Why do scientists think Neptune’s moon Nereid survived violent cosmic collision?

Neptune’s mysterious and distant moon Nereid could be the lone survivor of a violent cosmic collision that destroyed the planet’s original satellite system.

The new study led by Caltech planetary scientist Matthew Belyakov, proposed a new and transformative origin theory of Neptune’s third-largest moon Nereid.

The findings published in Science Advances, were based on data from the James Webb Space Telescope. According to the data, Nereid is not a captured Kuiper Belt object; but it is a sole survivor of the original satellite system that was destroyed 4 billion years ago.

As per astronomers’ observations, once stable planet planet Neptune became unstable when its largest moon Triton migrated from the outer solar system and entered the orbit of Neptune. The entry of Triton triggered orbital chaos and massive collisions.

But Nereid survived as the only remnant of that primordial group.

According to study author Matthew Belyakov, of Caltech, “What we know about Nereid is very limited. For its size, Nereid is extremely understudied.”

“I think Nereid is the only intact survivor of this process. The other survivors are Neptune’s 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,” he added.

JWST infrared observations revealed that Nereid’s surface is highly water-rich and contains CO2, with a signature that mirrors the "regular" moons of Uranus rather than the objects typically found in the Kuiper Belt.

Computer simulations show that when a body like Triton enters such a system, there is a roughly 25 percent chance that one or more original moons could be pushed into a distant, eccentric orbit rather than being destroyed. Researchers believe Nereid is that survivor.

Owing to Nereid's distance and faintness, visual confirmation remains limited to a single, blurry 1989 photograph from Voyager 2.

While the JWST data provides strong evidence for a reclassification of the moon's origin, scientists note that a dedicated future mission to Neptune would be required to fully understand the history of this unique satellite.