The last time astronomers had such a clear view of the farthest planet from the sun was when Nasa’s Voyager 2 became the first and only spacecraft to fly past the ice giant for just a few hours in 1989. Now Webb’s unprecedented infrared imaging capability has provided a new look at Neptune’s atmosphere, said Mark McCaughrean, senior adviser for science and exploration at the European Space Agency. The telescope “takes away all that glare and background” so that “we can start to tease out the atmospheric composition” of the planet, said McCaughrean, who has worked on the Webb project for more than 20 years. Neptune appears deep blue in earlier images taken by the Hubble Space Telescope because of the methane in its atmosphere. Side-by-side photos of Neptune taken by Voyager 2 in 1989, Hubble in 2021 and Webb in 2022. Photo: AP However, near-infrared wavelengths recorded by Webb’s NIRCam primary imager show the planet as grayish white, with icy clouds piercing the surface. “The rings are more reflective in the infrared,” McCaughrean said, “so they’re much easier to see.” The image also shows a “fascinating brightness” near the top of Neptune, NASA said in a statement. Because the planet is tilted away from Earth and takes 164 years to orbit the sun, astronomers have yet to get a good look at its north pole. Webb also identified seven of Neptune’s 14 known moons. Looming above Neptune in a zoomed-out image is what appears to be a very bright sharp star, but is actually Triton, Neptune’s strange, massive moon with a halo of Webb’s famous diffraction spikes. Neptune and seven of its 14 known moons, including Triton (top left). Photo: Space Telescope Science Institute/ESA/Webb/AFP/Getty Images Triton, which is larger than dwarf planet Pluto, appears brighter than Neptune because it is covered in ice, which reflects light. Meanwhile, Neptune “absorbs most of the light that falls on it,” McCaughrean said. Because Triton orbits the wrong way around Neptune, it is believed to have once been a nearby Kuiper Belt object that was captured in the planet’s orbit. “So it’s really cool to go and take a look,” McCaughrean said. As astronomers scour the universe looking for other planets like ours, they’ve discovered that ice giants like Neptune and Uranus are the most common in our Galaxy. “By being able to see these in great detail, we can feed into our observations of other ice giants,” McCaughrean said. Operational since July, Webb is the most powerful space telescope ever built and has already released a wealth of unprecedented data. Scientists hope it will herald a new era of discovery. Research based on Webb’s observations of Neptune and Triton is expected next year. “The kind of astronomy we’re seeing now was unthinkable five years ago,” McCaughrean said. “Of course, we knew it would do that, we built it to do that, it’s exactly the machine we designed. But to suddenly start seeing things at these longer wavelengths, which were impossible before … is just absolutely remarkable.”
