NASA has published beautiful new pictures from humanity’s closest meeting with Jupiter’s splendid Great Red Spot. On July 11, the Juno spacecraft flew around 5,600 miles above the swirling maelstrom – so close that we were given an unparalleled view of the 10,000 mile-wide storm.
The pictures, rapidly processed by an army of talented citizen scientists, disclose the spiral of red clouds within the spot and the deep red, central “core” where the winds are the peaceful. We see unbelievable details, including networks of fuzzy clouds, swirls and eddies forming shadows – even fine waves at the edges of the spot.
But despite the fact that the spot is so familiar to most of us, there’s a lot that we still don’t comprehend about it. These new Juno observations may lastly start to undo its mysteries.
1. How long has it been there?
The Great Red Spot is a long-lived, rotating vortex. Even Victorian-era astrophysicists delivered cautiously drawn pictures and explanations of the large red mark on Jupiter’s clouds. But it might have existed for even longer than that. Observations by 17th-century astrophysicists Robert Hooke and Giovanni Cassini propose a similar feature, so it might have been around for nearly four centuries – or longer. But what has kept it going for so many human lifetimes, and why is there no other vortex that comes near to matching it?
2. It’s shrinking, but is it dying?
We’ve known that the spot is lessening for many years, as the size measured by Earth-based and space-based observatories (comprising Hubble) has been pursued over time. Voyager measured a width of 15,534 miles in 1979, but that’s now reduced to as small as 9,942 miles only just wider than the 7,891 miles diameter of the Earth. But the shrinking has been neither constant nor uniform – the spot went through a period of quick shrinkage between 2012 and 2014, but has now seemed to stabilize at the new smaller size. Who knows whether we’ll ever see the death of the spot, or whether it will continue to be an everlasting fixture of Jupiter’s churning atmosphere.
3. What is fueling it?
The Great Red Spot rolls like a ball bearing between two of Jupiter’s prominent bands, whose atmospheric jet streams act as conveyor belts for minor storm clusters, eddies and vortices. Though if these storms are unfortunate enough to meet the Great Red Spot, they are consumed by it. Maybe these smaller vortices deliver the extra energy and angular momentum required (rotational energy locked up in orbital motion and spin) to endure the swirling maelstrom – but we can’t know for sure.
The mix of gases and clouds discovered within the spot also proposes there is a powerful upsurge (known as an upwelling) at the centre, which could be carrying heat upwards to sustain the vortex. The new high-resolution pictures show the core of the storm as a deep red color, with delicate detail that will teach us more about the dynamics within the heart of the spot.
4. How deep does it go?
If you were somehow capable of flying a balloon at the edge of the spinning storm, you’d be blown around the vortex in about 3.5 days. Yet, the Great Red Spot is not quite the same as a cyclone: there’s no ocean underneath to sustain the energy of it, and nobody really knows how far down it prolongs into the deep atmosphere. Is it just a feature in the upper clouds? Or could it be deep-rooted, dredging chemicals from Jupiter’s interior, which might clarify why it has been steady for so long. The new pictures, coupled with Juno’s microwave and gravity observations, could disclose, for the first time, how far down that spot really goes.
5. Why is it red?
In spite of decades of planetary exploration, we still don’t know how the gases in Jupiter’s cloud tops react to make the red coloring we see in the spot. For that matter, it’s not continuously red: sometimes it’ll fade to orange, or take on hues of salmon pink or rusty brown. These colors may be linked to sunlight breaking down the chemical bonds of materials dredged up by the upsurge in the storm. These chemically changed species might have compounds of sulphur, phosphorus and hydrocarbons, which could lead to the red colors. Juno’s suite of instruments, combined with these remarkable new pictures, might shed light on this mystery.
At the cloud tops, the Great Red Spot is cold since air is rising within the vortex, growing and cooling down. This cooling causes gases to condense to ices, producing a thick cloud cover high over the storm. Yet thermal infrared imaging discloses that the Great Red Spot has a warm heart. This warm area accords with the deepest red cloud colors shown in the recent images, and perhaps a stagnation of the winds. Is this the core of the vortex, telling us what the storm looks like at depth? If so, what are the temperatures like well below the clouds? Again, Juno’s microwave observations may well reveal the answer.
