn. Stay tuned for more excitement and adventure as the latest flyby results are reported by the Cassini team.
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