Webb captures Jupiter's surprisingly active Northern Lights
The auroras surrounding the north pole of our solar system's largest planet had some surprises in store when astronomers aimed JWST at them.
A fresh look at Jupiter's powerful auroras with the James Webb Space Telescope has revealed never-before-seen details, and has uncovered a strange mystery for researchers to solve.
On Christmas Day in 2023, a team of astronomers aimed the sensitive Webb Telescope at the largest planet in our solar system. Although this had been done before, they had a very specific target in mind — the intense auroras that surround the immense planet's magnetic north pole.
While these Jovian Northern Lights had been imaged in the past, using the Hubble Space Telescope, Webb provided them with an unprecedented view, capturing the details of this phenomenon like never before.
Jupiter’s auroras (left) captured by the James Webb Space Telescope’s NIRCam (Near-Infrared Camera) on Dec. 25, 2023. The image on the right shows the planet Jupiter to indicate the location of the observed auroras, which was originally published in 2023. (NASA, ESA, CSA, STScI, Ricardo Hueso (UPV), Imke de Pater (UC Berkeley), Thierry Fouchet (Observatory of Paris), Leigh Fletcher (University of Leicester), Michael H. Wong (UC Berkeley), Joseph DePasquale (STScI), Jonathan Nichols (University of Leicester), Mahdi Zamani (ESA/Webb))
"What a Christmas present it was — it just blew me away!" Jonathan Nichols, the lead researcher of this study from the University of Leicester, said in a NASA press release.
Auroras on Earth — the Northern Lights and Southern Lights — occur as high-energy particles from the Sun stream past the planet, either flowing on the solar wind or from massive eruptions of solar matter, known as coronal mass ejections (CMEs), sweeping by us.
These particles are captured by our planet's geomagnetic field and funnelled down into the upper atmospehre. There, they collide with atoms and molecules of oxygen and nitrogen in the air, passing on their energy. The energized oxygen and nitrogen then release that energy as coloured flashes of light — greens and reds from oxygen, and mostly blue from nitrogen.
The Northern Lights, spotted near Guelph, ON, on September 16, 2024. (Stormhunter Mark Robinson)
This same process occurs on Jupiter, but with an additional source of high energy charged particles.
While the planet's intense magnetic field captures particles from the solar wind and CMEs, it also picks up ionized particles from the innermost of its four largest moons.
Io is the most volcanically active object in the solar system. Hundreds of volcanoes dot its surface, which are powered by the tidal stretching and squeezing induced by the gravitational 'tug-of-war' the moon endures as it orbits the planet and periodically passes by its neighbours, Europa and Ganymede.
Io, imaged by NASA's Juno spacecraft during its 57th pass around Jupiter. The combinations of blemished and smooth terrain on the surface is due to nearly constant volcanic activity. (NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill)
Jupiter's magnetic field acts like a particle accelerator, driving this combination of solar and volcanic ions down into the planet's upper atmosphere so they hit the atoms and molecules there at tremendous speeds. As a result, Jupiter's auroras glow extremely brightly.
Since the process of producing auroras also generates heat, aka infrared light, Jovian auroras show up very brightly to Webb, which is specifically designed to capture that part of the spectrum of light. This allowed the researchers to get a very detailed view of the auroras, and spot how they changed with time.
What they saw over the course of their observations surprised them.
"We wanted to see how quickly the auroras change, expecting them to fade in and out ponderously, perhaps over a quarter of an hour or so," Nichols explained. "Instead, we observed the whole auroral region fizzing and popping with light, sometimes varying by the second."
Three different views of Jupiter's auroras are shown here from Dec. 25, 2023, superimposed on an earlier JWST image of the planet. (NASA, ESA, CSA, STScI, Ricardo Hueso (UPV), Imke de Pater (UC Berkeley), Thierry Fouchet (Observatory of Paris), Leigh Fletcher (University of Leicester), Michael H. Wong (UC Berkeley), Joseph DePasquale (STScI), Jonathan Nichols (University of Leicester), Mahdi Zamani (ESA/Webb))
Jupiter's auroras also produce a rare type of hydrogen known as the trihydrogen cation. Normal hydrogen gas is composed of two hydrogen atoms, thus there are two protons in the nucleus, which are surrounded by two electrons. In a trihydrogen cation, there are three protons surrounded by two electrons, which causes it to be positively charged.
It was this very specific molecule that Nichols and his team were able to focus Webb onto, to gather the data for their study.
According to NASA, detecting the emissions from these trihydrogen cations will help scientists understand how the upper atmosphere of Jupiter heats and cools.
A mystery revealed
There was one odd thing that Nichols' team noticed in their observations.
Auroras show up in various colours across the spectrum of visible light, such as green, red, and blue. However, when we use telescopes to see auroras on Jupiter, we only see them in infrared and ultraviolet wavelengths. In this case, JWST handled the infrared observations, while another telescope provided the ultraviolet view.
"What made these observations even more special is that we also took pictures simultaneously in the ultraviolet with NASA’s Hubble Space Telescope," Nichols explained.
Comparing the images from opposite ends of the spectrum is where a mystery popped up. The assumption was that the brightest regions in both UV and IR light should match up. However, they didn't.
"Bizarrely, the brightest light observed by Webb had no real counterpart in Hubble's pictures," Nichols said. "This has left us scratching our heads. In order to cause the combination of brightness seen by both Webb and Hubble, we need to have a combination of high quantities of very low-energy particles hitting the atmosphere, which was previously thought to be impossible. We still don't understand how this happens."
The difference might be due to the abundance of particles from the Sun versus the abundance of volcanic particles from Io. Or, there may be something else going on here that they haven't accounted for.
According to NASA, the research team plans on delving deeper into their comparison between the Webb and Hubble data they collected. They also plan on making further observations with Webb, which can be compared with data from the Juno spacecraft currently orbiting Jupiter.