View Full Version : Saturn Slowing

The Supreme Canuck
2003-Jun-16, 08:32 PM
Have you guys heard about this? Apparently Saturn's winds are slowing down. About a 40% reduction in velocity at the equator. I don't have a link, I'm reading it in a newspaper. Do they have it right or is it just bunk?

2003-Jun-16, 08:54 PM
I don't know... guess we'll know for sure when Cassini arrives next year, but it seems a bit ridiculous. 40% is a huge number.

Or, perhaps it's a temporary/seasonal thing.

2003-Jun-16, 09:02 PM
Well, here's a link to a CNews story (http://cnews.canoe.ca/CNEWS/Space/2003/06/13/110615-ap.html), byline Associated Press, which supports what you heard:

"(AP) - Astronomers say the winds of Saturn appear to be slowing dramatically just as NASA's Cassini spacecraft approaches the ringed gas planet. Other researchers who study giant planets say the finding is surprising because little change has been detected in the winds of neighbouring planets like Jupiter."

"A comparison of images taken from one of the Voyager missions in the early 1980s and photos taken by the Hubble Space Telescope from 1996 to 2002 indicate that winds have slowed by about 40 per cent at the equator of Saturn."

The Supreme Canuck
2003-Jun-16, 09:16 PM
Well, that doesn't just support it, it IS it! The exact article I read! I have to admit though, 40% does sound rather large...

2003-Jun-16, 10:28 PM
I read this on the Inet too. What I read said that nobody knew why the winds are slowing down. As mentioned above, we'll just have to wait for Cassini to tell us.

In the mean time, it is MHO that it is just normal gusting like we get here on good ol' Earth. :D

2003-Jun-16, 10:31 PM
Am I the only one who read that and immediately thought, "Oh no!! It's a rotation stoppage!!"


Saturn must be bobbling, too...

Donnie B.
2003-Jun-16, 10:57 PM
Science News had an article about this too. The speculation is that it's seasonal, but that's a surprise too, if true -- the Sun's not supposed to have that much effect at Saturn's distance.

Another possibilty is that it's an artifact of the data. The high-speed measurements are from Voyager, the lower are from Hubble -- and they may have measured wind speeds at different altitudes (higher-altitude winds are slower on Saturn).

The Supreme Canuck
2003-Jun-16, 11:01 PM
The headline in my paper said something about the winds being slower in the shadow of the rings. No idea what that's about...

2003-Jun-16, 11:17 PM
I'd vote for the error in the measurements as the most likely cause of the apparent change, but we'll find out for sure when Cassini gets there.

Tim Thompson
2003-Jun-17, 01:09 AM
A strong decrease in Saturn's equatorial jet at cloud level
A. Sanchez-Lavega, et al.
Nature 423(6940): 623-625, June 5, 2003
Abstract: The atmospheres of the giant planets Jupiter and Saturn have a puzzling system of zonal (east-west) winds alternating in latitude, with the broad and intense equatorial jets on Saturn having been observed previously to reach a velocity of about 470 m/s at cloud level. Globally, the location and intensity of Jupiter's jets are stable in time to within about ten per cent, but little is known about the stability of Saturn's jet system. The long-term behaviour of these winds is an important discriminator between models for giant-planet circulations. Here we report that Saturn's winds show a large drop in the velocity of the equatorial jet of about 200 m/s from 1996 to 2002. By contrast, the other measured jets (primarily in the southern hemisphere) appear stable when compared to the Voyager wind profile of 1980-81.

I have read the paper, and I don't think there is any problem with the measurements. It's only the equatorial jet that has slowed, and there's no really good reason why it can't do that. Remember that Neptune's "great blue spot" seen by Voyager, had vanished by the time the HST looked at Neptune. Planetary atmospheres are by their nature variable, and should be expected to display many variable & transient features.

The wind speed is derived by measuring cloud motions on HST images. If the clouds form at a higher altitude now than in Voyager's day, they will move more slowly, even though the actual wind speed as a function of altitude remains unchanged. But other evidence, such as the motion of large storms, argues against that.

Heating by sunlight is not negligible, and is complicted by the strong oblateness of the planet. The poles fall into shadow twice each Saturn year, and the variable shadow of Saturn's ring changes equatorial heating over the Saturn year. The extent to which these or other effects might affect the wind speed is not known. There was no attempt in the paper to explain why the winds slowed as much as they did.

The Supreme Canuck
2003-Jun-17, 01:14 AM
Makes sense, just seemed kind of "funky" when I read it in the paper, if you know what I mean... Thanks for the info, it explains it quite well. I guess we will have to wait for Cassini...

2003-Jun-24, 07:45 AM
Am I the only one who read that and immediately thought, "Oh no!! It's a rotation stoppage!!"


Saturn must be bobbling, too...

I know I did. :)

Maybe Nancy is just picking up signals that were supposed to go to Saturnians.