CAPE CANAVERAL, Fla. — Scientists have revealed that Neptune’s distant moon Nereid might be the sole survivor of the planet’s original companions, following a cosmic collision. Neptune, the eighth and most distant planet in our solar system, hosts sixteen known moons. The largest, Triton, disrupted the original moons billions of years ago due to its entrance from the solar system’s cold outskirts, leading to destructive trajectories for the other moons.
A research team from the California Institute of Technology utilized NASA’s Webb Space Telescope to investigate Nereid. Their findings suggest that Nereid differs from Triton, avoiding a collision by settling into its highly elliptical orbit around Neptune. Matthew Belyakov from Caltech stated, “We have limited knowledge about Nereid. Despite its size, it remains significantly understudied.”
“What we know about Nereid is very limited. For its size, Nereid is extremely understudied,” — Matthew Belyakov, Caltech.
Neptune has only seen one spacecraft visit, NASA’s Voyager 2 in 1989. Nereid itself was discovered four decades earlier by Dutch astronomer Gerard Kuiper, who named it after mythical sea nymphs. Nereid measures about 220 miles (350 kilometers) across and has a notably eccentric orbit. It requires nearly a full Earth year to complete an orbit around Neptune.
The moon’s path spans less than 1 million miles (1.4 million kilometers) from Neptune at its closest, extending to 6 million miles (9.6 million kilometers) at its furthest. Initially, it was suspected that Nereid migrated from the Kuiper Belt region similar to other moons in the outer solar system. However, analysis using the Webb telescope revealed a composition inconsistent with Kuiper Belt objects because of its abundant ice content, indicating it belonged to Neptune’s system from the beginning.
Due to the limited number of moons left in Neptune’s system, Belyakov comments, “We don’t have all that much evidence left around Neptune.” Recent observations effectively dismiss the notion that Nereid was an interloper ensnared by Neptune’s gravitational pull.
The observations show that Nereid’s odd orbit aligns with a moon that originally formed close to Neptune, later moved outward when Triton was captured.— Scott Sheppard, Carnegie Science.
According to Carnegie Science planetary astronomer Scott Sheppard, these observations are a significant breakthrough, demonstrating for the first time that Nereid’s unusual orbit aligns with its history. It likely began close to Neptune and was forced outwards following Triton’s capture.
Belyakov and his team suggest that Neptune’s inner moons might have formed from the remnants of those destroyed by Triton. Despite Neptune hosting fewer moons compared to the other giant planets, Saturn remains the leader with 292 moons.
Although no current missions are planned, a visiting spacecraft could potentially provide a definitive account of Neptune’s moon formation history.
The research findings have been published in the journal Science Advances.
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