Jupiter’s Great Red Spot (GRS) is a ten-thousand-mile-wide tempest that has been roiling in the planet’s atmosphere for centuries, but new data from a pair of studies unveiled at a NASA press conference has shown that the GRS and its feeder currents extend deeper into the gas giant than we previously knew.
At the press conference, two teams of astronomers — Scott Bolton and colleagues as well as Marzia Parisi and colleagues, reported that they used microwave radiometry and gravity measurements, respectively, to characterize Jupiter’s atmospheric vortices, including the GRS. Both teams relied on the space probe Juno — Bolton’s group used Juno’s onboard microwave radiometer to characterize the vertical structure of the GRS (as well as two other storms) and found that they extend well below the planet’s cloud layer.
In terms of its footprint, the GRS is more than capable of swallowing the Earth entire. It is smaller now than it used to be, and faded, but it’s still awful. Conservatively, the maelstrom extends at least 120 miles into the planet, but it could be as much as 300 miles deep — it could go even further, but that’s as deep as Juno’s radiometer can “see” it. “The Great Red Spot is as deep within Jupiter as the International Space Station is high above our heads,” said Parisi, a research scientist at the JPL. But compared to the zonal jets that feed the storm, the GRS is just a surface eddy. Those zonal currents cut almost two thousand miles deep into Jupiter’s lightless depths.
Gigantic, stable, long-lived storms are a recurring theme on Jupiter, and with Juno we finally have a chance to look below the tops of the clouds. The planet is mostly hydrogen by mass, and it has no true surface; instead, we think it makes a gradual transition through thicker and denser clouds into an opaque, ammoniac slush with perhaps the density of water. At a thousand kilometers below the cloudtops, we observe such extreme cold that the distinction between liquid and gas begins to blur. Hydrogen becomes a transparent supercritical fluid, free of surface tension and capable of wafting through solids like a gas instead of seeping like a liquid. But there’s nothing solid on Jupiter. Wind belts carve unobstructed paths through the gas giant’s atmosphere. These stable circulations produce resident storms arranged at the planet’s poles with geometric precision, in a perfect octagon at the north pole, and a perfect hexagon at the south. It is thought that they produce raindrops of helium, neon, and perhaps even diamond, which fall into a bottomless ocean of liquid hydrogen that never becomes solid, even at the planet’s core.
As Juno continues to investigate the planet, we’ll continue to receive updates. Juno is orbiting Jupiter in order to learn about the planet’s origin and evolution, to study its core and magnetic field, and to obsessively photograph everything it possibly can. More data is certain to come, as NASA has extended Juno’s mission until at least 2025.
“Jupiter’s beauty is not just skin deep,” says Bolton, principal investigator of the Juno mission. “And we are seeing, for the first time, the atmosphere in three dimensions.”
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