Neptune’s Moon Nereid: Survival from a Cosmic Collision

Neptune’s distant moon Nereid might be the last remaining original companion of the planet that survived a cosmic collision. This was reported by scientists on Wednesday. Among the sixteen known moons orbiting Neptune, Triton stands out as the largest. It originated from the solar system’s edges billions of years ago, disrupting Neptune’s original moons, leading them toward destructive paths.

A team from the California Institute of Technology utilized NASA’s Webb Space Telescope to study Nereid. Their findings suggest that unlike Triton, Nereid is not an intruder. Instead, it survived by adopting an extreme, elliptical orbit around Neptune. “Our knowledge of Nereid is minimal. It’s vastly understudied for its size,” stated study author Matthew Belyakov from Caltech. NASA’s Voyager 2 is the only spacecraft to have visited Neptune, making it there in 1989. Nereid was first discovered 40 years earlier by Dutch astronomer Gerard Kuiper, named after the sea nymphs in Greek mythology.

This moon spans around 220 miles (350 kilometers) in diameter and has an extraordinary orbit. Nereid takes about an Earth year to circle Neptune, moving from less than 1 million miles (1.4 million kilometers) from the planet’s surface to as far as 6 million miles (9.6 million kilometers).

Previously, scientists thought Nereid might have moved from the Kuiper Belt, a distant region of icy bodies. However, the Webb telescope showed that Nereid’s composition differs from typical Kuiper Belt objects due to its high ice content, indicating it was likely part of Neptune’s original system. “Few moons remain around Neptune,” Belyakov mentioned. The recent studies “strongly indicate” Nereid was not captured by Neptune’s gravity but instead remained from its original system. These results are published in the journal Science Advances.

Though not involved in the study, Carnegie Science planetary astronomer Scott Sheppard commended the findings. This research suggests, for the first time, that Nereid’s strange orbit aligns with the history we’d expect of a moon originally close to Neptune, later pushed out when Triton was captured. Belyakov’s team suggests Neptune’s innermost moons formed from the debris of those Triton destroyed. Among our solar system’s gas giants, Neptune has fewer moons, with Saturn boasting 292.

To confirm the origins of Neptune’s moons, scientists believe a visiting spacecraft would be valuable. However, no such missions are presently in development.

The Associated Press’ Health and Science Department is supported by the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP bears full responsibility for the article’s content.