we are used to it seeing Neptune in shades of deep blue, but in the most recent images from the James Webb Space Telescope, the ice giant shines in a silvery light, surrounded by pale cobweb rings and faint dust lanes.
No spacecraft has visited Neptune since Voyager 2 swooped by in 1989 as it left the Solar System, but from a vantage point 2.7 billion miles away, Webb shows us Neptune in a whole new light: near-infrared, specifically. . And that’s why Neptune looks so different from its usual blue color in Webb’s latest images.
In the wavelengths of light that our eyes can see, the methane gas in Neptune’s atmosphere appears blue. But at infrared wavelengths, methane gas absorbs so much light that it looks dark gray (or the infrared equivalent of dark gray; Webb’s image-processing team translated infrared wavelengths into visible colors to produce these images). . The frozen methane ice particles in Neptune’s highest clouds nonetheless reflect most of the sunlight that hits them, so they appear dazzlingly bright to Webb’s instruments.
Those high-altitude clouds could help planetary scientists discover more details about Neptune’s stormy and windy weather. A faint, thin line of brightness around the ice giant’s equator, for example, could be a telltale sign of the global circulation pattern that drives the planet’s climate. As gases in Neptune’s atmosphere flow toward the equator, they heat up, making them appear brighter in infrared images.
Neptune does have rings, though they are so faint that astronomers often don’t see them. Its dust-covered ice particles may be all that remains of an ancient moon, which orbited so close to Neptune that the force of the planet’s gravity tore it apart. Webb’s first image of Neptune reveals some rings astronomers have never seen before, and an updated look at others that haven’t been photographed since Voyager 2’s flyby.
Webb also captured seven of Neptune’s 14 moons in his images, including the biggest and strangest: Triton. It orbits Neptune backwards, possibly because it was once a dwarf planet like Pluto and Sedna that got caught in Neptune’s gravity and pulled it into what astronomers call a retrograde orbit. Triton shimmers in Webb’s images, with huge diffraction spikes as if it were a nearby star instead of a moon; That’s because its surface layer of nitrogen ice reflects most of the sunlight that hits it, making Triton look even brighter than the planet that’s holding it hostage.
Over the next several months, Webb will observe Neptune and its moons in more detail, which may shed even more light on the system’s checkered history.