NASA's First-Ever Image Of Neptune's Glowing Auroras Is A Stunner
It only took some 417 years since the invention (if going by patent filings) of the telescope to finally see Neptune's auroras, and it's thanks to NASA's James Webb Space Telescope, or JWST (the same telescope that provided a crystal clear view of Neptune's rings in 2022). Webb is much more powerful than the handheld refracting telescope patented by Hans Lipperhey, a German-Dutch eyeglass maker, way back in 1608, though that wasn't the only factor in capturing Neptune's auroral glow for the first time ever.
According to NASA, astronomers have come close to spying Neptune's auroras before. One of those times came in 1989 when NASA's Voyager 2 probe performed a flyby of the planet that sits around 2.87 billion miles away from Earth. That remains the only time a spacecraft has visited Neptune, though NASA's Hubble telescope has continually tracked the planet's weather changes. It also discovered a new moon orbiting Neptune as recently as 2013.
Therein lies one of the challenges leading up to this historic moment. Auroras are much fainter in frigid temperatures, making them more difficult to see. The average temperature of Neptune's atmosphere has fallen in recent decades, to -117C (-179F). It's even colder if looking at Neptune's whole surface, with temps averaging -200C (-330F). And the planet's troposphere, or weather layer, averages a brutally chilly -223C (-370F). According to NASA, the cold temperature on Neptune is probably the reason why the auroras have remained mostly hidden from view all this time.
Webb's response? Challenge accepted.
"Turns out, actually imaging the auroral activity on Neptune was only possible with Webb’s near-infrared sensitivity," said lead author Henrik Melin of Northumbria University, who conducted the research while at the University of Leicester. "It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me."
Webb's Near-Infrared Spectrograph (NIRSpec) obtained the auroral data in June 2023. This data allowed astronomers to analyze the planet's upper atmosphere (or the ionosphere) where they found "an extremely prominent emission line signifying the presence of the trihydrogen cation (H3+)." This is notable because it can be created in auroras, which appear as cyan-colored splotches.
"H3+ has a been a clear signifier on all the gas giants—Jupiter, Saturn, and Uranus—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," explained Heidi Hammel of the Association of Universities for Research in Astronomy, Webb interdisciplinary scientist and leader of the Guaranteed Time Observation program in which the data were obtained. "Only with a machine like Webb have we finally gotten that confirmation."
It's an incredible feat when looking at all of the science involved, and because of it, we get our first-ever look at Neptune's auroras. Furthermore, astronomers are hopeful that the new findings will enable them to study the icy giant's full solar cycle over an 11-year period of activity, which in turn could finally detail the origin story of Neptune's odd magnetic field, as well as answer why it's so tilted.
