Carbonated oceans, moons torn apart, ring tsunamis—there’s a flurry of cool news about Saturn coming out of the American Astronomical Society’s Division for Planetary Science meeting in Pasadena, California.
The fizzy ocean of Enceladus
Saturn’s moon Enceladus is one of the prime candidates for some kind of life elsewhere in the solar system, thanks the the possibility that a large subsurface ocean feeds the plumes of ice and vapor that the Cassini spacecraft has spied blasting forth from the moon. At the AAS meeting in California, Cassini scientists Dennis Matson proposed something new about this extraterrestrial ocean: It could be carbonated.
Noncarbonated seawater circulating from the moon’s solid core to the surface would stall rather than seep though cracks in the ice because seawater is denser than the icy carapace. If the seawater were fizzy, however, gas bubbles would form in the liquid, reducing the ocean’s density. Once the seawater became less dense than the ice, the water could rise to within 10 to 15 meters of the frigid surface. That’s close enough to fill chambers in the icy crust with water that feeds the south polar plumes. [Science News]
Auroras on Saturn form like those on Earth, when charged particles in the solar wind stream down the planet’s magnetic field towards its poles, where they excite gas in the upper atmosphere to glow. Some auroras on the ringed planet are also triggered when some of its moons, which are electrically conducting, move through the charged gas surrounding Saturn. [New Scientist]
They’re new, they’re small, and they didn’t make sense.
That’s what could be said for five of the littlest members of Saturn’s expansive satellite family. The largest of this group, Janus, measures barely more than 100 miles in diameter, but it’s the age of these little moons that’s the odd bit. Their clean, crater-free surfaces help reveal that they’re only 10 million years old, meaning they didn’t form the way the planet’s other moons did—from the accretion disk that formed mighty Saturn itself billions of years ago. This week in Nature, astronomers published evidence to support an explanation for that oddity: Those moons formed from Saturn’s rings.
Sailing past Saturn’s outer rings, it found lumps of ice up to 100 metres across, ten times bigger than the rings’ other icy particles. For some researchers, the discovery called to mind another intriguing fact: that the moons and the rings share a composition of the purest ice in the Solar System. “When you put all this together, you had the strange feeling that something is going on in the rings’ outer edge,” says Sébastien Charnoz at Paris Diderot University, who was involved in the latest research [Nature].
If there were life on the Saturnian moon of Titan, the thinking goes, it would have to inhabit pools of methane or ethane at a cool -300 degrees Fahrenheit, and without the aid of water. While scientists don’t know just what that life would look like, they can predict what effects such tiny microbes would have on Titan’s atmosphere. That’s why researchers from the Cassini mission are excited now: They’ve found signatures that match those expectations. It’s far from proof of life on Titan, but it leaves the door wide open to the possibility.
In 2005, NASA’s Chris McKay put forth a possible scenario for life there: Critters could breathe the hydrogen gas that’s abundant on Titan, and consume a hydrocarbon called acetylene for energy. The first of two studies out recently, published in the journal Icarus, found that something—maybe life, but maybe something else—is using up the hydrogen that descends from Titan’s atmosphere to its surface:
“It’s as if you have a hose and you’re squirting hydrogen onto the ground, but it’s disappearing,” says Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored a paper published in the journal Icarus [Popular Science].
Erring on the side of caution, the scientists suggest that life is but one explanation for this chemical oddity. Perhaps some unknown mineral on Titan acts as a catalyst to speed up the reaction of hydrogen and carbon to form methane, and that’s what accounts for the vanishing hydrogen. (Normally, the two wouldn’t combine fast enough under the cold conditions on Titan to account for the anomaly.) That would be pretty cool, though not as much of a jolt as Titanic life.
When we last covered NASA’s Stardust mission a couple weeks ago, we noted that it was one of those missions that just keeps popping up as new findings from its data makes the news. But Stardust might by outdone by another: Cassini, which continues to reveal new surprises about Saturn and its moons—not to mention sending back beautiful images like this new batch. Today in the journal Science, Cassini researchers review six years of Saturn science (here and here) by the hardy spacecraft.
The first review tackles the planet’s atmosphere and magnetosphere. Before Cassini, scientists thought that the magnetosphere, the shield from the solar wind that forms around a planet, contained nitrogen ions that had come from Saturn’s largest moon, Titan. Cassini showed that wasn’t so, and that wasn’t the only surprise about the magnetosphere: The spacecraft’s observations showed that it is dominated by water, part of which comes from water vapor plumes that shoot out of geysers on the surface of Saturn’s moon Enceladus. “The big news is that Saturn’s space environment is swimming in water,” said Tamas Gombosi, a Cassini scientist [Space.com].
Water, water everywhere. Another pass of Saturn’s moon Enceladus, made by the Cassini spacecraft last November, shows at least 30 geysers blasting water from the moon’s south pole. That’s 20 more than were previously known at that location. In addition, the most detailed infrared map of one of the south pole’s fissures, where jets emanate, indicates that the surface temperature there might be as high as 200 kelvins (-73º Celsius), or about 20 kelvins warmer than previously estimated [Discovery News]. Cassini drew to within about 1,000 miles of Enceladus to measure this geological feature, which is a fracture–one of the moon’s so-called “tiger stripes”–about a quarter-mile deep officially called Baghdad Sulcus.
While 200 kelvins is still a frigid temperature for we humans, research team member John Spencer said it could make a big difference on Enceladus. “The huge amount of heat pouring out of the tiger stripe fractures may be enough to melt the ice underground,” Spencer said. ”Results like this make Enceladus one of the most exciting places we’ve found in the solar system” [Wired.com].
Bad Astronomy: Enceladus Is Erupting!
80beats: Cassini Probe Finds “Ingredients For Life” on Saturn’s Moon Enceladus
80beats: Antifreeze Might Allow For Oceans—And Life—On Enceladus
80beats: Does Enceladus, Saturn’s Geyser-Spouting Moon, Have Liquid Oceans?
80beats: New Evidence of Hospitable Conditions for Life on Saturn’s Moons
80beats: Geysers From Saturn’s Moon May Indicate Liquid Lakes, and a Chance for Life
80beats: Cassini Spacecraft Snaps Pictures of Saturn’s Geyser-Spouting Moon
Five years ago, the Cassini spacecraft first detected plumes of water ice emanating from Saturn’s moon Enceladus, making the moon one of the best hopes for finding life somewhere else in the solar system. Astronomers have argued over whether or not those jets come from a subsurface ocean of liquid water, but new findings by Cassini provide evidence that water could indeed be sloshing around beneath the frozen surface of this small moon.
During a 2008 pass through the plumes, the spacecraft found negatively charged water molecules. Back home this short-lived type of ion is produced where water is moving, such as in waterfalls or crashing ocean waves [Scientific American]. Researcher Andrew Coates led the study, which is coming out in the journal Icarus.
With its thick atmosphere, chemical makeup, and an atmospheric pressure not too far from Earth’s, Titan is one of the most likely candidates for finding life elsewhere in our solar system. But at a temperature close to -300 degrees Fahrenheit, the surface of this Saturnian moon in anything but what we humans would call hospitable. Since this frigid place is far too cold for liquid water, any life there would need an alternative survival method. A new study published in Astrophysical Journal Letters suggests that the simple hydrocarbon acetylene, proposed as a possible energy source for life on Titan, could be much more abundant than scientists previously thought.
Titan has previously been shown to be dotted with lakes of liquid hydrocarbons, primarily methane and ethane. An estimate made in 1989 suggested bodies of liquid hydrocarbons on Titan would contain a few parts in 10,000 of acetylene. But an updated estimate based on data from the Cassini-Huygens mission to Saturn now suggests the lakes contain much more food for any hungry alien life-forms that might be present [New Scientist]. Lead researcher Daniel Cordier says the acetylene abundance could be as high as one part in 100, or 1 percent, of the surface lakes on Titan.
What lies beneath the icy crust of Enceladus? Ever since the NASA space probe Cassini snapped pictures of the Saturnian moon expelling enormous jets of icy vapor from fissures near its south pole in 2005, planetary scientists have debated whether the evidence points to liquid oceans beneath the moon’s surface. Now, a new chemical analysis of the plume bolsters the oceanic theory, thanks to the detection of a mundane chemical: ammonia. Says study coauthor Jonathan Lunine: “This is the first time Cassini has actually been able to ’smell’ ammonia…. And because ammonia is an antifreeze, it probably ensures that there is liquid water in the interior of Enceladus.” And where there’s water, there could be life [Wired.com].
Last month, another team of researchers also argued for the presence of an ocean when they published their discovery of sodium salts in Saturn’s outer-most ring which is thought to originate from Enceladus’ plume material. “The two studies are complimentary and now, for the first time, we are getting an idea of the full picture of what’s happening on Enceladus,” [Chemistry World], says Frank Postberg, lead author of that earlier study. However, Postberg’s study was contested by another paper that found no traces of sodium vapor around Enceladus, leaving the debate unresolved. Sodium is thought to be an indicator of liquid water because it suggests that salt leached from rocks into the water.
Saturn’s moon Enceladus got humanity’s attention in 2005 when surprised astronomers detected jets of ice and gas spraying out from the moon’s icy surface, and since then researchers have eagerly investigated the possibility that the jets might emanate from liquid oceans beneath the frozen crust. A moon with liquid water would be of great interest, because it would be more likely to host extraterrestrial microbes. Now, two new studies with somewhat contradictory results have deepened the mystery of what lies beneath Enceladus’s shell of ice.
Both groups of researchers were looking for sodium near Enceladus; one found it, the other didn’t. Sodium is interesting because it indicates that deep under the ice, liquid water has been in contact with rocks, which leach salts [ScienceNOW Daily News]. The dissolved sodium, along with water, would be shot into space in the geysers, and some of the sodium would be trapped in ice crystals as they formed. The first research group found sodium traces in Saturn’s E ring, a wide band of ice particles that is believed to be replenished by Enceladus’s jets. “Those salty grains provide our current best smoking (or steaming) gun pointing to present-day liquid water near the surface of Enceladus” [Wired.com], wrote space scientist John Spencer in an essay accompanying the findings.