Neptune’s tiny moons may be the wreckage of shattered ancient worlds
JWST has uncovered surprising clues that Neptune’s strange inner moons may be the wreckage of an ancient cosmic catastrophe. Researchers detected clay-like minerals on Larissa, Galatea, and Neptune’s rings that form in the presence of liquid water—yet the moons themselves show no obvious water ice. The material likely came from deep inside much larger icy moons that were shattered when Triton was…
In 1989, Voyager 2 discovered six previously unknown moons around Neptune. Five of these tiny satellites orbit just beyond the planet's main rings. Investigating these distant and small moons has proven extremely challenging from Earth. Recently, NASA's James Webb Space Telescope (JWST) provided scientists with a closer look at Neptune's rings and three of its inner moons: Larissa, Galatea, and Proteus.
A team led by Caltech found a chemical composition unlike anything previously seen in outer solar system bodies. This discovery supports the theory that Neptune once had a very different family of moons. The original satellite system may have been shattered following the capture of Triton, Neptune's largest moon, from another location within the solar system.
The remnants from this violent event later coalesced to form the small inner moons orbiting Neptune today. According to Ryleigh Davis, a former Caltech graduate student and lead author of the paper published in Science Advances, Neptune stands out among the planets due to its unusual system of moons, which suggests a different history than other giant planets.
Independent support for this idea comes from another study led by Caltech postdoctoral scholar Matthew Belyakov, who found evidence that Nereid might be the only surviving moon from the original system. To understand the composition of Neptune's small moons, Davis and her colleagues used JWST's near-infrared spectrograph, which separates incoming light into different wavelengths to reveal the chemical composition of distant objects.
The team discovered magnesium-rich phyllosilicates, clay minerals that require liquid water to form. However, there was no evidence of water ice on any of the three moons or in the rings, which is especially puzzling because icy material is abundant in this region of the solar system. The unexpected presence of phyllosilicates led the researchers to hypothesize that the moons originated from a larger body that contained water ice deep within its structure.
Another mystery is the presence of a hydrated mineral on all three moons, but its exact composition remains unknown. The researchers are uncertain whether the material on the moons came from Neptune's first satellite system or from a large, differentiated Kuiper Belt object similar to Pluto that was torn apart by Neptune's gravity.
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