\n Astronomers suspect the reason for Triton\u2019s odd behavior is that it didn\u2019t originate from the remnants of Neptune\u2019s formation, which would make it orbit in the same direction as that planet. They hypothesize instead that Triton might have originated from the Kuiper Belt<\/a>, a ring-shaped region of icy bodies at the edge of the solar system, and entered the Neptunian environment over 4 billion years ago.\n <\/p>\n \n Previous<\/a> studies<\/a> have suggested that Triton may have been captured by Neptune\u2019s gravity after a close pass and flung inward to smash into Neptune\u2019s primordial satellite system.\n <\/p>\n \n If Neptune did have an original set of moons that more closely resembled those of its planetary neighbors, the arrival of Triton \u2014 which is just smaller than our own moon \u2014 would have wreaked havoc, crashing into the other satellites and annihilating some of them. The current features of Neptune\u2019s system support this scenario, and its seven inner moons appear to be leftovers<\/a> of this ancient clash.\n <\/p>\n \n But now, new research using data from the James Webb Space Telescope suggests that one object might have been entirely spared from the chaos.\n <\/p>\n \n \u201cI think Nereid is the only intact survivor of this process,\u201d 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<\/a> in the journal Science Advances.\n <\/p>\n \n \u201cThe other survivors are Neptune\u2019s innermost moons, but they are not intact because we have images of them from Voyager, and they look like disrupted rubble piles. So they are surviving material from the initial system, but not fully intact moons.\u201d\n <\/p>\n \n This hypothesis would upend previous assumptions that Nereid was, much like Triton and a few other Neptunian moons, a captured<\/a> Kuiper Belt object, as the new James Webb data revealed that Nereid\u2019s composition doesn\u2019t match what scientists know about Kuiper Belt objects.\n <\/p>\n \n Astronomers don\u2019t know a lot about Nereid, because it is faint and distant from Earth and the sun. The only image scientists have of it is a blurry photo taken in 1989 by NASA\u2019s Voyager 2 spacecraft during its brief fly-by of Neptune. Nereid is the outermost of Neptune\u2019s known moons, and it has one of the most eccentric (meaning noncircular) orbits in the solar system. It takes 360 Earth days<\/a> for the moon to complete one lap around Neptune.\n <\/p>\n \n Named after the sea nymphs of Greek mythology, Nereid is believed to be around 210 miles<\/a> (338 kilometers) in diameter. Even if it\u2019s part of an original set of moons that Neptune had shortly after its formation, about 4.5 billion years ago, it\u2019s difficult to speculate what that system might have looked like, according to Belyakov. \u201cIt\u2019s kind of anyone\u2019s guess what was there before Triton,\u201d he said.\n <\/p>\n \n Just like Triton, Nereid is an irregular satellite, a class of objects whose orbits are inclined, backward or distant from their host, suggesting they were captured by their host and previously orbited the sun independently.\n <\/p>\n \n But even among irregular satellites, Nereid is an outlier, Belyakov said. \u201cIt\u2019s twice as big in diameter as the next largest one, which is Phoebe around Saturn, and it\u2019s not all that distant from its host planet compared to a lot of the other irregular satellites.\u201d Some of Nereid\u2019s features, he added, have long made some astronomers doubt the moon\u2019s Kuiper Belt origin.\n <\/p>\n \n A 10-minute and 40-second observation commissioned for the study and made using James Webb\u2019s infrared capabilities, which can reveal the composition of a distant object, gives credence to those doubts.\n <\/p>\n \n \u201cWhat we found was an object that was highly water-rich on the surface, brighter than a lot of Kuiper Belt objects, and with some presence of CO2,\u201d Belyakov said. \u201cThe overall signature was more similar to that of regular satellites around Uranus rather than Kuiper Belt objects.\u201d The results were compared with data from 54 Kuiper Belt bodies, also from James Webb observations<\/a>.\n <\/p>\n \n Belyakov and his colleagues then performed computer simulations to test whether the hypothesis of Nereid as part of an original moon system would stand true. \u201cWhat we found in our simulations is that in the cases where Triton survives, rather than get destroyed or kicked into Neptune,\u201d Belyakov said, \u201caround 25% of the time one or more moons can survive the Triton encounter on distant orbits.\u201d That number compares favorably to the chances of Nereid being a captured object instead, he added.\n <\/p>\n \n In this scenario, in the first 100 million or 200 million years of solar system history, Triton would have slammed into the Neptunian system, colliding with a number of the original moons. But Nereid would have been spared and sent on an eccentric orbit instead. The event would have also slowed down Triton\u2019s own eccentric orbit and put it in its current path, closer to Neptune.\n <\/p>\n \n \u201cI think people have already wanted this to be true,\u201d Belyakov said about Nereid\u2019s possible new origin story. \u201cNow we can start the actual science feedback loop. There is more data to be gathered for Nereid compositionally that can help us really talk through the formation of the Neptunian system, and if we treat Nereid as a regular satellite, maybe that can tell us a lot about how satellites form around ice giants.\u201d\n <\/p>\n![\"Triton,](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/05\/1779315073_931_pia00317-large.jpg\")
<\/p>\n![\"Voyager](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/05\/1779315074_234_nereid-browse-732x520.jpg\")
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![\"Voyager](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/05\/1779315074_495_voyager-20260520142721511.jpg\")
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