This James Webb Telescope image reveals Neptune's razor-thin ring system - Neptune's rings have not been seen so clearly since the Voyager-2 probe flew by some 30 years ago.
Neptune is the outermost planet in our solar system. The ice planet is about 30 times as far from the Sun as Earth and appears only as a bluish shimmering disk even with powerful Earth-based telescopes. Only the flyby of the Voyager-2 spacecraft in 1989 revealed details such as bright and dark storm vortices in Neptune's atmosphere and the existence of several faint dust rings around the planet. Since then, the Hubble Space Telescope has provided slightly sharper images of distant Neptune, but only parts of its rings were visible in these images.
That has now changed: NASA's new James Web Space Telescope has now targeted Neptune and its surroundings with its near-infrared camera (NIRCam). It shows the planet in the wavelength range from 0.6 to 5 microns and thus in the red and near-infrared range of light. As a result, Neptune does not appear blue in the Webb telescope image, as it does in visible light, but rather greyish. This is because the typical blue color of the two ice giants, Uranus and Neptune, is caused by the methane content in their gas envelope. In the red and near-infrared wavelength range, however, this gas absorbs almost all radiation, so the planet appears relatively colorless and dark.
However, this Webb telescope image also gives us the first clear image of Neptune's ring system since Voyager-2's flyby. "It's been three decades since we last saw these faint, dusty ribbons -- and this is the first time we've seen them in infrared," says Webb team member Heidi Hammel. The rings around Neptune's equator appear slightly tilted because the ice planet is currently turning the southern hemisphere more towards us on its 164-year orbit around the sun.
Also visible in this image are seven of Neptune's 14 known moons. Dominating the top of the image is Neptune's largest moon, Triton, with a diameter of around 2,700 kilometers. Its ice-covered surface also reflects the sunlight strongly in the near infrared. It far outshines Neptune and produces a radiating halo of latticed scattered light on camera. Six other, much smaller moons can be seen close to Neptune, some lying inside and some outside the arcs of the rings.