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- The Webb space telescope has finally caught auroras on Neptune.<\/strong> Neptune lies in the frigid, dark, vast frontier of the outer edges of our solar system about 3 billion miles away from the sun.<\/li>\n
- Observatories like NASA\u2019s Hubble Space Telescope have tracked the planet\u2019s changing weather.<\/strong> Hubble even discovered a new moon orbiting the planet in 2013.<\/li>\n
- In many images, the planet appears as a bluish orb,<\/strong> sometimes with disappearing and reappearing dark spots. NASA\u2019s James Webb Space Telescope has now revealed a different appearance: a bright auroral glow from this ice giant.<\/li>\n<\/ul>\n
NASA\u2019s Webb Space Telescope published this original story on March 26, 2025. Edits by EarthSky.<\/p>\n
First views of auroras on Neptune<\/h3>\n
On March 26, 2025, NASA shared the first image of bright auroral activity on Neptune, thanks to the Webb space telescope. Auroras occur when energetic particles, often originating from the sun, become trapped in a planet\u2019s magnetic field. They eventually strike a planet\u2019s upper atmosphere. The energy released during these collisions creates the signature glow. <\/p>\n
In the past, astronomers have seen tantalizing hints<\/em> of auroral activity on Neptune, for example, in the flyby of NASA\u2019s Voyager 2 in 1989. However, imaging and confirming the auroras on Neptune has long evaded astronomers. That\u2019s despite successful detections on Jupiter, Saturn and Uranus. Neptune was the missing piece of the puzzle when it came to detecting auroras on the giant planets of our solar system. <\/p>\n
Lead author Henrik Melin of Northumbria University in the U.K. conducted the research while at the University of Leicester. Melin said:<\/p>\n
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Turns out, actually imaging the auroral activity on Neptune was only possible with Webb\u2019s near-infrared sensitivity. It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me.<\/p>\n<\/blockquote>\n
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Cyan splotches represent auroras<\/h3>\n
The scientists obtained the data in June 2023 using Webb\u2019s Near-Infrared Spectrograph. In addition to the image of the planet, astronomers obtained a spectrum to characterize the composition and measure the temperature of the planet\u2019s upper atmosphere (the ionosphere). For the first time, they found an extremely prominent emission line. This emission line signified the presence of the trihydrogen cation (H3+). And auroras can create these ions. In the Webb images of Neptune, the glowing auroras appear as splotches in cyan.<\/p>\n
Heidi Hammel of the Association of Universities for Research in Astronomy, Webb interdisciplinary scientist and leader of the Guaranteed Time Observation program which obtained the data were obtained, said:<\/p>\n
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H3+ has a been a clear signifier on all the gas giants \u2013 Jupiter, Saturn and Uranus \u2013 of auroral activity, and we expected to see the same on Neptune as we investigated the planet over the years with the best ground-based facilities available. Only with a machine like Webb have we finally gotten that confirmation.<\/p>\n<\/blockquote>\n
Auroras on Neptune are different<\/h3>\n
The auroral activity seen on Neptune is also noticeably different from what we are accustomed to seeing here on Earth, or even Jupiter or Saturn. Instead of being confined to the planet\u2019s northern and southern poles, Neptune\u2019s auroras are at the planet\u2019s geographic mid-latitudes. So picture where South America is located on Earth. <\/p>\n
Neptune\u2019s magnetic field is responsible for this, which Voyager 2 originally discovered in 1989. It tilts by 47 degrees from the planet\u2019s rotation axis. Since auroral activity is based where the magnetic fields converge into the planet\u2019s atmosphere, Neptune\u2019s auroras are far from its rotational poles.<\/p>\n
The ground-breaking detection of Neptune\u2019s auroras will help us understand how Neptune\u2019s magnetic field interacts with particles that stream out from the sun to the distant reaches of our solar system. It is a totally new window in ice giant atmospheric science.<\/p>\n
From the Webb observations, the team also measured the temperature of the top of Neptune\u2019s atmosphere for the first time since Voyager 2\u2019s flyby. The results hint at why Neptune\u2019s auroras remained hidden from astronomers for so long. Melin said:<\/p>\n
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I was astonished; Neptune\u2019s upper atmosphere has cooled by several hundreds of degrees. In fact, the temperature in 2023 was just over half of that in 1989.<\/p>\n<\/blockquote>\n
![\"A](\"https:\/\/earthsky.org\/upl\/2025\/03\/Henrik-Melin-Northumbria-Univnersity-e1742992557744.jpg\")
Henrik Melin of Northumbria University is the lead author of the new study. He conducted the research while at the University of Leicester. Image via Northumbria University.<\/figcaption><\/figure>\n A cooling planet<\/h3>\n
Through the years, astronomers have predicted the intensity of Neptune\u2019s auroras based on the temperature recorded by Voyager 2. A substantially colder temperature would result in much fainter auroras. This cold temperature is likely the reason that Neptune\u2019s auroras have remained undetected for so long. The dramatic cooling also suggests that this region of the atmosphere can change greatly even though the planet sits over 30 times farther from the sun compared to Earth.<\/p>\n
Equipped with these new findings, astronomers now hope to study Neptune with Webb over a full solar cycle. The sun\u2019s magnetic field drives this 11-year period of activity. Results could provide insights into the origin of Neptune\u2019s bizarre magnetic field. And it might even explain why it\u2019s so tilted.<\/p>\n
Leigh Fletcher of the University of Leicester in the U.K., co-author on the paper, said:<\/p>\n
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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 to study the auroras. This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets.<\/p>\n<\/blockquote>\n
Bottom line: For the first time, the Webb space telescope has revealed auroras on Neptune. See images and read more about it here.<\/p>\n
Source: Discovery of H3+ and infrared aurorae at Neptune with JWST<\/p>\n
Via Webb Space Telescope<\/p>\n
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\n - Observatories like NASA\u2019s Hubble Space Telescope have tracked the planet\u2019s changing weather.<\/strong> Hubble even discovered a new moon orbiting the planet in 2013.<\/li>\n