Jupiter’s clouds hide huge pillars of ammonia gasses

When NASA’s Galileo mission sent a probe down into Jupiter’s clouds, it sent back an unusual find: The probe seemed to be plummeting into a thick stew of slow-moving ammonia, in contrast to the more varied upper atmosphere.

Now, a Berkeley-led team may have unraveled the mystery. The researchers think that Galileo plunged into a “storm” of ammonia just below the surface of the upper atmosphere, happening onto just the right spot to descend into one of the “hot spots” faintly visible from the surface.

Imke de Pater, said that the Galileo probe showed the columns to be made of four to five times the amount of ammonia seen in the “solar abundance.” That’s a term for the spectrum emanated from the Sun displaying the elements its fusing. She’s quick to point out that in the Sun, similar spectral lines radiate as nitrogen, but nitrogen bonds with hydrogen in the much cooler atmosphere of Jupiter to become ammonia.

But that’s not the case for Jupiter’s violent surface gasses, in which ammonia is much more dispersed over the visible upper atmosphere, but more compressed down below. There was some sort of disharmony there. After mapping the entire surface of Jupiter, the team was able to find small oval shapes that corresponded to high concentrations of ammonia.

These columns reach right up to the highest cloud layers, then disperse the ammonia at these lower pressure levels.

“That explains why, on average, Jupiter’s atmosphere seems to be depleted in ammonia gas while in some places it’s quite abundant,” de Pater said.

Still, she said, they haven’t yet identified a cause. Something deep in Jupiter’s clouds is causing the convection effect, but the lower levels of Jupiter’s atmosphere are, of yet, poorly understood. It’s also not well known if similar structures appear on the other gas giants, which may also have ammonia left over from the solar system’s formation.

The upcoming Juno mission may be able to shed some light, de Pater said, through an instrument meant to measure water abundance. The water line and ammonia line are located near each other on the electromagnetic spectrum. But the two competing signals also may dilute some of the results.

“To disentangle these effects will be pretty hard, but it’s the only experiment that has a chance of doing it,” she said.

To find out what’s really going on, it’d take another Galileo-style atmospheric probe. But even that presents more than a few challenges.

“You need to get it down in the right area. That is really difficult,” de Pater said. “The Galileo probe, just by chance, went down into a hot spot.”

In the meantime, we’ll just have to contend with a mystery in Jupiter’s atmosphere — and the scant breadcrumb trail to find more answers.