Neptunian moon Nereid could be lone intact survivor from ancient satellite system

Neptune’s third-largest moon, Nereid, may be the only surviving moon from an ancient group of moons destroyed early in the solar system’s history, according to a new analysis based on data from the James Webb Space Telescope.

Neptune, the eighth and furthest planet from the sun among the outer planets of our solar system, stands out with its strange moon group. The other outer giants (Uranus, Saturn, and Jupiter) all have a generally similar, regular cluster of moons; several large moons orbit in the same direction as the parent planet’s rotation.

But Neptune has a much smaller and more chaotic collection of moons: TritonNeptune’s largest moon dwarfs the others and orbits in the opposite direction of its host’s rotation. It is the only large moon in the solar system that can do this.

Astronomers suspect that the reason for Triton’s strange behavior is that it is not due to remnants of Neptune’s formation, which caused it to orbit in the same direction as the planet. Instead, they hypothesize that Triton may have come from there. Kuiper BeltA ring-shaped region of icy bodies at the edge of the solar system entered the Neptunian environment 4 billion years ago.

Pre studies They suggested that Triton may have been captured by Neptune’s gravity after a close flyby and thrown inward, impacting Neptune’s primitive satellite system.

If Neptune had an original set of moons more similar to those of its planetary neighbors, the arrival of Triton, which is slightly smaller than our moon, would have wreaked havoc by crashing into other moons and destroying some of them. The current characteristics of Neptune’s system support this scenario, and so do its seven inner moons. the rest of this ancient conflict.

But now, new research using data from the James Webb Space Telescope suggests that an object may have completely escaped the chaos.

“I think Nereid is the only one that survived this process intact,” said Matthew Belyakov, a graduate student in planetary science at the California Institute of Technology and first author of a study on the subject. Published Wednesday In the journal Science Advances.

“The other surviving moons are Neptune’s innermost moons, but they’re not intact because we have images from Voyager and they look like piles of fragmented debris. So they’re carrying material from the initial system, but they’re not completely intact moons.”

This hypothesis would overturn previous assumptions that Nereid was a moon, like Triton and several other Neptunian moons. caught Kuiper Belt object, new James Webb data reveals Nereid’s composition does not match what scientists know about Kuiper Belt objects.

A pixelated image

Astronomers don’t know much about Nereid because it is faint and far from Earth and the sun. The only image scientists have is a blurry photograph taken in 1989 during NASA’s Voyager 2 spacecraft’s brief flyby near Neptune. Nereid is the outermost of Neptune’s known moons and has one of the most eccentric (meaning non-circular) orbits in the solar system. takes 360 Earth days For the Moon to make one revolution around Neptune.

Nereid, named after the sea nymphs in Greek mythology, is believed to be around here. 210 miles (338 kilometers) in diameter. According to Belyakov, it is difficult to predict what this system might look like, even if it were part of the original group of moons that Neptune had shortly after its formation about 4.5 billion years ago. “Anyone can guess what was there before Triton,” he said.

Like Triton, Nereid is an irregular satellite; a class of objects whose orbits are inclined, backward, or away from their host; this suggests that they were captured by their host and previously orbited the Sun independently.

But even among irregular moons, Nereid is an outlier, Belyakov said. “It is twice as large in diameter as Phoebe, the next largest moon around Saturn, and not that far from the host planet compared to many other irregular moons.” He added that some features of Nereid have long led some astronomers to doubt the origin of the moon’s Kuiper Belt.

A 10-minute, 40-second observation commissioned for the study, made using James Webb’s infrared capabilities that can reveal the composition of a distant object, reinforces these suspicions.

“What we found was an object that was quite rich in water on its surface, was brighter than many Kuiper Belt objects, and contained some CO2,” Belyakov said. “The overall signature was more similar to the signature of normal moons around Uranus rather than Kuiper Belt objects.” The results were compared with data from 54 Kuiper Belt bodies. James Webb’s observations.

Belyakov and his colleagues then ran computer simulations to test whether the hypothesis that Nereid was part of the original lunar system would be correct. “What we found in our simulations is that one or more moons could survive a Triton encounter in distant orbits in about 25% of cases if Triton survived rather than being destroyed or thrown into Neptune,” Belyakov said. He added that this number compared favorably to the possibility of the Nereid being a possessed object.

In this scenario, during the first 100 million or 200 million years of solar system history, Triton would have crashed into the Neptune system, colliding with several of the original moons. However, Nereid would have been spared and sent into an eccentric orbit instead. The event would also have slowed Triton’s own eccentric orbit, putting it on its current path closer to Neptune.

“I think people already want it to be true,” Belyakov said of Nereid’s possible new origin story. “Now we can start the real science feedback loop. There’s more data to collect for Nereid in terms of composition, and that can help us really talk about the formation of the Neptune system, and if we treat Nereid as a normal moon, maybe that can tell us a lot about how moons form around ice giants.”

More observations from James Webb might help, but the final word on what the Nereid was really like would require a mission to Neptune. There is nothing planned at the moment and Traveler 2Launched in 1977, it is the only spacecraft to study the system.

‘An interesting idea’

The new study is a nice, simple examination of how the Neptune moon system came to be what it is today, according to Carolyn Porco, an American planetary scientist who worked on NASA’s Voyager and Cassini missions and was not involved in the new study.

“The captured body was Triton, which then caused havoc by gravitationally scattering Neptune’s original moons here and there, mostly outside Neptune’s orbit,” Porco wrote in an email. “The authors show that it is plausible that Nereid lucked out by remaining in orbit around Neptune but at a much greater distance than Triton. This explains why its composition observed by James Webb does not match objects in the Kuiper Belt.”

Leigh Fletcher, a professor at the Faculty of Physics and Astronomy at the University of Leicester in England, who was not involved in the study, said James Webb once again demonstrated his enormous power as a solar system explorer.

“We have long known that there is something special about Neptune’s collection of moons, which have been severely disrupted by the arrival of Triton and other moons captured by Neptune’s gravity over the years,” Fletcher wrote in an email. “Given these destructive processes, I don’t think we expected anything but rubble and debris to remain from Neptune’s original moon system.”

But James Webb data suggests otherwise, he added, and further work with the telescope could reveal finer-scale features, perhaps strengthening the claim that Nereid is an original moon. “This is an intriguing idea and something that can certainly be tested with future JWST observations and an ambitious future mission to the Neptune system.”

Sign up CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific breakthroughs and more.

For more CNN news and newsletters, create an account at: CNN.com