Auroras captured in Neptune for the first time, thanks to the webb telescope

For the first time, the James Webb special telescope has captured Neptune’s auroral activity, the piece that was missing from the puzzle to detect auroras on the giant planets of the solar system.

The auroras occur when energy particles, often from the sun, are trapped in the magnetic field of a planet and finally impact the upper atmosphere. The energy released during these collisions creates the characteristic brightness.

In the past, astronomers have observed promising signs of auroral activity in Neptune, for example, in the NASA Voyager 2 overflow in 1989. However, obtaining images and the confirmation of auroras in Neptune has been a mystery to astronomers for a long time, despite successful detections in Jupiter, Saturn and Uranus. Neptune was the piece that was missing from the puzzle to detect auroras on the giant planets of our solar system.

Real images

“It turns out that obtaining real images of auroral activity in Neptune It was only possible thanks to the sensitivity of the webb in the near infrared“said the main author, Henrik Melin, from the University of Northumbria, who directed the research while studying at Leicester University. It was impressive not only to see the auroras, but also the detail and clarity of his firm. He said.

The data were obtained in June 2023 using the webb’s nearby infrared spectrograph. In addition to the image of the planet, astronomers obtained a spectrum to characterize the composition and measure the temperature of the upper atmosphere of the planet (the ionosphere). For the first time, they found an extremely prominent emission line that indicates the presence of the trihydrogen cation (H3), which can be formed in the auroras. In the images of Neptune of the Webb, The bright aurora appears as spots represented in cyan.

“The H3+ has been a clear indicator of auroral activity in all gaseous giants -Jupiter, Saturn and Uranus -, and we hoped to observe the same in Neptune when investigating the planet for years with the best available terrestrial facilities,” Heidi Hammel, of the Association of University for Research in Astronomy (Aura), interdisciplinary scientist, an interdisciplinary scientist, Webb and leader of the Guaranteed Time Observation program for the Solar System, where the data was obtained. “Only with a team like the Webb we have finally obtained that confirmation.”

Different from Jupiter and Saturn

The Auroral activity observed in Neptune is also remarkably different to which we are used to seeing here on earth, or even in Jupiter or Saturn. Instead of limiting themselves to the northern and southern poles of the planet, Neptune’s auroras are located in the geographical average latitudes of the planet.

This is due to the strange nature of Neptune’s magnetic field, originally discovered by the Voyager 2 in 1989, which presents an inclination of 47 degrees with respect to the axis of rotation of the planet. Since auroral activity is concentrated where magnetic fields converge in the planet’s atmosphere, Neptune’s auroras are far from their rotation poles.

The detection of Neptune auroras will help understand how its magnetic field interacts with the particles that emanate from the sun towards the confines of our solar system, which represents a totally new window in the atmospheric science of ice giants.

Cooling in hundreds of degrees

From the observations of the Webb Telescope, the team also measured the temperature of the upper part of the Neptune atmosphere for the first time from the flying of the Voyager 2. The results give a clue why Neptune auroras remained hidden from astronomers for so long.

“I was stunned: Neptune’s upper atmosphere has cooled several hundred degrees,” Melin said. In fact, the temperature in 2023 was a little more than half than in 1989.

Over the years, astronomers have predicted the intensity of Neptune’s auroras based on the temperature recorded by Voyager 2. A substantially colder temperature would result in much more faint auroras. This low temperature is probably the reason why Neptune’s auroras have remained unnoticed for so long. The drastic cooling also suggests that this region of the atmosphere can change considerably despite the fact that the planet is 30 times further from the sun than the Earth.