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Wednesday, 17 November 2021

What has Juno found on Jupiter? Part I – Water and weather

One of Juno’s findings has been some measurements of the Great Red Spot – a giant Jovian storm that could fit three Earth-sized planets inside it. Although Juno has the power to image up to 350 km deep into the Jovian atmosphere, it turns out that the Great Red Spot is deeper than this. Measurements of its temperature show that, for the first 80 km, it is cooler than the surrounding atmosphere, and below that, it’s warmer. We don’t know why, but it could be linked to how the storm started, and whether it's permanent or will disappear with time.
The Great Red Spot has been observed for over 300 years now. It's so large it could accommodate three Earth-sized planets! Wikimedia Commons

Observations of "blades" and "flakes" spinning off into space suggest it might be nearing an end to its lifetime. Scientists have also seen something they called the Red Spot Hollow: a dark area surrounding the Great Red Spot. And it’s growing too.

A strange cyclonic region called the “brown barge” has been spotted in the southern hemisphere. This is unusual because these dark ovals are normally seen in the north equatorial belt and are usually hard to see, where this one stands out. They tend to be short-lived, disappearing as the cloud formations rearrange. We’re not sure why this one is different. Scientists are generally trying to work out why vortexes of cyclones form, and how they come to change into different geometric shapes, or suddenly vanish from sight!

New perturbation peaks followed by condensation (probably of ammonia) have been found that also raise questions – what are they and how did they form?

But this is not the only unusual weather formation Juno has studied on Jupiter. The Juno mission has also confirmed some unusual findings made by the Galileo mission in 1995 – and thwarted them!

The Galileo spacecraft threw a probe into the Jovian atmosphere and, for the hour before it was crushed, it recorded a much drier and windier environment than scientists thought Jupiter had. They assumed they’d found a desert. But Juno has since used microwave detectors to measure the water content, which works because water-ice clouds absorb microwaves, and found the dryness extends across the entire equatorial belt of Jupiter, where “pop-up” clouds indicate the tops of shallow lightning storms. They think these might be spots where the ammonia and water in the atmosphere dropped out as mushballs (Jovian hailstones). (In contrast, they also found there are more storms at the poles than equator…)

Galileo spacecraft. NASA.

Despite confirming the reality of Jovian deserts, Juno has also found more water than otherwise expected, ~0.25% of equatorial atmospheric molecules. It’s just that there’s not much atmospheric mixing: i.e. the water is not evenly distributed. In fact, it’s so unevenly distributed, scientists are wondering why.

The amount of water on Jupiter could tell us something very important for our solar system’s history: physicists think Jupiter was the first planet to form, and sucked up much of the gas, water, and dust leftover from the formation of the sun, so how much there is could lay the blueprint for the story of our world. And what we learn could be extended to other exoplanets, teaching us about how other systems formed.

For more information about Jupiter, check out our updated article, and look out for a part II blog on Juno’s findings, featuring it’s magnetic behaviour.

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