Astronomers Find Signs of Ancient Disaster That Destroyed 'Ancient Worlds'

Scientists have found new clues about a huge disaster that happened near Neptune billions of years ago. Using NASA's James Webb Space Telescope, researchers discovered that a Pluto-sized object crashed into Neptune's neighborhood and destroyed the planet's original moons. The findings were published in the journal Science Advances and were led by planetary scientist Ryleigh Davis from the University of California, San Diego.

The key clue was a type of clay mineral found on three of Neptune's small inner moons — Proteus, Larissa, and Galatea — as well as on its dusty inner rings. These minerals are rich in magnesium and normally form only when liquid water and rock stay in contact for a very long time. That kind of chemistry cannot happen on tiny, freezing-cold moons like these, so scientists knew the minerals must have come from somewhere else.

Davis explained that the clay had to come from deep inside a much larger, ancient world. When that world was destroyed, its hidden interior was exposed and scattered into space. The small moons and rings we see around Neptune today likely formed from that leftover debris. In a way, Neptune's inner moons are like pieces of a destroyed world turned inside out.

Researchers believe the culprit behind this disaster was Triton, Neptune's largest moon today. Triton was not always one of Neptune's moons — it used to roam the outer solar system in a region called the Kuiper Belt. About four and a half billion years ago, during a wild and chaotic time when planets were still moving into their final orbits, Neptune's gravity grabbed Triton and pulled it in.

Triton is a bit bigger than Pluto and much smaller than Earth's Moon. Once captured, Triton's gravity stirred up all of Neptune's original moons and caused most of them to crash into each other. The current inner moons of Neptune slowly formed from the wreckage left behind after those collisions.

One of the biggest clues that Triton was not an original moon is the direction it travels. It orbits Neptune in the opposite direction of the planet's spin, which is very unusual. Every other large moon around the giant planets — Jupiter, Saturn, and Uranus — orbits in the same direction as its planet rotates, because those moons formed right alongside their planets.

Neptune is the only giant planet in our solar system that does not have an orderly family of large moons. Instead, the captured intruder Triton now makes up more than 99% of the total mass of everything orbiting Neptune. Scientists say one of Neptune's outer moons, Nereid, appears to be the only survivor from the original moon system, somehow escaping the chaos that Triton caused.

Triton itself is a fascinating world. It has nitrogen ice, methane ice, and carbon dioxide on its surface, along with a thin nitrogen atmosphere — making it similar to Pluto in many ways. Scientists think Neptune's inner moons may be a unique window into the deep interiors of icy worlds, since events like this are very rare anywhere else in the solar system.

Davis noted that the story of Neptune's moons is a reminder that the solar system has a violent history. A single unexpected event, like one wandering moon getting captured by a planet's gravity, can completely change the way an entire planetary system looks. 'It's a vivid example of how a single random event can fundamentally alter a planetary system's architecture,' Davis said.