CAPTION: Giant boulders appear as white bumps in this close-up shot of Enceladus. They do not fill in the cracks on the icy moon's surface, suggesting the boulders formed before the fractures (Image: NASA/JPL/Space Science Institute)
Posted on 07/19/2005 11:15:30 AM PDT by LibWhacker
The Cassini spacecraft has coasted to its closest encounter yet - skimming just 175 kilometres above Saturn's icy moon Enceladus. But astronomers are at a loss to explain its observations.
On 14 July, Cassini swooped in for an unprecedented close-up view of the wrinkled moon. Its Imaging Science Subsystem (ISS) camera has since returned pictures of a boulder-strewn landscape that is currently beyond explanation. The "boulders" appear to range between 10 and 20 metres in diameter in the highest-resolution images, which can resolve features just 4 m across.
“That’s a surface texture I have never seen anywhere else in the solar system,” says David Rothery, a planetary geologist at the Open University in Milton Keynes, UK.
Cracks crisscross Enceladus's surface - possibly as a result of the moon being repeatedly squeezed and stretched by the gravity of Saturn and other moons nearby. But Rothery points out the boulders avoid - rather than fill - the cracks. This might indicate that the fracturing took place after the boulders had already formed.
Alien landscape
John Spencer, a Cassini team member at the Southwest Research Institute in Boulder, Colorado, US, agrees that the images are puzzling. “You would expect to see small craters or a smooth, snow-covered landscape at this resolution," he told New Scientist. "This is just strange. In fact, I have a really hard time understanding what I’m seeing.”
NASA scientists have been locked in discussions since 15 July and are expected to pass judgment on what they think this peculiar surface might be later on Tuesday.
But Elizabeth Turtle, a Cassini imaging team member at the University of Arizona in Tucson, US, warns there will be no quick answers. “Trying to figure out what is going on is going to take a lot longer than a weekend of swapped emails,” she says.
Heat source
These images - like those from previous flybys - reveal a surface clawed with fractures and swollen with ridges. It could point to a substantial heat source within the moon, driving the internal convection of ice. And this raises the possibility that Enceladus could possess a sub-surface ocean similar to that on Jupiter's moon Europa.
That could be a problem, according to Spencer. Superficially, the two worlds bear a passing resemblance, but Enceladus is six times smaller than Europa. “Enceladus seems too small to have enough internal heat to create a sub-surface ocean," he says. "But, since we don’t understand the surface, we might not understand the interior either,” he says. Turtle, however, is sceptical of the ocean hypothesis and says "we see no evidence of liquid flows on the surface”.
Key information in this debate may come from Cassini’s Dual Technique Magnetometer. It was fluctuations in Europa’s magnetic field that finally convinced scientists that it harboured a subsurface ocean. Perhaps the same will be true of Enceladus. At present, the data is being analysed by scientists at Imperial College in London, UK.
Regardless of the outcome, NASA has already decided that Enceladus is worth an even closer look. They have scheduled another grazing flyby of the moon in 2008, when Cassini will skim even closer than ever - to within 100 km of the boulder-strewn surface.
CAPTION: Giant boulders appear as white bumps in this close-up shot of Enceladus. They do not fill in the cracks on the icy moon's surface, suggesting the boulders formed before the fractures (Image: NASA/JPL/Space Science Institute)
Cold enchiladas? I'll pass.
They way I see it, when a crack opens up, it swallows whatever is on the downhill slope and then fills in with a liquid that freezes on the surface and essentially creates a fresh cover.
... but I did stay at a Holiday Inn Suites.
I'm holding off until I hear what George Noory has to say about this.
Not possible. Perhaps 1/6 the size of Europa?
LOL
Was watching Natalie's mom on tv yesterday talking about Joran van der Sloot and she kept calling him 'Urine.' Urine did this. Urine did that. Urine on the beach, lol.
However, spending a lot more taxpayer dollars will help us all get the answer which has surely puzzled billions of people worldwide, namely, where do the icy boulders on Encelaus come from. I know it's kept me up many nights.
What, the highest libdo you say?
Where do people learn to write these days? This: "when Cassini will skim even closer than ever" is a poorly constructed phrase. It would suffice to say that "Cassini will skim even closer", or "Cassini will skim closer than ever," but to use both "even" and "ever" is redundant.
Huh. And here I thought the moon took the honors. Goes to show you learn something new every day on FR.
Makes sense in a way: 'n times larger' means you multiply the quantity in question by n -- 'n times smaller' means you multiply the quantity in question by one over n. 'Ya don't see it much in the math journals though!
Cold enchiladas with boulders, yet!.....
Covered in "water ice"?
What flavor?
Enceladus has an albedo of .99 - it don't get any higher than that!!
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