APOD: Saturns Hexagon Comes to Light (2009 Dec 14)

[APOD Robot]

Saturns Hexagon Comes to Light

Explanation: Believe it or not, this is the North Pole of Saturn. It is unclear how an unusual hexagonal cloud system that surrounds Saturn's north pole was created, keeps its shape, or how long it will last. Originally discovered during the Voyager flybys of Saturn in the 1980s, nobody has ever seen anything like it elsewhere in the Solar System. Although its infrared glow was visible previously to the Cassini spacecraft now orbiting Saturn, over the past year the mysterious hexagonal vortex became fully illuminated by sunlight for the first time during the Cassini's visit. Since then, Cassini has imaged the rotating hexagon in visible light enough times to create a time-lapse movie. The pole center was not well imaged and has been excluded. This movie shows many unexpected cloud motions, such as waves emanating from the corners of the hexagon. Planetary scientists are sure to continue to study this most unusual cloud formation for quite some time.

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[kovil]

I believe that the well studied scientific discipline of fluid dynamics has a fairly good understanding of why a hexagonal shape will self generate when under rotational vector forces.
I read some very good analysis on another discussion board a year ago. Surprising that mainstream astrophysics is so ignorant about this.

[harry]

G'day Kovil

What is mainstream?

[jerbil]

I think you raise an important point, Harry.

The term “mainstream” can only refer to the bulk feeling of scientific opinion in whichever discipline. The accuracy of such a feeling, whether advanced by the editors of reputable journals, or merely being general thought of by scientific persons, may be accurate, but sometimes not.

Unfortunately, one cannot necessarily immediately detect between those who are merely incorrect, those who are mentally unbalanced, and those who have a valid case to make.

[CatchDude]

Why is the central part blacked-out artificially? Is it because the picture of the hexagon shaped cloud is made up out of multiple pictures which did not include the centre, is the centre maybe unusually brightly lid so it had to be blacked out just like the sun is on the SOHO lasco pictures? Or is there another reason? And if it's because the centre has not been imaged: Why not?

[bystander]

@Catchdude

The pole center was not well imaged and has been excluded.

The visible-light cameras of Cassini's imaging science subsystem, which have higher resolution than the infrared instruments and the Voyager cameras, got their long-awaited glimpse of the hexagon in January, as the planet approached equinox. Imaging team scientists calibrated and stitched together 55 images to create a mosaic and three-frame movie. The mosaics do not show the region directly around the north pole because it had not yet fully emerged from winter night at that time.

[neufer]

http://asterisk.apod.com/viewtopic.php?f=9&t=15074

[geckzilla]

Art, do you remember where that video was of an example of a mini hexagonal formation? I forget if they used liquid or smoke. I tried searching for it but but not have the correct keywords.

[neufer]

Art, do you remember where that video was of an example of a mini hexagonal formation? I forget if they used liquid or smoke. I tried searching for it but but not have the correct keywords.

Most certainly it was a rotating annulus fluid convection video such as:

http://tinyurl.com/yb45ou7

[geckzilla]

Hmm, maybe so. The one I remember specifically created a hexagon in a very similar way to Saturn's, though. None of these really resemble it.

[davewstorer]

Back in the early '60s, I had a student job working with a meteorologist, Dr. Fred Bates, doing thunderstorm research. One of my jobs was to plot the 500mb line around the north pole and then determine a three-day moving average. The 500mb line was a good indicator of where the jetstream lay. Dr. Bates explained that the jetstream tended to fall into patterns with an integer number of waves around the pole. The integer ranged from 4 to occasionally 7. The four and five wave patterns were the most stable, and sometimes in the summer a 4-wave pattern would lock in for one or two months, with some variation but definitely the same number of waves per circuit.

The first time I saw the Saturn hexagon, I said to myself, "That looks just like the 6-wave pattern I used to see sometimes in the spring and fall, when the weather was the most changeable." The 6 and 7 wave patterns here on Earth were quite unstable and never lasted for more than a few days. With the perfectly uniform conditions on Saturn, I can see how one of these patterns could get locked in and remain for a long time.

Happy Holidays,
Dave

[david g. t. curran]

I believe that the hexagonal shape of the clouds shown for Saturn is due to free convection effects from a heated surface to a colder surface. This is a well-known heat transfer effect that has a large literature on the phenomena.
David G.T. Curran

[Chris Peterson]

I believe that the well studied scientific discipline of fluid dynamics has a fairly good understanding of why a hexagonal shape will self generate when under rotational vector forces.
I read some very good analysis on another discussion board a year ago. Surprising that mainstream astrophysics is so ignorant about this.

I see nothing to suggest that the people studying this effect are ignorant of fluid dynamics. There are several suggestions as to what might cause such a phenomenon, and the goal in studying these images and working with models is to fully understand the causes, and also to use this as a probe for conditions inside Saturn that are otherwise difficult to measure.

Saturn isn't the easiest lab in the world to work in!

[peter2718]

How big is this structure? It would be interesting to know the radii of the outer circle and the radius of the blanked out region in the picture. In terms of the radius of Saturn or equivalently the angles subtended at the centre.
Peter.

[neufer]

How big is this structure? It would be interesting to know the radii of the outer circle and the radius of the blanked out region in the picture. In terms of the radius of Saturn or equivalently the angles subtended at the centre.

<<A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images. Unlike the north pole, HST imaging of the south polar region indicates the presence of a jet stream, but no strong polar vortex nor any hexagonal standing wave. However, NASA reported in November 2006 that the Cassini spacecraft observed a 'hurricane-like' storm locked to the south pole that had a clearly defined eyewall. This observation is particularly notable because eyewall clouds had not previously been seen on any planet other than Earth (including a failure to observe an eyewall in the Great Red Spot of Jupiter by the Galileo spacecraft).

The straight sides of the northern polar hexagon are each about 13 800 km long. The entire structure rotates with a period of 10h 39 m 24s, the same period as that of the planet's radio emissions, which is assumed to be equal to the period of rotation of Saturn's interior. The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere.

The pattern's origin is a matter of much speculation. Most astronomers seem to think some sort of standing-wave pattern in the atmosphere; but the hexagon might be a novel sort of aurora. Polygonal shapes have been replicated in spinning buckets of fluid in a laboratory.>>

It looks like the north polar region of Saturn has a lot of those
spirally things seen over Norway.

[CatchDude]

With those walls slightly curving inward, it kind of reminds me of the shapes you get when putting a sheet over a speaker that's laid down on its back and then putting some sand on it. Once you run some sound-pulses through them, you get these strange shapes made of sand with curved 'legs' which move and change with every change of frequency... Could it be that some sort of frequent pulse in the magnetic field causes the shape, or maybe some weird 'tectonics' around the pole generates said pulse? (If saturn has any tectonic activity at all...)

[neufer]

[kovil]

"Could it be that some sort of frequent pulse in the magnetic field causes the shape . ."

I think you're on to the correct path of discovery 'CatchDude' !
The hexagon shape at Saturn's pole is due to some kind of harmonic within Saturn.
Perhaps within the atmospheric density itself, or in the electric/magnetic activity,
or an interaction of all three. And the Coriolis effect contributing as well.

"The straight sides of the northern polar hexagon are each about 13 800 km long. The entire structure rotates with a period of 10h 39 m 24s, the same period as that of the planet's radio emissions, which is assumed to be equal to the period of rotation of Saturn's interior. The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere.

The pattern's origin is a matter of much speculation. Most astronomers seem to think some sort of standing-wave pattern in the atmosphere; but the hexagon might be a novel sort of aurora. Polygonal shapes have been replicated in spinning buckets of fluid in a laboratory." [1]

[1]"Geometric whirlpools revealed". Nature. May 19, 2006. http://www.nature.com/news/2006/060519/ ... 15-17.html. Retrieved April 27 2007. Bizarre geometric shapes that appear at the centre of swirling vortices in planetary atmospheres might be explained by a simple experiment with a bucket of water but correlating this to Saturn's pattern is by no means certain.

"The visible features on Saturn rotate at different rates depending on latitude, and multiple rotation periods have been assigned to various regions (as in Jupiter's case): System I has a period of 10 h 14 min 00 s (844.3°/d) and encompasses the Equatorial Zone, which extends from the northern edge of the South Equatorial Belt to the southern edge of the North Equatorial Belt. All other Saturnian latitudes have been assigned a rotation period of 10 h 39 min 24 s (810.76°/d), which is System II. System III, based on radio emissions from the planet in the period of the Voyager flybys, has a period of 10 h 39 min 22.4 s (810.8°/d); because it is very close to System II, it has largely superseded it.

However, a precise value for the rotation period of the interior remains elusive. While approaching Saturn in 2004, the Cassini spacecraft found that the radio rotation period of Saturn had increased appreciably, to approximately 10 h 45 m 45 s (± 36 s).[2] The cause of the change is unknown—it was thought to be due to a movement of the radio source to a different latitude inside Saturn, with a different rotational period, rather than because of a change in Saturn's rotation.

Later, in March 2007, it was found that the rotation of the radio emissions did not trace the rotation of the planet, but rather is produced by convection of the plasma disc, which is dependent also on other factors besides the planet's rotation. It was reported that the variance in measured rotation periods may be caused by geyser activity on Saturn's moon Enceladus. The water vapor emitted into Saturn's orbit by this activity becomes charged and "weighs down" Saturn's magnetic field, slowing its rotation slightly relative to the rotation of the planet itself. At the time it was stated that there is no currently known method of determining the rotation rate of Saturn's core.[3][4][5]

[2] "Scientists Find That Saturn's Rotation Period is a Puzzle". NASA. June 28, 2004. http://www.nasa.gov/mission_pages/cassi ... 62804.html. Retrieved 2007-03-22.
[3] NASA Jet Propulsion Laboratory (March 22, 2007). "Enceladus Geysers Mask the Length of Saturn's Day". Press release. http://saturn.jpl.nasa.gov/news/press-r ... newsID=733. Retrieved 2007-03-22.
[4] "The Variable Rotation Period of the Inner Region of Saturn's Plasma Disk". Science. March 22, 2007. http://www.sciencemag.org/cgi/content/a ... 6/5823/442. Retrieved 2007-04-24.
[5] "A New Spin on Saturn's Rotation". Science. April 20, 2007. http://www.sciencemag.org/cgi/content/a ... 6/5823/442. Retrieved 2007-04-24.

[bystander]

In Re to: What is Mainstream ?

To me 'mainstream science' is whoever it is that disseminates news stories to the public media that all have the same 'spin', in terms of ideology or what is 'real' according to 'science'. Like black holes, neutron stars, magnetic reconnection, and now in the case of comets -magnetic disconnection, gravitational lensing, neutrinos, frozen-in magnetic fields, the assumption that there is 'no charge separation' in space and thusly there can be 'no electric currents' in space whatsoever. These are all, in my opinion, erroneous conclusions that have been developed from incorrect assumptions made by mainstream astrophysics. Yet you can read all about them in the public media ad neauseum on almost a daily basis.

Mainstream science is the consensus. It is what the majority of scientist and the preponderance of evidence support. As someone who is going against the stream, the burden of proof is upon you. You should expect to have to provide evidence and support for your views (in your words, not a long list of papers). You should expect to have to answer the hard questions about how and why your alternative is better than generally accepted one. As yet, I have failed to see you do that when challenged. So, until you are ready to do so, I strongly suggest you drop references to EU and PC and stick with the mainstream. This is a mainstream forum. There are forums available for your viewpoints. This is not one of them. You won't get another warning.

[Chris Peterson]

Re: neutrinos, which were developed by nuclear physics; they are merely a metaphore to describe the 'missing' energy density/mass that is observed in particle accellerator photo plates after experiments. Neutrinos don't actually exist as particles tho.

Utter rubbish. We have detectors that specifically capture and record neutrinos. They're about as hypothetical as electrons.

It' s like the description John L. Dobson likes to use: "A neutrino is the pirrohuette that left the stage without the dancer." ! lol

Well, John Dobson's ideas about cosmology and physics are largely absurd. Not a good reference for quotes on the subject!

[Frenchy]

Here's another one straight from my imagination...how about a slightly magnetized neutron star interacting with Saturn's ionizing gases. (The neutron star being inside Saturn) I'm not even sure if that is possible...

[geckzilla]

If a neutron star were anywhere near Saturn, let alone inside of it, there probably would be no Saturn. Or us?

[mesinik]

One possible bet (not so bad at all): what if the Saturnian scientists built a big quantum supercomputer in the northern areas, inside of a hexagonal fridge; the clouds keep running along the cold front created by this refridgerator... like any self-respecting cloud will do under certain circumstances. (Of course, that big computing machinery is in work to find out the exact value of Pi & when they get it, they will build a round fridge for the computer so alien civilizations can´t see them from space).
This is a hypothesis which I would like to believe. If I would get some help for this task here at APOD forum, I might probably succeed in it (believing that) after some Christmas porter beers. Or maybe, this might be an edifying, mind-improving short story for a broad audience? But regrettably, when the porter runs out, the brain asks for different theories.
To keep it short, I would ask could there (under the upper atmospheric cover) be 6 other big whirls around the northern, visible one? Could a swirl of that size, at these latitudes be somewhat "normal" and stable because of Saturnian size, rotating speed & other conditions? This could probably make stable the hexagonal shape. It's somewhat strange but many other possible ways look even more like "Ersatzkaffee". If so, we probably don't need any more of a hexagonal continent of cold? Or am I wrong with that? Or could a hexagonal continent even be shaped in such a way? (If so, the "continent" might be even softer than a glacier.) To demonstrate it in maths, this is quite a hard task, isn't it?

[Lostinspace]

When i first saw it, the first thought that came to mind was that it is a gigantic alien lifeform that exists in Saturn's atmosphere.