Telescope captures sight of bright auroras, but these aren’t on Earth

WASHINGTON – NASA’s James Webb Space Telescope has captured the first-ever images of aurora activity on Neptune, unveiling new secrets about the distant planet.

The space agency explained that, in the past, scientists could only speculate about such activity on the solar system's eighth planet, but glowing splotches observed by Webb in 2023 have led to groundbreaking theories. 

"Turns out, actually imaging the auroral activity on Neptune was only possible with Webb’s near-infrared sensitivity," Henrik Melin, an associate professor at Northumbria University, said in a statement. "It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me."

Experts who examined the data found splotches in the imagery of Neptune, along with a signature of specially charged molecules, which indicated the existence of auroral activity. This phenomenon has also been observed on other gas giants.

Auroras occur when particles from the Sun enter a planet’s magnetic field and collide with the upper atmosphere, releasing energy in the form of light. While the aurora phenomenon is well documented on Earth, it has also been observed on Jupiter, Saturn, Uranus, Mars, and Venus - but with some key differences.

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NASA pointed out that unlike Earth’s auroras, which are typically confined to the planet’s northern and southern poles, events on Neptune are located around the planet’s mid-latitudes. 

The agency did not specify how frequently these auroras occur, but on Earth, the Aurora Borealis and Aurora Australis occur nearly every evening.

Scientists say the discovery is not only visually stunning but will also lead to critical studies about Neptune’s composition.

In addition to capturing the auroral images, Webb’s instruments have allowed astronomers to measure the temperature of Neptune’s atmosphere. 

Data revealed that the planet’s upper layers have significantly cooled since observations made by the Voyager 2 spacecraft.

On August 25, 1989, Voyager 2 passed just 3,000 miles above Neptune, gathering the first-ever close-up observations, which were transmitted back to Earth.

By comparing data collected over 30 years ago, researchers now believe Neptune’s atmospheric temperature has dropped by several hundred degrees, explaining why the auroras were previously difficult to detect.

"I was astonished — Neptune’s upper atmosphere has cooled by several hundred degrees," Melin said. "In fact, the temperature in 2023 was just over half of that in 1989."

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Scientists have yet to explain why the planet is believed to have cooled so significantly, with potential contributing factors ranging from the Sun’s cycles to local weather patterns.

With the new findings, astronomers hope to study Neptune’s changes over the course of a full solar cycle, which will provide valuable insights into how the Sun affects the region nearly 3 billion miles away.

"As we look ahead and dream of future missions to Uranus and Neptune, we now know how important it will be to have instruments tuned to the wavelengths of infrared light to continue studying the auroras," said Leigh Fletcher, a professor of planetary science at Leicester University. "This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets."