Spots on the Outer Planets

[dougettinger]

What causes the spots on the surfaces of the outer planets ? Although spots have been observed not only on Jupiter but also Saturn and Neptune. I wish to specifically address the Great Red Spot on Jupiter but my questioning certainly applies to all spots.

The normal public is told that these spots represent storms in the atmosphere, but the Great Red Spot and other spots on Jupiter are stationary. Storms in the Earth's atmosphere are never stationary. They move on the surface due to Coroelis affects.

No mention to my knowledge is ever made that these spots could have been caused by collisions although some recent data supports this idea. I am refering to the pieces of comet that fell onto Jupiter's surface. The resulting spots looked very much like the Great Red Spot, but smaller versions and I believe different coloring. The spots survived for a significant amount of time which leads me to reason that the Great Red Spot is the result of a much more massive collision that is still surviving the few hundred years of its known existence.

Are there any other mainstream ideas except the one where a massive hurricane is nailed to the surface of Jupiter ?

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

The normal public is told that these spots represent storms in the atmosphere, but the Great Red Spot and other spots on Jupiter are stationary. Storms in the Earth's atmosphere are never stationary. They move on the surface due to Coroelis affects.

Where do you get the idea that the storm systems observed on gas giants are stationary? They are highly dynamic- they rotate, increase and decrease in intensity, and move with respect to other cloud systems.

[dougettinger]

This is an important insight for me. I realize that these storms rotate and do change somewhat in size and shape. But I thought that the Great Red Spot specifically maintained a fairly constant longitudanal and constant latitudunal location. Please confirm that this thinking is entirely incorrect; and, the GRS does move across Jupiter's surface longitudenally.

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

This is an important insight for me. I realize that these storms rotate and do change somewhat in size and shape. But I thought that the Great Red Spot specifically maintained a fairly constant longitudanal and constant latitudunal location. Please confirm that this thinking is entirely incorrect; and, the GRS does move across Jupiter's surface longitudenally.

Jupiter has no surface. Since it has a well defined axis of rotation, latitudinal coordinates are well established. But the concept of longitude is fuzzy; there are several systems in use. The most common is called System II, which reckons longitude based on the mean rotation of the north and south equatorial belts. (System II was originally based on the location of the GRS.)

The atmosphere itself rotates differentially- different latitudes have different rotation rates. This creates belts that tend to trap material (very different from the Earth, of course). So stable storms tend to stay at nearly the same latitude, and rotate with the belt of gases at their specific latitude. Nevertheless, the GRS does drift longitudinally even with respect to its own belt of atmosphere.

Fluid dynamics largely explains the position and movement of the GRS and other storm systems. The mystery is what mechanism allows these storms to be so stable (the GRS is at least a couple hundred years old, maybe more).

[neufer]

I thought that the Great Red Spot specifically maintained a fairly constant longitudinal and constant latitudinal location. Please confirm that this thinking is entirely incorrect; and, the GRS does move across Jupiter's surface longitudinally.

<<The Great Red Spot's latitude has been stable for the duration of good observational records, typically varying by about a degree. Its longitude, however, is subject to constant variation. Because Jupiter does not rotate uniformly at all latitudes, astronomers have defined three different systems for defining the longitude. System II is used for latitudes of more than 10°, and was originally based on the average rotation rate of the Great Red Spot of 9h 55m 42s. Despite this, the spot has "lapped" the planet in System II at least 10 times since the early nineteenth century. Its drift rate has changed dramatically over the years and has been linked to the brightness of the South Equatorial Belt, and the presence or absence of a South Tropical Disturbance.>>

[dougettinger]

I thought that the Great Red Spot specifically maintained a fairly constant longitudinal and constant latitudinal location. Please confirm that this thinking is entirely incorrect; and, the GRS does move across Jupiter's surface longitudinally.

<<The Great Red Spot's latitude has been stable for the duration of good observational records, typically varying by about a degree. Its longitude, however, is subject to constant variation. Because Jupiter does not rotate uniformly at all latitudes, astronomers have defined three different systems for defining the longitude. System II is used for latitudes of more than 10°, and was originally based on the average rotation rate of the Great Red Spot of 9h 55m 42s. Despite this, the spot has "lapped" the planet in System II at least 10 times since the early nineteenth century. Its drift rate has changed dramatically over the years and has been linked to the brightness of the South Equatorial Belt, and the presence or absence of a South Tropical Disturbance.>>

Thanks to both Chris and Neufer for this illumination. This excellent video which I have already seen can be a bit confusing; but, the measured lapping of the spot to System II overall rotation says it all. The spot is not stationary to longitude.

It is understood that the Red Spot still presents a mystery. My discussion does not end here. Chris mentioned that Jupiter has no surface. Actually, there is a zone somewhere well below the observed surface of gases where it is postulated that hydrogen is frozen due the combination of presssure and temperature. The outer edge of this zone even though it might move with respect to System II rotation could become that hidden surface where a possible, past impactor is lodged. ---just presenting some food for thought. I do not know about you, but I have a burning desire to have a reason for these spots.

Doug Ettinger
Pittsburgh, PA

[BMAONE23]

More Jupiter movies
http://www.solarviews.com/raw/jup/vjupitr1.mov
http://pds-rings.seti.org/jupiter/anima ... er_160.mov
Red spot dynamics
http://www.solarviews.com/raw/jup/vjupitr3.mov