The NASA/ESA/CSA 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 particular planet’s rings in over 30 years, but his cameras also reveal the icy giant in a whole new light.
Most striking in Webb’s new image is the sharp view of the planet’s dynamic rings – some of which have not been seen at all, let alone with this clarity, since Voyager 2’s 1989 flyby. several narrow, bright rings, the Webb images clearly show Neptune’s fainter dust lanes. Webb’s extremely stable and accurate image quality also makes it possible to detect these very faint rings so close to Neptune.
Neptune has fascinated and perplexed researchers since its discovery in 1846. Located 30 times farther from the Sun than Earth, Neptune orbits in one of the darkest areas of our 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 NASA/ESA Hubble Space Telescope images at visible wavelengths, caused by small amounts of methane gas.
Webb’s Near Infrared Camera (NIRCam) captures objects in the near infrared range of 0.6 to 5 microns, so Neptune does not appear blue to Webb. In fact, methane gas is so strongly absorbent that the planet is quite dark at Webb 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 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 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; it is not a star, but Neptune’s most 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 because the planet’s atmosphere is darkened by the absorption of methane at Webb wavelengths. Triton orbits Neptune in a bizarre backward (retrograde) orbit, leading astronomers to speculate that this moon was actually 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 and the Canadian Space Agency. ESA’s main contributions to the mission are: the NIRSpec instrument; the optical bench assembly of the MIRI instrument; the provision of launch services; and personnel to support mission operations. In exchange for these contributions, European scientists will obtain a minimum share of 15% of the total observation time, similar to the NASA/ESA Hubble Space Telescope.