The Great Red Spot (GRS) on Jupiter is shrinking and has been doing so for years. Now, however, it appears that the rate of shrinkage is increasing. The GRS is an anti-cyclonic storm in the planet’s southern hemisphere which has been under visual observation for at least 400 years. The original estimation of the size of the storm in the late 1800s determined the size to be approximately 25,500 miles across its widest point. Since the 1930s, astronomers have been documenting the size of the spot to follow any change.
Between 1979 and 1980, NASA’s Voyager 1 and Voyager 2 measured the area at 14,500 miles, a significant decrease from the original estimation of 25,500. Recently, NASA’s Hubble Space Telescope has been employed to determine the current size of Jupiter’s most well-known feature. What was found was that the current size of the storm is not nearly as large, measuring in at only 10,250 miles wide. Observations for the past several years indicate that the red storm spot on Jupiter is shrinking at almost 580 miles every year, roughly equal to the distance from Chicago to Washington, D.C.
At this time, scientists are attempting to determine whether the red storm will continue to shrink or if the size changes are simply part of normal fluctuations. The size is currently about half of what it was a mere 100 years ago. If the shrinkage continues at the present rate, it is estimated that the spot will no longer be oval, but will become circular by the year 2040, although many experts argue that this will not occur due to the distortions created by the nearby jet streams.
Not only has the size been diminishing, but the period of rotation has been changing. Currently, the anti-cyclonic, or counter-clockwise, storm fully rotates every six days Earth time. The wind on the edges of the storm can create gusts up to 268 miles per hour, but it appears that the interior is mostly stagnant. Data suggests that the other clouds on the planet are not only warmer, but approximately 5 miles lower in the atmosphere than the GRS. The red spot is unable to migrate either north or south due to strong opposing jet streams, but it frequently moves either east or west. In fact, since the 19th century, the storm has gone around Jupiter at least 10 times.
The GRS has varying degrees of color, from dark red to light salmon and even white. Sometimes the spot disappears altogether from the visible spectrum and can be seen only when it is in the SEB, or the South Equatorial Belt. Oddly, when the red spot is coupled with the SEB, it takes the opposite light attributes. When the GRS appears dark, the SEB is bright white and when the GRS appears light, the SEB is dark. There are still only theories as to why the storm is red, or various shades and hues of red, but the prevailing theory is that the color changes due to environmental factors such as temperature and complex organic molecules.
In conjunction with not having more than theories on why the color of the spot appears as it does, there are only theories as to what is responsible for the increase in shrinkage of the area. Scientists have theorized that eddies are changing the storm’s dynamics because they are feeding into it. The fact that the eddies have been documented as combining into the storm has not been enough to determine what, if any, changes they are causing. The fact remains that the Giant Red Spot on Jupiter is shrinking and scientists are diligently studying it to determine specific causes.
By Dee Mueller
on twitter @TuesdayDG