Great Red Spot of Jupiter

Jupiter's Great Red Spot is one of the solar system's most fascinating features — a massive storm that's been raging for roughly 190 years. It's wide enough to swallow Earth whole, with winds reaching 500 miles per hour. The storm sits in Jupiter's southern hemisphere and extends 500 kilometers beneath the cloud tops. There's still plenty more to uncover about this extraordinary, swirling giant.

Key Takeaways

• The Great Red Spot is a massive, long-lived storm on Jupiter's southern hemisphere, with winds raging at 500 miles per hour.
• Despite shrinking steadily, the storm still measures roughly 10,159 miles wide, large enough to swallow Earth entirely.
• The storm extends 500 kilometers beneath Jupiter's cloud tops, dwarfing any storm system found on Earth.
• The Great Red Spot has persisted for approximately 190 years, forming as a separate system from earlier documented spots.
• Its latitude remains remarkably stable within 1°, though its longitude drifts constantly relative to surrounding atmospheric bands.

What Is the Great Red Spot?

The Great Red Spot is a long-lived, enormous storm system on Jupiter and the most conspicuous feature of the planet's visible cloud surface. You can think of it as a gigantic hurricane, but its storm dynamics differ considerably from Earth's. It's an anticyclone — a high-pressure system that sustains a persistent, self-reinforcing storm.

Unlike Earth's hurricanes, it has no ocean or solid surface driving it; Jupiter is fluid throughout, and atmospheric composition plays a key role in powering the storm through condensation. The spot appears generally reddish and slightly oval in shape. It sits in Jupiter's southern hemisphere, where opposing jet streams trap it in place. Its winds, central calm eye, and massive scale make it one of the solar system's most remarkable atmospheric phenomena. At its periphery, wind velocities can reach approximately 400 km per hour.

Scientists believe the Great Red Spot was first observed 300 years ago, making it one of the longest-lasting storm systems ever recorded in our solar system.

How Big Is the Great Red Spot?

Now that you know what the Great Red Spot is, let's talk about its sheer scale. Today, it measures roughly 10,159 miles wide, still enough to engulf Earth. However, size fluctuations over time tell a dramatic story.

Voyager 1 and 2 clocked it at 14,500 miles across in 1979, and Hubble recorded 13,020 miles in 1995. It's been shrinking at approximately 930 kilometers per year. Interestingly, as the storm grows taller while shrinking, its vertical dimension continues to increase even as its width decreases.

Historical size extremes paint an even more striking picture. In the late 1800s, the storm stretched nearly 41,000 kilometers, swallowing Earth three times over. Now, recent Hubble measurements confirm it's reached its smallest size in observational history, recording just 8,700 miles wide and 5,800 miles high — barely spanning a single Earth diameter. Since 2012, the shrinkage rate has accelerated to 580 miles per year, a change first detected through amateur observations before being confirmed by researchers.

Where Does the Great Red Spot Sit on Jupiter?

Sitting in Jupiter's southern hemisphere, the Great Red Spot holds a remarkably fixed position at roughly 22°S latitude — about 20 degrees below the equator. Its latitude stability is one of its most striking traits, varying by only about 1° across centuries of observation.

Its longitude behavior, however, tells a different story:

1. Longitude drifts constantly relative to surrounding atmospheric bands
2. A ~1° amplitude oscillation repeats on a 90-day cycle
3. Each degree of greater longitude shifts transit timing by 1⅔ minutes
4. Monthly drift runs approximately 1.75° in System II coordinates

You can think of it as anchored north-to-south but sliding east-to-west, trapped within Jupiter's fastest westward jet stream while rotating counterclockwise deep in the southern atmosphere. The spot is further confined by a modest eastward jet stream to its south, creating a boundary that helps define and preserve its position within the Jovian atmosphere. With winds raging at 500 miles per hour, the Great Red Spot maintains its status as the largest known storm in the solar system.

How Deep Does the Great Red Spot Actually Go?

After centuries of watching the Great Red Spot churn across Jupiter's southern hemisphere, scientists finally have a number for how deep it actually goes: 500 kilometers beneath the cloud tops. NASA's Juno spacecraft confirmed this by detecting subtle shifts in its line-of-sight velocity caused by the vortex's localized density anomalies, revealing the storm's internal structure dynamics for the first time.

For comparison to earthly storms, Jupiter's Great Red Spot dwarfs anything you'd find on Earth — an equivalent storm would stretch from the ground to the International Space Station. Yet despite its scale, it's actually shallower than Jupiter's jet streams, which plunge to 3,000 kilometers deep. The Great Red Spot stays confined to the upper atmosphere, never penetrating the planet's deeper circulation layers. The depth measurement became possible through a dedicated Juno flyby, where the spacecraft flew directly above the Great Red Spot to capture precise gravity readings used to calculate the storm's mass and extent.

Juno has been orbiting Jupiter since 2016, completing 37 flybys that have collectively transformed our understanding of the planet's atmospheric structure and storm systems.

How Old Is the Great Red Spot?

Few questions about Jupiter's Great Red Spot spark more debate than its age. You might assume it's ancient, but modern research tells a more complex story. Frequency of observation gaps and size comparison over centuries reveal two likely distinct storms:

1. Cassini documented a "Permanent Spot" beginning in 1665
2. Observations ceased around 1713, creating a 118-year gap
3. A new reddish oval reappeared in 1831 at the same latitude
4. Historical sketches show the earlier spot was one-third to one-half smaller

Scientists publishing in Geophysical Research Letters (2024) concluded it's "highly unlikely" today's Great Red Spot is Cassini's original feature. The current storm has persisted roughly 190 years, emerging as an entirely separate atmospheric system. Researchers believe the GRS formed through wind instability mechanisms that created elongated cells capable of trapping atmospheric winds into a stable, long-lived vortex.

Computer simulations suggest that a disturbance between opposing jet streams could have generated the conditions necessary for the Great Red Spot to form as an independent storm system.

Why Is the Great Red Spot Red?

While the Great Red Spot's age remains a point of scientific debate, its color raises an equally puzzling question: why is it red? Scientists haven't pinpointed the exact chemical composition responsible, but leading theories point to acetylene and ammonia as key contributors.

These chemicals alone can't produce the red color, though. Ultraviolet light plays an indispensable role by triggering photolysis, causing chemicals to react and form reddish materials. Ammonium hydrosulfide, found deep beneath Jupiter's clouds, may also react with UV radiation or cosmic rays to produce color-altering compounds.

The atmospheric conditions within the spot keep concentrations of these compounds high, intensifying the color. Laboratory experiments and data from the Cassini spacecraft support UV-driven mechanisms, though multiple chemical factors are likely responsible rather than any single compound. Convection within Jupiter's atmosphere dredges up these chemicals from lower layers, where they are then exposed to sunlight and irradiated to produce the reddish aerosols observed in the spot.

Despite ongoing research, the reason for the red color remains unclear, with photochemical products like smog among the competing explanations scientists continue to investigate.

How Fast Are the Great Red Spot's Winds?

When you consider that Jupiter's Great Red Spot dwarfs Earth in size, its wind speeds become all the more staggering. The storm's outer ring exceeds 400 mph, while its center remains nearly calm—a dramatic wind variation that mirrors hurricane structure.

Hubble data confirmed sustained wind acceleration of roughly 8 percent between 2009 and 2020, less than 1.6 mph annually. Smallest detectable features resolved by Hubble span approximately twice the length of Rhode Island.

Here's what defines the storm's wind behavior:

1. Outer boundary winds surpass 400 mph counterclockwise
2. The innermost region shows stagnant, minimal airflow
3. One full rotation completes every six Earth days
4. An abrupt speed change occurred during a 2017 convective storm event

Detecting these subtle shifts required eleven continuous years of Hubble monitoring—precision impossible with conventional observation methods. The observations used to study these winds were captured on September 20, 2020, when Jupiter was approximately 4.36 AU from Earth.

Is the Great Red Spot Shrinking?

One of Jupiter's most striking features is getting smaller, and scientists have tracked this transformation for over 150 years. In the late 1800s, the Great Red Spot stretched 41,000 kilometers across. By 2018, it had shrunk to roughly 10,250 miles — the smallest ever recorded, narrowing about 580 miles per year since 2012.

Its shape has shifted too, evolving from oval to circular, while its internal dynamics continue changing. Small eddies alter how energy moves within the storm, and fewer smaller storms are feeding it. Hubble's 2023–2024 data revealed it jiggles through an oscillation cycle, expanding and contracting like gelatin.

Scientists expect it to eventually stabilize in a less-elongated form, though no single explanation fully accounts for its accelerating shrinkage. Caught between two opposing jet streams, the storm has managed to sustain itself for centuries despite its ongoing decline. These observations are part of the Outer Planet Atmospheres Legacy program, which aims to better understand the mechanisms driving the largest storms in the solar system.

Will the Great Red Spot Eventually Disappear?

The Great Red Spot is shrinking — but will it actually vanish? Scientists aren't certain, but the long term changes in great red spot dynamics point toward significant transformation.

Here's what researchers predict:

1. The storm could become a "Great Red Circle" within a decade.
2. Complete disappearance may occur within 20–30 years.
3. Simulations suggest a third giant spot could eventually emerge.
4. Small eddies are accelerating internal changes, affecting the future impact of great red spot disappearance on Jupiter's atmospheric behavior.

History supports this concern — a similar permanent spot observed from 1665 to 1713 vanished for 118 years. The Great Red Spot may share that fate, though Jupiter's deep atmosphere could sustain it longer than expected. In the late 1800s, the storm measured over 35,000 miles wide, making its current size of under 10,159 miles a dramatic illustration of just how much has already been lost. The study tracking these changes was published in Geophysical Research Letters in 2024, lending significant scientific weight to predictions about the storm's uncertain future.