The most surprising in Webb’s new image is the sharp view of the planet’s rings, some of which had not been detected since NASA’s Voyager 2 spacecraft became the first spacecraft to observe Neptune during its flyby in 1989. In addition to several bright, narrow rings, Webb’s image clearly shows Neptune’s fainter dust lanes.
“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.“, said HeidiHammel, an expert on the Neptune system and an interdisciplinary scientist on Webb’s team. Webb’s extremely stable and precise image quality makes it possible to detect these very faint rings that are so close to Neptune.
Neptune and its rings
Neptune has fascinated researchers since its discovery in 1846. 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.
This planet is characterized as a 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 the hydrogen and helium. This is readily apparent in Neptune’s characteristic blue appearance from Hubble Space Telescope images in the visible wavelengths, caused by small amounts of gaseous methane.
The infrared camera close to Webb, NIRCamgenerates images of objects in the near infrared range between 0.6 and 5 microns, so Neptune doesn’t look blue through Web 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 high-altitude clouds are present. Such methane ice clouds they 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 fuels Neptune’s winds and storms. The atmosphere sinks and heats up at the equator, and therefore shines brighter in infrared wavelengths than the cooler surrounding gases.
Neptune’s 164-year orbit means its north pole, at the top of this image, is out of sight of astronomers, but Webb’s 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.
moons of neptune
Webb also captured seven of Neptune’s 14 known moons.. A very bright point of light stands out in this image 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.
September 21, 2022
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