Can You Spot It?

Don’t you hate it when random spots appear on your face for no reason at the worst possible time? To pop or not to pop, that is the question… luckily for you at least, the spot won’t stay there forever, unlike for a certain guy I know – a certain guy called Jupiter.

The gas giant, Jupiter, is well known for its Great Red Spot, a vast, swirling oval on the surface of the planet, which has baffled astronomers for hundreds of years by refusing to disappear. Countless theories have been produced which attempt to explain this oddity – it’s a molten lava lake; a new moon is emerging; it is an object floating on the surface of the planet; it is the top of a rising column of gas, and so on. The Voyager program launched in 1977 brought new light to this mystery, as astronomers could finally see in great detail the hurricane-like swirling flow of the spot, embedded amongst strips of horizontal winds enveloping the planet. The definition of ‘hurricane’, however, is unsuitable for this phenomena. Hurricanes on Earth are powered by the heat released when moisture above the oceans condenses to rain, and more importantly, only last for a couple of days at most before dissipating.

From the images, astronomers realised that Jupiter is practically a massive sphere consisting of dynamic fluids, unlike the solid planet they were looking for. The gases in Jupiter’s atmosphere are constantly flowing, driven by heat dissipated from deep within and by the planet’s own rotation, known as a Coriolis effect. This idea simply confused astronomers even more. How could something like the Great Red Spot exist with such apparent stability amongst a sea of turbulence? Even the spot itself is made up of the very same chaotic fluids, yet somehow it maintains its shape seemingly indefinitely.

In the early 1980s, a young astronomer and applied mathematician called Philip Marcus programmed a computer with a system of fluid equations, taking into account Jovian weather conditions and the planet’s fast rotation. His model, which was based on the fluid dynamics he had worked with for models of the Earth, produced a simulation of rotating vortexes coalescing into an oval with an uncanny resemblance to the spot on Jupiter. He described this as the ‘Pacman’ effect, where stronger vortexes tend to absorb weaker ones.

Dr Marcus has developed several ideas on the possible reasons for the spot’s stability over his years as an expert on the storm. He speculates that strong Coriolis forces on its sides hold the spot together. A dense cold lid of atmosphere above it pushing downwards and a warm buoyant floor of atmosphere that pushes upwards then make a vertical balance. Although an explanation for this phenomenon is still not available, scientists are learning more about the exotic conditions on Jupiter by making comparison to the Earth’s own weather. Many similarities between the stability of the spot have been made to Earth-based phenomena like vortexes formed from the Gulf Stream. Gaining an understanding of Jupiter’s atmosphere will allow us to understand Jupiters of other solar systems.

Let’s just hope you don’t form any indestructible spots this summer.


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