Oct 8, 2009 03:40 PM in Space | 5 comments
What caused Saturn to lurch? Second dispatch from the annual planets meeting
FAJARDO, Puerto Rico—I first heard about Matt Hedman's talk while going out to dinner on Tuesday night. Best talk of the meeting, I was told. Everywhere I went yesterday, I kept hearing about this guy Matt Hedman. A former professor of mine chided me for missing his presentation. The problem with the Division for Planetary Sciences meeting is that you have to make hard choices about which of many parallel sessions to go to, and clearly I'd made the wrong choice on Tuesday afternoon. Fortunately, I caught up with Hedman today and learned what is causing all the fuss.
Hedman, a Cornell University researcher, and his team have discovered a very curious feature in the rings of Saturn. Although it has gotten much less attention than Saturn's newly discovered ring, it may well be more significant. In mid-August, Saturn passed through its equinox and sunlight shone directly along the rings, so that even the most subtle vertical structure cast long shadows. Images from the Cassini spacecraft revealed that the planet's C ring has a gentle corrugation that extends across tens of thousands of kilometers. (Saturn has seven main rings, named A to G in order of discovery.) The ripples are barely 100 meters high and recur with a wavelength varying from 30 kilometers toward the planet to 80 kilometers farther out. The pattern appears to be an extension of a corrugation that scientists first noticed in Saturn's D ring back in 2005. What's more, the pattern seems to be evolving with time, its wavelength steadily diminishing. Extrapolating back in time, it must have been set in motion 25 years ago.
It looks like the ring—the whole ring—was abruptly yanked out of Saturn's equatorial plane. Pulled out of the plane, ring particles began to bob up and down, creating the corrugation; the giant planet's oblong shape tugged on the pattern, causing it to evolve. But what could possibly do that to a ring? A passing moon could scarcely cause such a vast disruption, Hedman says. Instead, he suggests that it wasn't the ring that shifted, but Saturn's equatorial plane. A tilt of a thousandth of a degree would suffice. "It's a little shift, but it affected the structure of the rings in a pretty profound way," Hedman says.
In other words, the entire planet Saturn suddenly lurched in the mid-1980s. A change in the planet's spin axis is out of the question. Saturn is, in effect, a gyroscope with a radius of 60,000 kilometers and the mass of 95 Earths. It isn't going to tilt over with anything short of an apocalyptic event. What must have happened instead is that mass shifted within the planet, reorienting the effective gravitational equator. But how? "It's not obvious how to shift Saturn's internal gravitational distribution fast enough to do this," Hedman says. Saturn modelers have clearly got their work cut out for them.
Previously: From carbon planets to the lakes of Titan: Dispatch from the annual planets meeting
Corrugations in Saturn's C and D rings, as seen by the Cassini spacecraft, courtesy of NASA/JPL/Space Science Institute
You Might Also Like
Discuss This Article
Subscription Center
Most Popular Blog Posts
9,000-year-old brew hitting the shelves this summer
New solar-cell efficiency record set
AIDS vaccine surprises scientists, proves partially successful
Is birth control the answer to environmental ills?
Editor's Pick
-
Adapting to the Freshwater CrisisForward-thinking experts are getting a better handle on the growing global water shortage and coming up with innovative approaches to ensuring the security, safety and sustainability of this resource
Space Newsletter
Get weekly coverage delivered to your inboxPodcasts
-
60-Second Earth
RSS ·
iTunes
The Jellyfish Menace
click to enable
-
60-Second Science
RSS ·
iTunes
Plants Share Light If Neighbor Is Related
click to enable
Slideshows
Fight to protect California condors from lead ammunition moves to Arizona
Circulation of LHC Beams Could Resume in Earnest over the Weekend
Measuring Up: New NIST Director, Plus Big Budget Put Measurement Science in Public Eye
How Long Can a Nuclear Reactor Last?
What to Do About Endocrine Disruptors? A Q&A with Linda Birnbaum



