Everyone knows the majestic rings of Saturn. But it is not the only planet in our cosmic neighborhood that has them: Jupiter, Uranus y Neptune they also have formations of dust and gas floating around them. Now the James Webb Space Telescope has set its sights on this last world, revealing the clearest snapshots in 30 years and a whole new perspective.
Since the NASA spacecraft Voyager 2 When flying over the icy giant in 1989, its imposing rings had not been seen in the same way, in which now even the faintest dust bands can be seen. “It’s been three decades since we last saw these faint, dusty rings, and this is the first time we’ve seen them in the infrared,” he says. Heidi Hammel, an expert on Neptune systems and an interdisciplinary scientist on the Webb Telescope team. “Webb’s extremely stable and precise image quality makes it possible to detect these very faint rings that are so close to Neptune.”
Located 30 times farther from the Sun than Earth, Neptune orbits in the remote and dark region of the outer solar system. At that extreme distance, the Sun is so small and faint that noon on Neptune is similar to a dimly lit twilight on Earth.
What do we see in Webb’s image of the ice giant Neptune? The space telescope imaged seven of Neptune’s 14 known moons: Galatea, Naiad, Thalassa, Despina, Proteus, Larissa, and Triton. Neptune’s large and unusual moon Triton stands out in this portrait taken by Webb as a very bright point of light showing the characteristic diffraction spikes seen in many of Webb’s images.
This planet is characterized as an ice giant due to the chemical composition of its interior. Compared to the gas giants Jupiter and Saturn, Neptune is much richer in elements heavier than hydrogen and helium. This is readily apparent in its blue appearance in Hubble Space Telescope images at visible wavelengths, caused by small amounts of gaseous methane.
methane ice clouds
Webb’s near-infrared camera (NIRCam, for its acronym in English) produces images of objects in the near-infrared range between 0.6 and 5 microns, so Neptune does not appear blue through Webb’s instruments. In fact, methane gas absorbs red and infrared light so strongly that the planet is quite dark at these near-infrared wavelengths, except where there are high-altitude clouds. Such methane ice clouds stand out as bright streaks and spots, reflecting sunlight before it is absorbed by methane gas. Images from other observatories, including the Hubble Space Telescope and the WM Keck Observatory, have recorded these rapidly evolving cloud features over the years.
More subtly, a thin line of brightness encircling the planet’s equator could be a visual cue for the global atmospheric circulation that feeds the winds and storms of Neptune. The atmosphere sinks and heats up at the equator, and therefore shines brighter in infrared wavelengths than the cooler surrounding gases.
The mysteries of the image
Neptune’s 164-year orbit means that its north pole, at the top of this image, is out of sight for astronomers, but the Webb images suggest an intriguing glow in that area. A previously known vortex at the south pole is evident in Webb’s view, but for the first time Webb has revealed a continuous band of high-latitude clouds surrounding it.
Webb also caught seven of the 14 known moons of Neptune. A very bright point of light stands out in this Webb portrait of Neptune, showing the characteristic diffraction spikes seen in many of Webb’s images, but this is not a star. Rather, this is Neptune’s large and unusual moon, Triton.
Covered in an icy sheen of condensed nitrogen, Triton reflects an average of 70 percent of the sunlight that hits it. It outshines Neptune in this image because the planet’s atmosphere is obscured by methane absorption at these near-infrared wavelengths. Triton orbits Neptune in an unusual retrograde orbit, leading astronomers to speculate that this moon was originally a Kuiper Belt Object that was gravitationally captured by Neptune. Additional studies with Webb of both Triton and Neptune are scheduled for next year.
