Webb Space Telescope Never-before-seen infrared observations of atmospheric and ring details
At an average distance of 2.8 billion miles (4.5 billion kilometers) from the Sun, Neptune lurks in one of the faintest parts of our solar system. Neptune has long confounded astronomers, with its strange moon Triton, complex rings, and roaring winds that blow faster than the speed of sound here on Earth. Only one spacecraft, Voyager 2, has ever visited this distant planet, and observations from both space and ground-based telescopes over the years have tracked the many turbulent storms. Now, NASA’s James Webb Space Telescope’s first look at this ice giant gives us a long-awaited glimpse of those clear rings and teases details about its mysterious storms. This image of the Neptune system, taken by Webb’s Near-Infrared Camera (NIRCam), reveals stunning views of the planet’s rings, not seen with this clarity for more than three decades. Webb’s new image of Neptune also captures details of the planet’s turbulent, stormy atmosphere. Neptune, an ice giant, has an interior that is much richer in elements heavier than hydrogen and helium, such as methane, than the gas giants Jupiter and Saturn. Methane appears blue in visible wavelengths, but, as seen in Webb’s image, this is not the case in the near infrared. Methane absorbs red and infrared light so strongly that the planet is quite dark at near-infrared wavelengths unless high-altitude clouds are present. These methane-ice clouds are visible in the Webb image as bright streaks and spots, reflecting sunlight before it is absorbed by the methane gas. To the upper left of the planet in this image, one of Neptune’s moons, Triton, also includes Webb’s characteristic eight diffraction peaks, an artifact of the telescope’s structure. Webb also captured 6 more of Neptune’s 14 known moons, along with a number of distant galaxies that appear as faint specks and a nearby star. Credits: Image: NASA, ESA, CSA, STScI, Image manipulation: Joseph DePasquale (STScI)
New Webb image captures clearest view of Neptune’s rings in decades
With its first image of Neptune, NASA’s James Webb Space Telescope is showing off its impressive capabilities closer to home. Webb not only captured the clearest view of this distant planet’s rings in more than 30 years, but his cameras also reveal details of the ice giant in a whole new light. What’s most striking about Webb’s new image is the crisp, clear view of the planet’s rings. In fact, some of these rings have not been detected since NASA’s Voyager 2 became the first spacecraft to observe Neptune during its flyby in 1989. In addition to several bright, narrow rings, the Webb image accurately reveals the fainter dust belts of Neptune. “It’s been three decades since we last saw these faint, dusty bands, and this is the first time we’ve seen them in the infrared,” notes Heidi Hammel. She is a multidisciplinary Webb scientist and an expert on the Neptune system. Webb’s extremely stable and precise image quality makes it possible to detect these very faint rings so close to Neptune. In this version of the Webb Near Infrared Camera (NIRCam) image of Neptune, the planet’s visible moons are highlighted. Neptune has 14 known moons, and seven of them are visible in this image. Triton, the bright spot in the upper left of this image, far outshines Neptune because the planet’s atmosphere is darkened by methane absorption at the wavelengths recorded by Webb. Triton reflects an average of 70 percent of the sunlight that hits it. Triton, which orbits Neptune in retrograde orbit, is thought to have originally been a Kuiper belt object gravitationally captured by Neptune. Since its discovery in 1846, Neptune has fascinated researchers. Located about 30 times farther from the Sun than Earth, Neptune orbits in the outer, dark region of the outer solar system. At this extreme distance, the Sun is so dim and tiny that midday on Neptune looks like a faint twilight on Earth. Due to the chemical composition of its interior, Neptune is characterized as an ice giant. The planet is much richer in elements heavier than hydrogen and helium compared to the gas giants Jupiter and Saturn. This is readily apparent in Neptune’s characteristic blue appearance in Hubble Space Telescope images at visible wavelengths, which is caused by small amounts of methane gas. In this image from Webb’s Near-Infrared Camera (NIRCam), a cluster of hundreds of background galaxies, varying in size and shape, appear alongside the Neptune system. Neptune, compared to Earth, is a large planet. If Earth were the size of a nickel, Neptune would be the size of a basketball. In most portraits, the outer planets of our solar system reflect this eerie size. However, Neptune appears relatively small in a broad view of the vast universe. In the lower left of this image, a barred spiral galaxy comes into focus. Scientists say this particular galaxy, which has not previously been explored in detail, may be about a billion light-years away. Spiral galaxies like this are typically dominated by young stars that appear blue at these wavelengths. NIRCam was built by a team at the University of Arizona and Lockheed Martin’s Advanced Technology Center. Credit: Image: NASA, ESA, CSA, STScI, Image manipulation: Joseph DePasquale (STScI) Neptune does not appear blue to Webb because the observatory’s Near-Infrared Camera (NIRCam) images objects in the near-infrared range from 0.6 to 5 microns. 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 are visible as bright streaks and spots, reflecting sunlight before it is absorbed by methane gas. These rapidly evolving cloud features have been captured over the years in images from other observatories, including the Hubble Space Telescope and the WM Keck Observatory. More subtly, a thin line of brightness encircling the planet’s equator could be a visual signature of the global atmospheric circulation that powers Neptune’s winds and storms. The atmosphere descends and warms at the equator, so it shines in infrared wavelengths more than the surrounding, cooler gases. Neptune’s 164-year orbit means that its north pole, at the top of this image, is just out of view for astronomers. However, the Webb images hint at an interesting brightness in this region. A previously known vortex at the south pole is evident in Webb’s view, but for the first time, Webb revealed a continuous band of high-latitude clouds surrounding it. (Click image to see full graph.) This image shows the science behind Webb’s diffraction spike patterns, showing how diffraction spikes occur, the effect of the primary mirror and struts, and the contribution of each to the diffraction spikes of Webb. Credits: NASA, ESA, CSA, Leah Hustak (STScI), Joseph DePasquale (STScI) Webb also captured seven of Neptune’s 14 known moons. This Webb portrait of Neptune is dominated by a very bright point of light bearing the characteristic diffraction spikes (see infographic above) 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 concentrated nitrogen, Triton reflects an average of 70 percent of the sunlight that hits it. In this image it far outshines Neptune because the planet’s atmosphere is dark from methane absorption at these near-infrared wavelengths. Triton orbits Neptune in an unusual backward (retrograde) orbit, leading astronomers to hypothesize that this moon was originally a Kuiper belt object that was gravitationally captured by Neptune. Additional Webb studies of both Triton and Neptune are planned next year. As the most powerful telescope ever built, the James Webb Space Telescope is the world’s premier space science observatory. It will solve mysteries in our solar system, look beyond distant worlds around other stars, and analyze the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners ESA (European Space Agency) and the Canadian Space Agency.
