Le télescope Webb trouve des signes d'une catastrophe ancienne sur les lunes de Neptune

NASA’s James Webb Space Telescope has uncovered compelling evidence suggesting that Neptune endured a violent cosmic upheaval billions of years ago, likely triggered by the capture of a Pluto-sized object. The findings, based on detailed analysis of the composition of Neptune’s inner moons and rings, point to a dramatic collision event that reshaped the planet’s satellite system. The research team focused on three of Neptune’s smallest inner moons, Proteus, Larissa, and Galatea, as well as its inner dusty rings. Using data collected by the Webb telescope, scientists identified the presence of clay-like minerals rich in magnesium. Such materials typically form under conditions involving extended interaction between liquid water and rock, a process that would require temperatures and pressures far beyond what exists on these distant, frigid moons. Ryleigh Davis, a planetary scientist at the University of California, San Diego and lead author of the study published in Science Advances, explained that the moons themselves could not have generated such minerals due to their size and temperature. Instead, the clay must have originated from the interior of a much larger body, one that was later shattered in a massive impact event. This discovery implies that Neptune once hosted a different set of moons, whose remnants now constitute the moons and rings observed today. According to the study, the cause of this disruption is believed to be Triton, Neptune’s largest moon. Unlike the other major moons of the gas giants, Triton does not orbit in the same direction as Neptune’s rotation. This retrograde motion strongly indicates that Triton did not form alongside Neptune but was instead captured from the Kuiper Belt, a region beyond Neptune populated by icy bodies. Scientists estimate that Triton was captured by Neptune approximately four billion years ago, during a period of intense gravitational chaos in the early solar system. At that time, the gas giants were still migrating toward their present positions. Triton’s arrival disrupted Neptune’s existing moon system, triggering widespread collisions among the planet’s original satellites. These collisions led to the destruction of many of Neptune’s initial moons, with the debris coalescing into the moons and rings that remain today. Triton, which dominates Neptune’s satellite system by mass, accounts for over 99 percent of the total mass of all of Neptune’s moons and rings combined. Unlike the other gas giants, Jupiter, Saturn, and Uranus, whose moons formed in a relatively stable, orderly fashion, Neptune’s satellite system lacks this structure. Instead, it features a dominant, captured moon and a collection of smaller, irregularly shaped moons. This anomaly underscores the unique history of Neptune compared to its planetary neighbors. Among Neptune’s moons, Nereid stands out as an exception. It exhibits one of the most eccentric orbits in the solar system and shows signs of having survived the tumultuous era following Triton’s capture. Its composition suggests it may have been one of the few original moons to avoid complete destruction. Triton itself bears similarities to Pluto, sharing characteristics such as surface features composed of nitrogen ice, methane ice, and other volatile compounds. However, unlike Pluto, Triton is locked in a slow, retrograde orbit around Neptune, reinforcing the theory that it was captured from the Kuiper Belt. The discovery adds new insights into the dynamic processes that shaped the outer solar system. By studying the remnants of this ancient catastrophe, scientists hope to better understand how planetary systems evolve over time and how such events might influence the formation of moons and rings elsewhere in the cosmos. Further studies will focus on analyzing additional data from the Webb telescope to confirm the presence of other materials that may have been brought to Neptune by the captured object. Researchers aim to refine their understanding of the timing and scale of the event, shedding light on the broader context of planetary migration and the evolution of the solar system.