NASA’s James Webb Space Telescope shows off its capabilities closer to home with its first image of Neptune. Not only has Webb captured the clearest view of this distant planet’s rings in over 30 years, but his cameras reveal the icy giant in a whole new light.
Most striking in Webb’s new image is the sharp view of the planet’s rings – some of which have gone undetected since NASA’s Voyager 2 became the first spacecraft to observe Neptune during its 1989 flyby. In addition to several bright, narrow rings, the Webb image clearly shows Neptune’s fainter dust lanes.
“It’s been three decades since we’ve seen these faint, dusty rings, and this is the first time we’ve seen them in the infrared,” notes Heidi Hammel, Neptune system expert and interdisciplinary scientist for Webb. Webb’s extremely stable and accurate image quality makes it possible to detect these very faint rings so close to Neptune.
Neptune has fascinated researchers since its discovery in 1846. Located 30 times farther from the Sun than Earth, Neptune orbits in the dark and remote region of the outer solar system. At this extreme distance, the Sun is so small and dim that noon on Neptune is like a dark twilight on Earth.
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 heavier elements than hydrogen and helium. This is evident in Neptune’s characteristic blue appearance in Hubble Space Telescope images at visible wavelengths, caused by small amounts of methane gas.
Webb’s Near Infrared Camera (NIRCam) images objects in the near infrared range of 0.6 to 5 microns, so Neptune does not appear blue to Webb. In fact, methane gas absorbs red and infrared light so strongly that the planet is quite dark at those near-infrared wavelengths except where high-altitude clouds are present. These clouds of methane and ice are prominent as bright streaks and spots, which reflect sunlight before it is absorbed by the methane gas. Images from other observatories, including the Hubble Space Telescope and the WM Keck Observatory, have recorded these rapidly changing cloud features over the years.
More subtly, a thin line of brightness circling the planet’s equator could be a visual signature of the global atmospheric circulation that powers Neptune’s winds and storms. The atmosphere sinks and warms at the equator, and therefore glows more at infrared wavelengths than the cooler surrounding gases.
Neptune’s 164-year orbit means its north pole, at the top of this image, is just out of sight for astronomers, but the Webb images suggest intriguing brightness in this area. 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.
Webb also captured seven of Neptune’s 14 known moons. Dominating this Webb portrait of Neptune is a very bright point of light sporting the signature diffraction peaks seen in many Webb images, but it is not a star. Rather, it is Neptune’s large and unusual moon, Triton.
Coated in an icy sheen of condensed nitrogen, Triton reflects an average of 70% of the sunlight that strikes it. It far surpasses Neptune in this image because the planet’s atmosphere is darkened by the absorption of methane at these near-infrared wavelengths. Triton orbits Neptune in an unusual backward (retrograde) orbit, leading astronomers to speculate that this moon was originally a Kuiper Belt object that was gravitationally captured by Neptune. Additional Webb studies of Triton and Neptune are planned for the coming year.
The James Webb Space Telescope is the world’s first space science observatory. Webb will solve the mysteries of our solar system, look beyond distant worlds around other stars, and probe 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.