New data suggests that the icy crust of Titan is twice as thick as previously estimated.

New data suggests that the icy crust of Titan is twice as thick as previously estimated.

“The picture of Titan that we get has an icy, rocky core with a radius of a little over 2,000 kilometers, an ocean somewhere in the range of 225 to 300 kilometers thick and an ice layer that is 200 kilometers thick,” [said Howard Zebker of Stanford University]. Previous models of Titan’s structure estimated the icy crust to be approximately 100 kilometers thick.

This means that the methane lakes and rivers of Titan are flowing across a bedrock of ice, which at the cold temperatures there would be as solid as rock is here on Earth.

Data of the tidal fluxes on Titan by the Cassini spacecraft now suggest that there is a liquid ocean below Titan’s icy crust.

Data of the tidal fluxes on Titan by the Cassini spacecraft now suggest that there is a liquid ocean below Titan’s icy crust.

The team’s analyses suggest that the surface of the moon can rise and fall by up to 10 metres during each orbit, says Iess. That degree of warpage suggests that Titan’s interior is relatively deformable, the team reports today in Science1. Several models of the moon’s internal structure suggest such flexibility — including a model in which the moon is solid but soft and squishy throughout. But the researchers contend that the most likely model of Titan is one in which an icy shell dozens of kilometres thick floats atop a global ocean. The team’s findings, together with the results of previous studies, hint that Titan’s ocean may lie no more than 100 km below the moon’s surface.

Engineers have gone to a back up radio system on Cassini after a primary unit did not respond as expected in late December.

Engineers have gone to a back up radio system on Cassini after a primary unit did not respond as expected in late December.

The cause is still under investigation, but age may be a factor. The spacecraft launched in 1997 and has orbited Saturn since 2004. Cassini completed its prime mission in 2008 and has had two additional mission extensions. This is the first time its ultra-stable oscillator has had an issue.

Sponge in space

Hyperion

On August 25 Cassini did a close fly-by of the small Saturn moon Hyperion, getting as close as 15,500 miles. The mission has just released images from that fly-by.

Looks like a sponge, doesn’t it? This moon is small, only 168 miles across, which makes it about half the size of the asteroid Vesta that Dawn is presently orbiting. Why it is so peppered with craters is of course the big science question. I would guess this has something to do with the environment around Saturn, with its rings and the innumerable particles that come from it. Yet, other moons of Saturn are not as crater-filled, so there is obviously more to this than meets the eye.

This fly-by was the second closest of Hyperion that Cassini has done, the first passing over the the moon’s surface by only 310 miles. Because the irregularly-shaped moon’s rotation is more like a chaotic tumble, scientists could not predict what part of the surface they would see. To their luck the new images captured new territory.

Another fly-by is scheduled in only three weeks, on September 16, 2011. This time, however, the spacecraft won’t get as close, passing at a distance of about 36,000 miles.

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.

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