Neptune stands out among the gas giants due to its unusual tilt and distinctive moons, which differ greatly from those of other gas giants. A recent study by Caltech researchers suggests that Triton, Neptune’s largest moon, may have destroyed the planet’s original moon system, sparing only one significant moon—Nereid.
To understand Neptune’s moon system, it’s important to note that Triton is peculiar. Its rotation is opposite to Neptune’s, indicating it didn’t form alongside the planet. It is likely a captured Kuiper Belt Object (KBO) binary, akin to Pluto and Charon.
Nereid is another anomaly.
Discovered in 1949 by Gerard Kuiper, after whom the Kuiper Belt is named, Nereid was Neptune’s only other known moon until the Voyager 2 flyby in 1989, over a century after Triton’s discovery. Its orbit is notably eccentric, with a highly elliptical path taking 360 days to complete. This led astronomers to believe for some time that it was another captured KBO.
However, the latest research strongly challenges this assumption.
Using JWST’s high-resolution infrared camera, researchers examined Nereid and found it resembles an icy moon from Uranus or Saturn more than a dark, dusty KBO. In infrared light, Nereid’s water-rich craters differ markedly from those of Phoebe, a known captured KBO.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>As highlighted in their paper, the researchers state, “Nereid’s unique spectrum among outer Solar System bodies is not consistent with a scenario where Nereid is captured during the early Solar System’s dynamic instability.”
This effectively rules out Nereid as a KBO, pointing instead to its origin as a natural moon of Neptune.
But why does it have such an unusual orbit?
Nereid’s distance, elliptical orbit, and other characteristics differ from most moons in the Solar System. To explore this, researchers used simulations.
By employing a dynamic simulator called REBOUND, they modeled Neptune with typical circular moons and then introduced Triton.
When Triton entered an eccentric, retrograde orbit, it caused chaos within Neptune’s existing moon system.
This resulted in most of the original moons being destroyed or ejected, contributing debris to Neptune’s current ring system and forming small “ring-moons” like Proteus.
However, the simulations revealed another aspect.
In about 20% of simulation runs, Triton’s arrival propelled one of Neptune’s native inner moons into a stable, elongated, and tilted orbit, akin to Nereid’s.
According to the simulations, Nereid might be an original moon of Neptune that was displaced into its current unusual orbit due to Triton’s capture.
If this theory holds true, Nereid could offer valuable insights into the formation of Neptune’s system, as its remote orbit may have kept it relatively unchanged compared to other gas giant moons.
Confirming this hypothesis will likely require sending another probe to Neptune, something scientists have been advocating for over a decade without success.
Until such a mission is realized, Nereid can be viewed not as a captured ice fragment but as a resilient survivor of a catastrophic event in the Solar System’s history.
The findings have been published in Science Advances.
This article was originally published by Universe Today. Read the original article.
