Tag Archives: Enceladus

New model for Enceladus’s subsurface ocean

A new model proposes that the subsurface liquid water ocean of Saturn’s moon Enceladus is possible only 3 miles below the surface near its south pole.

In order to reconcile the different constraints [created by the known data], the researchers propose a new model in which the top two hundred meters of the ice shell acts like an elastic shell. According to this study, Enceladus is made up successively of a rocky core with a radius of 185 km, and an internal ocean approximately 45 km deep, isolated from the surface by an ice shell with a mean thickness of around 20 km, except at the south pole where it is thought to be less than 5 km thick. In this model, the ocean beneath the ice makes up 40% of the total volume of the moon, while its salt content is estimated to be similar to that of Earth’s oceans.

Need I mention that this is only a computer model, and should therefore be considered with great skepticism?

Posted from warm and dry Tucson, Arizona, where I am home at last!

The jets of Enceladus

Enceladus's jets

Cool image time! The image above, taken in June by Cassini, shows the night side of Saturn’s moon Enceladus, framed by Saturn’s rings, and faintly showing the jets of water coming from its south pole. To show it here I have cropped it and reduced it somewhat, as well as brightened the jets to make them more visible.

The release notes how the image compares the frozen water of Saturn’s rings and the liquid activity of Enceladus’s jets. I note how the image is simply beautiful. Be sure to click on the link to see the full resolution image.

Enceladus rises over Dione

Enceladus rising behind Dione

Cool image time! The image on the right was taken by Cassini in September 2015, and shows two Saturn moons, bright Enceladus partly blocked by darker and nearer Dione.

Although Dione (near) and Enceladus (far) are composed of nearly the same materials, Enceladus has a considerably higher reflectivity than Dione. As a result, it appears brighter against the dark night sky.

The surface of Enceladus (313 miles or 504 kilometers across) endures a constant rain of ice grains from its south polar jets. As a result, its surface is more like fresh, bright, snow than Dione’s (698 miles or 1123 kilometers across) older, weathered surface. As clean, fresh surfaces are left exposed in space, they slowly gather dust and radiation damage and darken in a process known as “space weathering.”

The image doesn’t contain any earth-shattering discoveries. It is simply beautiful. And in these dark times, seeing beauty is sometimes the most important thing one can do.

An Enceladus close look

Enceladus at 77 miles

Cool image time! The image on the right is the first processed close-up image released from Cassini’s fly-by of Saturn’s moon Enceladus on Wednesday. The resolution is about 50 feet per pixel, taken from about 77 miles away. This surface, in the general area where Enceladus vents lie, reminds me of a thick field of snow that has begun to melt away.

Since the fly-by got within 30 miles, even higher resolution images should follow.

Enceladus flyby images begin arriving

Enceladus

Cool image time! The first images from Cassini’s close flyby of Saturn’s moon Enceladus on Wednesday have started to arrive.

None have yet been processed, though the press release above provided a distant view of the moon’s plumes as the spacecraft approached. The image on the right, showing the moon itself, is one of the flyby I pulled off from the raw image website. Expect some interesting views to appear there throughout the day, with a more detailed press release tomorrow.

Fractures on Enceladus’s north pole

Enceladus's North Pole

The Cassini science team has released the first image from Wednesday’s flyby of the Saturn moon Enceladus.

Scientists expected the north polar region of Enceladus to be heavily cratered, based on low-resolution images from the Voyager mission, but the new high-resolution Cassini images show a landscape of stark contrasts. “The northern regions are crisscrossed by a spidery network of gossamer-thin cracks that slice through the craters,” said Paul Helfenstein, a member of the Cassini imaging team at Cornell University, Ithaca, New York. “These thin cracks are ubiquitous on Enceladus, and now we see that they extend across the northern terrains as well.”

To see more you can browse the raw images here.

The next flyby later this month will be especially interesting as they will dip to within 30 miles of the surface.

Cassini’s last flybys of Enceladus

As Cassini approaches the end of its decade-long mission at Saturn it will begin its last series of flybys of the moon Enceladus starting October 14.

Images will arrive a day or two afterward. The last two flybys will take place in late October and then in December, with the second October flyby getting closest, only 30 miles from the surface.

Beginning next year they will shift the spacecraft’s orbit so that it can get a better look at Saturn’s poles during its last two years. In that orbit flybys of the moons cannot be done.

Giant global ocean inside Saturn’s moon Enceladus

Using data from seven years of flybys by Cassini of Enceladus scientists now think they have confirmed the existence of a global ocean of liquid water beneath the moon’s icy crust.

Cassini scientists analyzed more than seven years’ worth of images of Enceladus taken by the spacecraft, which has been orbiting Saturn since mid-2004. They carefully mapped the positions of features on Enceladus — mostly craters — across hundreds of images, in order to measure changes in the moon’s rotation with extreme precision. As a result, they found Enceladus has a tiny, but measurable wobble as it orbits Saturn. Because the icy moon is not perfectly spherical — and because it goes slightly faster and slower during different portions of its orbit around Saturn — the giant planet subtly rocks Enceladus back and forth as it rotates.

The team plugged their measurement of the wobble, called a libration, into different models for how Enceladus might be arranged on the inside, including ones in which the moon was frozen from surface to core. “If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be,” said Matthew Tiscareno, a Cassini participating scientist at the SETI Institute, Mountain View, California, and a co-author of the paper. “This proves that there must be a global layer of liquid separating the surface from the core,” he said.

Previous data had suggested a lens-shaped ocean under the south pole. This new data suggests the ocean in global.

As always, the possibility of liquid water suggests the possibility of life. None has been found, but with water and energy it is certainly possible.

Tiny grains from the interior ocean of Enceladus

Using Cassini scientists have detected tiny grains of rock orbiting Saturn that they think were formed on the floor of the interior ocean of Enceladus and then spewed out its vents into space.

They believe that these silicon-rich grains originate on the seafloor of Enceladus, where hydrothermal processes are at work. On the seafloor, hot water at a temperature of at least 90 degrees Celsius dissolves minerals from the moon’s rocky interior. The origin of this energy is not well understood, but likely includes a combination of tidal heating as Enceladus orbits Saturn, radioactive decay in the core and chemical reactions.

As the hot water travels upward, it comes into contact with cooler water, causing the minerals to condense out and form nano-grains of ‘silica’ floating in the water. To avoid growing too large, these silica grains must spend a few months to several years at most rising from the seafloor to the surface of the ocean, before being incorporated into larger ice grains in the vents that connect the ocean to the surface of Enceladus. After being ejected into space via the moon’s geysers, the ice grains erode, liberating the tiny rocky inclusions subsequently detected by Cassini.

Additional data suggest that the interior of Enceladus is very porous, which means that interior ocean might not be one large bubble but a complex liquid-filled cave.

Planet of geysers

Using Cassini data assembled over the past seven years, scientists have now identified 101 distinct geysers erupting on the surface of the Saturn’s moon Enceladus.

Over a period of almost seven years, Cassini’s cameras surveyed the south polar terrain of the small moon, a unique geological basin renowned for its four prominent “tiger stripe” fractures and the geysers of tiny icy particles and water vapor first sighted there nearly 10 years ago. The result of the survey is a map of 101 geysers, each erupting from one of the tiger stripe fractures, and the discovery that individual geysers are coincident with small hot spots. These relationships pointed the way to the geysers’ origin.

The really important discovery here however is this:
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Is it snowing microbes on Enceladus?

Is it snowing microbes on Enceladus?

“More than 90 jets of all sizes near Enceladus’s south pole are spraying water vapor, icy particles, and organic compounds all over the place,” says Carolyn Porco, an award-winning planetary scientist and leader of the Imaging Science team for NASA’s Cassini spacecraft. “Cassini has flown several times now through this spray and has tasted it. And we have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth’s oceans.”

Enceladus rains water onto Saturn

The Herschel space telescope has discovered that the water expelled from the tiger stripes on Enceladus eventually rains down on Saturn.

Enceladus expels around 250 kg of water vapour every second, through a collection of jets from the south polar region known as the Tiger Stripes because of their distinctive surface markings. These crucial observations reveal that the water creates a doughnut-shaped torus of vapour surrounding the ringed planet. The total width of the torus is more than 10 times the radius of Saturn, yet it is only about one Saturn radius thick. Enceladus orbits the planet at a distance of about four Saturn radii, replenishing the torus with its jets of water.

Cassini directly samples the plumes from Enceladus and finds an ocean-like Spray

Cassini has directly sampled the plumes from Enceladus and discovered a salty ocean-like spray.

The new paper analyzes three Enceladus flybys in 2008 and 2009 with the same instrument, focusing on the composition of freshly ejected plume grains. The icy particles hit the detector target at speeds between 15,000 and 39,000 mph (23,000 and 63,000 kilometers per hour), vaporizing instantly. Electrical fields inside the cosmic dust analyzer separated the various constituents of the impact cloud.

The data suggest a layer of water between the moon’s rocky core and its icy mantle, possibly as deep as about 50 miles (80 kilometers) beneath the surface. As this water washes against the rocks, it dissolves salt compounds and rises through fractures in the overlying ice to form reserves nearer the surface. If the outermost layer cracks open, the decrease in pressure from these reserves to space causes a plume to shoot out. Roughly 400 pounds (200 kilograms) of water vapor is lost every second in the plumes, with smaller amounts being lost as ice grains. The team calculates the water reserves must have large evaporating surfaces, or they would freeze easily and stop the plumes.