An image of Jupiter taken at different wavelengths by ALMA shows that the planet’s zones (bright) are warmer and belts (darker) cooler. Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello
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An image of Jupiter taken at different wavelengths by ALMA shows that the planet’s zones (bright) are warmer and belts (darker) cooler. Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello

As a Jupiter storm erupts, ALMA peers below its clouds

Contributed by
Aug 27, 2019

I do love pictures of Jupiter. Besides the awesome gorgeousity of the planet, there is something even cooler about seeing high-resolution images of an object I've seen myself through the eyepiece literally hundreds of times. Details just barely hinted at by eye become huge vistas from bigger 'scopes, and giant storms normally dwindled by vast distance suddenly pop into existence.

And then there are the views of this giant world that reveal stuff that is bizarrely unfamiliar, transforming it from a comfortable, reliable target into an alien landscape that reminds us that no matter how familiar we are with it, it's still another planet.

These situations become a lot easier when you view the Big Guy using a telescope that sees light far, far outside of the human eye's range. Like, say, ALMA:

An image of Jupiter taken at different wavelengths by ALMA shows that the planet’s zones (bright) are warmer and belts (darker) cooler. Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello

An image of Jupiter taken at different wavelengths by ALMA shows that the planet’s zones (bright) are warmer and belts (darker) cooler. Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello

Oh yeah. That's cool.

ALMA is the Atacama Large Millimeter/submillimeter Array, which looks at wavelengths of light that are so long they're just on this side of what we call radio, and far longer than visible or even infrared light.

Jupiter emits this sort of light, but not evenly. You can see broad stripes across the planet; these are the belts and zones. They're wind patterns that flow in opposite direction across Jupiter, and represent the cloud tops. Belts have cloud tops slightly higher in the atmosphere, and zones lower. Normally you'd see storms dotting the stripes, but in this image Jupiter's rotation has smeared out the details.

Now, in visible light, zones appear brighter because they have more ammonia in them, which is bright and reflective. Belts are darker. But, in the ALMA image that's reversed! Zones are cooler, so they appear darker, and belts are warmer, so they appear brighter.

You can compare them yourself:

ALMA image of Jupiter (top) shows many of the same features as a Hubble image (bottom), including the Great Red Spot, and a region near it where a plume from deep inside the planet’s atmosphere erupted in January 2017. ALMA (ESO/NAOJ/NRAO), I. de Pater et

ALMA image of Jupiter (top) shows many of the same features as a Hubble image (bottom), including the Great Red Spot, and a region near it where a plume from deep inside the planet’s atmosphere erupted in January 2017. ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA/Hubble

This shows a more detailed ALMA image above a Hubble image in visible light, "unwrapped" as it were, taking the spherical planet and stretching it out flat. In both you can see the Great Red Spot (warm around the edges and cooler in the middle in the ALMA image) and the zones and belts.

Not obvious in these images is another interesting and useful thing. Ammonia (NH3) in Jupiter's atmosphere is really good at absorbing come wavelengths ALMA is sensitive to. So too are ammonium hydrosulfide (NH4SH), and even water. These molecules exist at different depths in Jupiter's atmosphere, and absorb light at slightly different wavelengths, so by adjusting how ALMA observes, the astronomers could also make 3D maps of Jupiter's atmosphere.

Anatomy of a Jupiter storm. The details are obviously complex, but feature similarities to Earth’s storms, such as rising warm air and sinking moist cooler air. Credit: Adapted from illustration by Leigh Fletcher, University of Leicester (Via UC Berkeley)

Anatomy of a Jupiter storm. The details are obviously complex, but feature similarities to Earth’s storms, such as rising warm air and sinking moist cooler air. Credit: Adapted from illustration by Leigh Fletcher, University of Leicester (Via UC Berkeley)

By doing this they could see from the ammonia cloud deck at the tops of the clouds (where the atmospheric pressure is similar to that at sea level here on Earth) down to about 8- kilometers below that, where pressures are several times higher. That's useful! As it happens, these observations were made just after amateur astronomers discovered a new storm in Jupiter's Southern Equatorial Belt (the same belt the Red Spot sits in) in January 2017. These are caused by plumes of material rising up from Jupiter's interior, which then bubble up to the cloud tops where we can see them.

That means the astronomers could use ALMA to trace these gases farther down and see what they're doing. Once they erupt, these storms get whipped around by the fierce and turbulent winds, getting stretched out to form lovely rippling shapes. Seeing them in 3D means better understanding what causes them, how they change over time, and what they're made of.

These observations were made along with other observatories like Keck, the Very Large Telescope, Subaru, and Gemini (in the infrared), the Very Large Array (radio), and Hubble (visible) to get as much multi-wavelength information on Jupiter as possible. Each sees different aspects of the atmosphere, giving astronomers a huge amount of data they can use to probe it. In fact, these observations were all timed to be near the time when the Juno spacecraft was in the part of its orbit when it dives closest to Jupiter's cloud tops, so that they can be used to support those observations and give them context.

Jupiter is a vast, sprawling planet, huge beyond our puny brains to truly grasp and our senses' ability to perceive all at once. But that's why we observe it with all these different telescopes! Not only that, but a few months before these observations, a system of four storms erupted in the North Temperate Belt, changing its color from its normal white to orange. They had already faded by the time of all these observations, but it shows how important it is to keep our eyes on Jupiter… no matter what kind of light those eyes see.

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