When you think of ringed planets, Saturn probably comes to mind, but it’s not the only one in the solar system. Neptune has faint rings as well, but they’re difficult to observe from so far away. NASA’s James Webb Space Telescope (JWST) recently turned its attention to the eighth planet, producing the clearest image of the ice giant’s rings since Voyager 2 flew past decades ago.
Neptune is the most distant planet in the solar system, not including dwarf planets like Pluto. Voyager 2 is the only spacecraft to ever visit this world — it was the last stop on the “Grand Tour” before the probe headed toward the edge of the solar system. Some of Neptune’s rings are visible with other observatories, but even Hubble couldn’t produce an image like Webb, which has more than six times the light collecting area.
Neptune is an ice giant based on the chemical makeup of its interior. Other gas giants like Jupiter and Saturn have higher concentrations of helium and hydrogen. Neptune, on the other hand, is high in heavier elements with hints of gaseous methane — that’s what makes it blue in the visual spectrum. The JWST operates in the near-infrared range from 0.6 to 5 microns with its NIRCam instrument, so Neptune doesn’t have its trademark blue color in the new image. Instead, parts of the globe are dark while others are quite luminous.
This is a new view of the rings. “It has been three decades since we last saw these faint, dusty rings, and this is the first time we’ve seen them in the infrared,” says Neptune expert and Webb scientist Heidi Hammel. All three of them are composed of ice particles coated with silicates or carbon, which makes them reddish in the visual spectrum. Usually, the rings are too faint compared to the planet to capture, but Webb’s super-high resolution makes it possible. Webb also spotted seven of Neptune’s 14 moons in this image.
According to NASA, methane absorbs red and infrared light very strongly, but areas with high-altitude clouds behave a bit differently. These prominent methane-ice clouds cause the bright streaks and spots in the image because they reflect sunlight before it can be absorbed by gaseous methane at lower altitudes. You can even see the faint band around the equator that is a signature of Neptune’s global atmospheric circulation. Gasses descend to lower altitudes and warm in that region, causing a slight glow in the infrared.
The Webb Telescope took 20 years to develop and build, but it finally launched late last year. After a few months of testing and calibration, it has started doing amazing science. And it’s not stopping anytime soon. Thanks to a perfect launch, Webb has enough fuel to continue operating for up to 20 years.