Much about the Great Red Spot is still unknown, including exactly when and how it formed, what gives it its striking red color and why it has persisted for so much longer than other storms that have been observed in the atmosphere of Jupiter. However, astronomers think that its position in latitude, consistently observed to be 22 degrees south of Jupiter’s equator, is connected to the prominent cloud bands in Jupiter’s atmosphere.
As a planetary astronomer who studies the atmospheres of comets, I’m normally not investigating massive storms. But I still want to know about the features seen in the atmosphere of other bodies in the solar system, including Jupiter. Studying atmospheres of all kinds deepens our understanding of how they form and work.
Unlike Jupiter, the Earth has land masses that cause major storms to lose energy due to friction with a solid surface. Without this feature, Jupiter’s storms are more long-lasting. However, the Great Red Spot is long-lived, even by Jupiter standards. Researchers don’t quite understand why, but we do know that Jupiter’s storms that are located in cloud bands with the same direction of rotation tend to be longer lasting.
The Great Red Spot is confined by an eastward jet to its north and a westward jet to its south, confining the storm to a constant latitude. However, the Great Red Spot has undergone considerable changes in longitude over time, and recent evidence suggests that its rate of westward longitudinal motion is increasing.
Like the Great Red Spot, the bands have undergone little change in latitude over the time during which they have been observed. Researchers don’t entirely understand the banded structure, but we do have evidence suggesting that the light colored zones are regions of rising material, and the dark belts are regions of material sinking into the atmosphere.
On Earth, there is a well-defined boundary between the atmosphere and the surface of the planet, which is largely covered by liquid water. However, there are no known large oceans of water under Jupiter’s clouds. Based on what researchers do know, the atmosphere smoothly transitions to a liquid hydrogen interior within the planet. There may be a solid core to Jupiter, but it is most likely buried very deep under a thick layer of liquid metallic hydrogen, a form of hydrogen that acts as an electrical conductor.
What else do we know about the Great Red Spot that is changing dramatically? Its size, shape and color. An analysis of historical and recently obtained data on the Great Red Spot has shown that it is shrinking and becoming both rounder and taller, and its color has also varied over time. What is driving these changes, and what do they mean for the future of the Great Red Spot? Researchers aren’t sure.
However, NASA’s Juno spacecraft, currently orbiting Jupiter, is gathering more data on the cloud bands and the Great Red Spot. These new data will likely provide insights into many of the features in Jupiter’s atmosphere.