No spacecraft has visited Neptune since 1989, when NASA’s Voyager 2 spacecraft passed by on its way out of the solar system. Neptune, which is four times the width of Earth, is the most distant planet in our solar system. Voyager 2’s observations whet the appetites of astronomers, who were eager to learn more about the ice giant. Now we are back. About. On Wednesday, the James Webb Space Telescope cast its powerful gilded eye on this distant world. The power of this infrared camera, the largest and most advanced telescope ever sent into space, has provided some of our best views of Neptune in 30 years. “I’ve been waiting so long for these images of Neptune,” said Heidi Hammel, an interdisciplinary scientist at the Space Telescope Science Institute in Baltimore, which runs the Webb telescope. “I’m so glad it worked.” Ground-based observatories and the Hubble Space Telescope have taken many images of Neptune over the past three decades. But Webb’s views of Neptune, taken in July, provide an unprecedented look at the planet in infrared light. It took only a few minutes for the telescope to image Neptune up close, and another 20 to get a wider view, revealing not just the planet but myriad galaxies behind it that span the universe. “It’s aesthetically fascinating to see these distant galaxies and realize how small the ice giant looks,” said Klaus Pontoppidan, Webb program scientist at the Space Telescope Science Institute. Most prominent in the telescope view are Neptune’s rings, which appear to circle the planet at a slight tilt given its orientation to Earth. The Webb telescope will allow astronomers to measure the reflectivity of the rings, offering an unparalleled picture of this distant spectacle. New images could reveal the size and composition of these thin streaks, which are likely made of ice and other debris. “The ring system was absolutely mind-blowing to me,” Hammel said. “I haven’t seen it in this level of detail since the Voyager encounter in 1989. It just appears instantly.” Across the planet are bright spots believed to be methane ice clouds, which rise high into the planet’s sky and can persist for days. “No one really knows what these things are,” said Patrick Irwin, a planetary physicist at the University of Oxford. “They seem to come and go, a bit like cirrus clouds on Earth.” Future Webb observations could reveal how they form and what they are made of. The Webb images also show seven of Neptune’s 14 moons. The brightest is Triton, the planet’s largest moon, which scientists suspect was captured by Neptune’s gravity early in the solar system’s history. In infrared images, Triton’s frozen nitrogen surface makes it shine like a star, brighter than Neptune itself, because methane dims the planet in infrared light. NASA recently refused to send a mission to study Triton, and we can’t glean much about it from this image. But future observations by Webb should hint at the composition of Triton’s surface and could show changes that indicate geological activity. “Triton is a geologically active world,” Hammel said. “When Voyager 2 flew by, it saw cryovolcanoes erupting. So there is the potential for changes in surface chemistry over time. We will look for it.” Hammel also believes that a glimpse of Hippocampus, an eighth Neptune moon, is pictured directly above the planet. “It’s very faint, but it’s in the right location,” he said. These images of Neptune are just the latest in Webb’s tour of the solar system. This week we were treated to the telescope’s first glimpses of Mars, while over the summer we saw amazing views of Jupiter. Much more of our solar system will come under the observatory’s roving eye, including Saturn, Uranus and even distant icy objects beyond Neptune – like the dwarf planet Pluto. “It proves that we are an all-purpose observatory,” said Mark McCaughrean, Webb telescope scientist and senior science advisor to the European Space Agency. “We can observe very bright things like Mars and Neptune, but also very faint things. Everyone now sees that it works.” This article was originally published in the New York Times.
