Recent observations of Neptune’s moons and rings are revealing evidence of a past catastrophe billions of years ago, involving a Pluto-sized object that caused a cosmic chaos. NASA’s James Webb Space Telescope analyzed three of Neptune’s small inner moons—Proteus, Larissa, and Galatea—and its dusty inner rings, discovering clay minerals typically found deep inside distant solar system objects. These magnesium-rich minerals are also present on the dwarf planet Ceres, orbiting the asteroid belt between Mars and Jupiter, and have been identified in some meteorites.
“These minerals form only after long-term contact between liquid water and rock,” explained Ryleigh Davis, a planetary scientist and lead author of the study published in Science Advances. Since Neptune’s small moons are too cold and tiny to have created such minerals in place, they must have originated elsewhere—probably from the interior of a much larger, ancient planet. The presence of this material suggests a catastrophic event that destroyed early worlds, exposing their core material, which later coalesced into the current moons and rings.
The study points to Triton, Neptune’s biggest moon, as the likely culprit. Once residing farther out in the Kuiper Belt, Triton was captured by Neptune’s gravity within the first billion years after the solar system formed, around 4.5 billion years ago. During this chaotic period, Neptune’s gravitational influence stirred up its original moons, leading to collisions that resulted in debris, which eventually reformed into Neptune’s current inner moons and rings.
Unlike the regular, circularly orbiting large moons of Jupiter, Saturn, and Uranus—formed in a more orderly fashion—Neptune’s satellite system is dominated by a captured object, Triton, which accounts for over 99% of the system’s mass. Triton orbits Neptune in the opposite direction of the planet’s spin, a trait characteristic of captured objects rather than moons formed alongside their planets.
Neptune has 16 known moons, including Nereid, which has one of the most elliptical orbits in the solar system. Nereid is believed to be the only survivor among Neptune’s original moons, having somehow escaped Triton’s destructive influence. Triton itself resembles Pluto in composition, with surfaces covered in nitrogen, methane, and carbon dioxide ices, and possessing a thin nitrogen atmosphere.
The findings also consider an alternative theory—that another large Kuiper Belt object may have drifted too close to Neptune and was torn apart by its gravity—but the evidence strongly favors Triton’s capture as the primary event. This saga reminds us of the violent past of our solar system, illustrating how a single cosmic incident can radically alter the architecture of a planetary system.