Planetary Science

Why Does Jupiter Have A Red Spot?

Jupiter's Great Red Spot is an anticyclonic storm in a persistent high-pressure region the size of Earth.

Josh Habka
Dec 21, 2022
5 min read
homeAstronomy 🔭Solar SystemJupiter

When you think about Jupiter (open in new tab), you probably picture either its immense size or the colored bands of gas that run down the side of it. Not only does the hulking gas giant look amazing, but multicolored bands of clouds run along its face. Or, you can consider an iconic storm, that enormous, swirling, red hurricane that is twice as big as the planet Earth (open in new tab) and has been the hallmark of our Solar System's largest planet since Earth's time over a century ago.

Those whirling bands are also what formed the iconic storm in the first place, and they are also what kept storms spinning for more than a century; Glenn Orton, a lead crew member on the Juno mission (opens in new tab) and NASA's Jet Propulsion Laboratory Planetary Scientist, told Business Insider (opens in new tab).

What is clear is that NASA's Juno mission has opened a new window into Jupiter's atmosphere, and the results challenge our understanding of Earth. While the answers are not yet crystalline, future missions to Jupiter are designed to study the atmosphere more thoroughly, and if all goes well, they will yield the answers scientists are looking for. In principle, additional clarity may arise from comparative studies of Jupiter's atmospheric dynamics with those of gas giants orbiting other stars. However, the latter is well beyond the scope of any Juno-like direct investigations.

Combined with microwave observations and gravitational measurements, Juno's latest findings will help scientists characterize Jupiter's atmospheric dynamics and how they cooled down over time, providing insights into the still-mysterious origins of gas giants in our own Solar System and beyond. Published Oct. 28 in Science, the latest findings from Juno measure the depths of Jupiter's fiercest storms, including its Great Red Spot - a whirlpool wider than Earth's width, which has been churning furiously for hundreds of years. The latest results, which came after years of sleuthing by colleagues, are now published in a series of papers that uncover the 3-D structure of Jupiter's meteorological system, including the well-known Great Red Spot, a centuries-old large storm enough to swallow Earth entirely.

Yet, in spite of Jupiter's latest findings, its famous Great Red Spot may yet be a pancake-like structure floating through the Jovian atmosphere, the spot being 12,000km wide and 40 times deeper. By combining data from 12 flights passing Jupiter's Great Red Spot - including two flights directly overhead - the paper's authors calculated where the storm is gathering most of the atmosphere's mass above Jupiter, which allowed them to estimate its depth. The instruments also observed two other storms, and although all three had roots that extended beyond the clouds' foundations on Jupiter, none reached down to as deep as the Great Red Spot.

Carlson said Jupiter's Great Red Spot was darker than the rest of the ammonia-rich cloud deck because clouds with ammonium hydrosulfide rose above the rest of Jupiter's clouds, then encountered more acetylene molecules, producing more red material. Below it is clouds of ammonium hydrosulphide, a compound that breaks down under temperatures found on Earth but is stable on Jupiter. White clouds are produced by the three, which, when struck by the radiation, break into molecules, which can combine to make compounds redder in appearance.

The origins of the red coloration are unknown; suggestions range from sulfur and phosphorus compounds to organic materials, which may have been produced from lightning discharges or photochemical reactions at high altitudes. The precise cause of the coloration has not been proven, but... laboratory experiments support the theory that the coloration is caused by complex organic molecules, red phosphorus, or another sulfur compound drawn from the depths within Jupiter. Some theories suggest the colors are caused by reactions between those chemicals in the Jovian atmosphere or from organic molecules struck by lightning.

The most popular ongoing theory is that cosmic rays, or sun ultraviolet radiation, react with ammonium hydrosulfide in Jupiter's atmosphere. One question is whether radiation from the Sun reacts with ammonium hydrosulfide in Jupiter's outer atmosphere to produce a deep red color. Through lab experiments, scientists believe this is due to compounds surrounding the planet, especially ammonia.

Like Earth, as colder gases flow downwards through Jupiter's atmosphere, the vortices get stronger, but Jupiter has no hard surface to slow down the vortices. The temperature of Jupiter's atmosphere is right at the point where a cloud of water forms about 65 kilometers down from the summit of the cloud. Jupiter's skies are 70km (44 miles) deep, consisting of layers of clouds made from ammonia ice, ammonium hydrosulfide, or water ice and vapor.

Known as the Great Red Spot, the Great Red Spot on Jupiter is visible from space and covers an area of more than 10,000 miles (16,000 kilometers) across Jupiter's atmosphere - roughly a third the diameter of the Earth. Its Great Red Spot has been around for far longer than the other storms on Jupiter, as it sits in the middle of two strong jet streams moving in opposite directions. In the case of this largest storm, it has extended for at least 200 miles in the clouds on Jupiter, past the depths at which clouds form and water condenses.

Cameras carried by the Voyager 1 and 2 spacecraft revealed in 1979 that the Great Red Spot rotates counterclockwise for approximately seven days, consistent with a wind speed of 400 kilometers (250 miles) per hour on its fringe. Careful monitoring of atmospheric features revealed that the red spot was rotating counterclockwise already as early as 1966, observations that were strongly confirmed by early time-lapse films of Voyager flybys. The Great Dark Spot was photographed by Voyager 2 in 1989 and could have been an atmospheric hole, not a storm.

The shorter observing history of this planet's location and its slower rate of development make them conclude they are one and the same. The longer gaps in observations for these phenomena make it hard to determine whether or not they are actually in the same spot. Whether the initial spot has disappeared and been reformatted, disappeared, or the observational record is just bad is unknown.

There are several possibilities the search points toward -- for example, vortex swings, variations in wind shear in the flow around the spot, and more complicated changes under Jupiter's clouds. What is New- Using data from the Juno mission, scientists who conducted a new study looked at the Great Red Spot's vertical structure and two other storms on Jupiter.

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Read More About Jupiter:

Why Does Jupiter Have So Many Moons?
Jupiter has many moons due to its strong gravitational pull, proximity to the asteroid belt, and large size.

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