Category Archives: moons

cassini mission, enceladus, planetary science, planets

Going South for the Summer

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Cassini at Enceladus: More!  More!

These are the infamous tiger stripes in the region on Enceladus where Cassini scientists spotted material coming out of vents.  It’s a false-color mosaic–meaning that several sets of images from the Imaging Subsystem were pieced together and colored to highlight specific units of the surface that scientists want to study. Here’s what the Cassini mission press release has to say about this image:

Areas that are greenish in appearance are believed to represent deposits of coarser grained ice and solid boulders that are too small to be seen at this scale, but which are visible in the higher resolution views, while whitish deposits represent finer grained ice. The mosaic shows that coarse-grained and solid ice are concentrated along valley floors and walls, as well as along the upraised flanks of the “tiger stripe” fractures, which may be covered with plume fallout that landed not far from the sources. Elsewhere on Enceladus, this coarse water ice is concentrated within outcrops along cliff faces and at the top of ridges. The sinuous boundary of scarps and ridges that encircles the south polar terrain at about 55 degrees south latitude is conspicuous. Much of the coarse-grained or solid ice along this boundary may be blocky rubble that has crumbled off of cliff faces as a result of ongoing seismic activity.

Wouldn’t it be fun to hike this area? Perhaps in the future, planetary geologists will bring their equipment here to sample the surface, measure its properties, and give all of us here on Earth the ultimate close-up pictures of this fascinating moon.

Just to give you an idea what Voyager 2 saw, here’s the image we all marvelled over 27 years ago this month. Even then, we were all fascinated with the juxtaposed terrains and mysterious cracks on this icy surface.  What a difference nearly three decades makes!

I’ve written before about the scene at Jet Propulsion Laboratory in Pasadena that night, when Enceladus showed us her stuff. It was a noisy, wonderful experience, made even  more exciting by the fact that when this picture came down from the Deep Space Network and scanned across the screen, it was during a live broadcast of Nightline. A lot of science writers and planetary scientists were standing around watching, and thus we were all together in one big happy family jabbering to each other about what we were seeing on the screens. We made so much noise when we saw the pics that the floor directors for Nightline had to shush us several times, pretty much to no avail!  Hey… we were watching planetary science history unfold before our eyes.  With all due respect to Ted Koppel, Enceladus was far more fetching and mysterious, and we weren’t going to let the chance go by to do instant science interpretation on that amazing image!

cassini mission, enceladus, planetary science, solar system exploration

Venting on Enceladus

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Cassini’s Cameras Hit the Target

Imagine flying all the way out to Saturn’s moon Enceladus to take images of a geyser vent the size of a small mountain from a distance of about 4,700 kilometers (about 2,900 miles) while whizzing past at a speed of 64,000 kilometers (40,000 miles) per hour. That’s exactly what the Cassini-Huygens mission did last week. In managing this feat, Cassini’s cameras pinpointed the origins of icy jets shooting material out from beneath the surface of this geologically active moon. The image at left shows the target areas and where Cassini spotted those vents.

These geyser-like spouts are in a region of “tiger stripe” terrain, named for the way the surface looks in earlier images of Enceladus. You can see fractures that are about 300 meters (980 feet) deep. The flanks of some of those fractures seem to have deposits of fine material that likely put there as plumes of vapor erupt through the vents. Blocks of ice tens of meters in size and larger (the size of small houses) surround the fractures.

Planetary scientists are really excited about this find because the mission is at last answering a lot of questions about Enceladus and its intriguing surface. “This is the mother lode for us,” said Carolyn Porco, Cassini imaging team leader at the Space Science Institute, Boulder, Colo. “A place that may ultimately reveal just exactly what kind of environment — habitable or not — we have within this tortured little moon.”

Enceladus has been a puzzle ever since the first Voyager 2 images showed its cracked, strangely repaved surface during a 1981 flyby. That evidence alone told scientists that something was going on with this little ice-covered moon, but they really needed high-resolution images. Voyager 2 was the reconnaissance mission to Cassini’s “in depth” followup.

So, how is Enceladus doing it?  What’s going on with those vents to cause what we see? It’s all in how material gets from relative warm areas deep inside Enceladus to the frigid surface. Imaging scientists suggest that once warm vapor rises from underground to the cold surface through narrow channels, the icy particles may condense and seal off an active vent. Because the material underneath is warmer and under some amount of pressure, it has to erupt somewhere, so eventually new jets probably appear elsewhere along the same fracture in fairly short order.

There’s more to come from the Cassini mission folks. To follow the action, check out new images at: http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and http://ciclops.org.  Check it out!