No spacecraft has visited Neptune since 1989, when NASA’s Voyager 2 probe flew by on its way out of the solar system. Four times the size of Earth, Neptune is the most distant planet in our solar system. the appetite of astronomers, who were eager to learn more about the ice giant.
Now We have returned. Something like.
On Wednesday, the James Webb Space Telescope cast its mighty golden eye on this remote world. The power of this infrared machine, the largest and most advanced telescope ever sent into space, has provided some of our best views of Neptune in 30 years.
“I’ve waited so long for these images of Neptune,” said Heidi Hammel, an interdisciplinary scientist at the Space Telescope Science Institute in Baltimore, which directs the Webb telescope. “I’m so happy it worked out.”
Ground-based observatories and the Hubble Space Telescope have taken many images of Neptune over the last three decades. But Webb’s views of Neptune, taken in July, provide an unprecedented view of the planet in infrared light.
It took the telescope just a few minutes to get an image of Neptune up close, and another 20 to get a wider view, revealing not only the planet but also a myriad of galaxies behind it that stretch out into the cosmos. “It’s aesthetically fascinating to see those distant galaxies and get a sense of how small the ice giant looks,” said Klaus Pontoppidan, Webb project scientist at the Space Telescope Science Institute.
Most prominent in the telescope’s view are Neptune’s rings, which are seen circling the planet at a slight tilt given its orientation toward Earth. The Webb Telescope will allow astronomers to measure the reflectivity of the rings, offering an unparalleled view of this remote spectacle. New images could reveal the size and composition of these thin bands, which are likely made up of ice and other debris.
“The ring system was absolutely mind-blowing to me,” Dr. Hammel said. “I haven’t seen it in that level of detail since the Voyager encounter in 1989. It just jumps out at you.”
Across the planet are bright spots believed to be methane ice clouds, which rise into the planet’s skies 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 observations from the Webb telescope could find out how they form and what they are made of.
Webb’s 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 obscures the planet in infrared light. NASA recently refused to send a mission to study Triton, and not much can be gleaned from this image. But future Webb observations should hint at the composition of Triton’s surface and could show changes that indicate geological activity.
“Triton is a geologically active world,” Dr. Hammel said. “When Voyager 2 flew by, it saw cryovolcanoes erupting. So there is a possibility that there are changes in the surface chemistry over time. We’ll be looking for that.”
dr Hammel also believes that a glimpse of Hippocampus, an eighth Neptunian moon, is depicted just above the planet. “It’s very weak, but it’s in the right place,” he said.
These images of Neptune are just the latest in Webb’s tour of the solar system. This week they gave us the telescope. first glimpses of mars, while during the summer we saw incredible views of Jupiter. Much more of our solar system will be under the observatory’s roving eye, including Saturn, Uranus, and even remote icy objects beyond Neptune, such as the dwarf planet Pluto.
“It illustrates that we are a multi-use 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. Now everyone sees that it works.”