Deep in space, mysterious wanderers roam freely — of planetary masses yet not hosted by stars. These celestial nomads, called planetary-mass objects (PMOs), have baffled astronomers since their discovery in 2000. How were these cosmic orphans born?

On Thursday, an international team led by China's Shanghai Astronomical Observatory cracked the code in Science Advances: Violent collisions between newborn stars' gaseous disks in crowded stellar nurseries are mass-producing these rogue worlds. The discovery not only solves a 25-year-old puzzle but also may rewrite cosmic classification rules.

Their unique formation channel gives them defining characteristics that set them apart from stars and planets.

Scientists say that two theories previously attempted to explain their origins. One is "Failed Stars" hypothesis, which says that PMOs might form directly from collapsing molecular clouds, but their small size prevents nuclear fusion.

The other is "Exiled Planets" hypothesis which claims that PMO could be gas giants ejected from host stars via gravitational slingshots.

Both theories were disproven by new evidence. NASA's James Webb Space Telescope (JWST) observed hundreds of PMOs in Orion's Trapezium Cluster — a vast population far exceeding predictions of the "Failed Star" hypothesis.

About 9 percent exist as binary/triplet systems, which is unlikely for exiled planets, and many host expansive gas disks up to 200 astronomical units wide — structures indicating a formation history with no stars in sight.

"PMOs are neither stunted stars nor runaway planets," said lead researcher Deng Hongping of Shanghai Astronomical Observatory. "They're products of cosmic chaos."

The team focused on dense stellar nurseries like the Trapezium Cluster, where thousands of new stars crowd within 10 light-years. Each star is surrounded by a circumstellar disk — a rotating ring of gas and dust where planets form.

The research team simulated this process using supercomputer-powered models. When two young stars pass by each other at specific speeds and distances, gravitational forces stretch their circumstellar disks (rotating rings of gas and dust), creating elongated, high-density tidal bridges. These bridges then collapse under their own gravity, forming independent PMOs — some even emerging as paired binary systems.

"The Trapezium Cluster is the ultimate PMO factory — its crowded, fast-moving stars maximize collisions," Deng said.

China's Earth 2.0 space telescope, expected in 2028, will hunt for PMOs using microlensing, a technique predicted by Einstein's relativity to detect invisible objects via the gravitational warping of light.

"As data pours in, we may soon map these comic orphans across our home galaxy," Deng said.