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Astronomers have found rare evidence of a possible collision between two planet-like bodies around a young star about 11,000 light years from Earth.
The star, Gaia20ehk or Gaia-GIC-1, began dimming in visible light while becoming brighter in infrared, suggesting a cloud of hot dust was blocking and re-radiating its light.
Researchers say the debris may have formed after a major impact between large planetesimals, offering a rare glimpse into the violent process by which rocky planets can form.
The finding could help scientists understand how common moon-forming impacts may be in other young planetary systems.
A young star about 11,000 light years from Earth has given astronomers a rare chance to study what may be the aftermath of a collision between two planet-sized bodies.
The star, known as Gaia20ehk or Gaia-GIC-1, lies near the constellation Puppis. It was expected to behave like an ordinary, steady star. Instead, archived telescope data showed it had begun to dim and flicker in an unusual way.
Anastasios Tzanidakis, a doctoral candidate in astronomy at the University of Washington, was looking through older telescope observations from 2020 when he noticed that the star’s light had changed dramatically. For years, its brightness had been mostly stable. Then, from around 2016, it showed three dips in brightness. By 2021, its behaviour had become far more irregular.
“Stars like our sun don’t do that,” Tzanidakis said in a statement from the university.
The study, by Tzanidakis and James R A Davenport, was published on March 11, 2026, in The Astrophysical Journal Letters. The researchers say the most likely explanation is not a change in the star itself, but a large amount of dust and rocky debris passing in front of it as the material orbits the system.
Their preferred explanation is that this debris was produced by a recent collision between large planetesimals — early planet-like bodies that can grow into full-sized planets.
The evidence comes from an unusual pattern in the star’s light. In visible wavelengths, Gaia20ehk grew dimmer and more erratic. At the same time, infrared observations showed the system becoming brighter.
That combination is important. Dust can block visible light from a star when it passes in front of it. If the dust is warm, it can also glow in infrared light. The researchers say this “anti-correlated” behaviour — visible dimming alongside infrared brightening — is consistent with freshly generated circumstellar dust.
The study found that the system has remained bright in infrared for more than four years. Recent observations by the SPHEREx mission also confirm that the source is still infrared-bright.
The researchers estimate that the dust is about 900 Kelvin, or roughly 627°C. They also estimate a conservative dust mass of about 4 × 10²⁰ kg. In the discussion section of the study, they note that the mass could be larger depending on uncertainties such as the system’s distance and how much material is being detected.
The observations are especially interesting because the dust appears to be orbiting at roughly 1.1 astronomical units from the star. One astronomical unit is the average distance between Earth and the sun.
That does not mean the system is the same as our own early solar system. But it does make the event relevant to questions about how rocky planets form. The researchers say the collision may resemble, in broad terms, the kind of giant impact thought to have produced Earth’s moon about 4.5 billion years ago.
Planet formation is expected to be messy. In young solar systems, growing planetary bodies can collide, merge, break apart or be thrown into different orbits. Such impacts are thought to play a major role in building rocky planets. But observing them directly is difficult.
For astronomers to see the aftermath of such a collision, the geometry has to be favourable. The debris must pass between the star and Earth, blocking some of the star’s light. The event also plays out over years, making it harder to identify without long-term monitoring.
“Not many researchers are looking for phenomena in this way, which means that all kinds of discoveries are potentially up for grabs,” Davenport said.
Before the main infrared brightening, Gaia data showed a possible 380.5-day periodic signal in the star’s visible light. Based on an estimated stellar mass of 1.3 times that of the sun, the researchers say this is consistent with material orbiting at about 1.1 astronomical units.
The early dips reduced the star’s light by about 25 per cent and lasted around 200 days. Later, the dimming became more irregular and no clear periodic pattern remained. The authors suggest this could point to an evolving, uneven cloud of dust rather than a neat, compact object moving in a simple orbit.
The study identifies Gaia-GIC-1 as a likely young F-type star, based on its earlier spectral energy distribution. Follow-up optical spectroscopy did not reveal strong features, partly because the star is faint, highly variable and likely obscured by dust. The researchers also did not find clear signs of strong stellar accretion, which makes some alternative explanations less likely.
The authors are cautious in their interpretation. They describe Gaia-GIC-1 as a likely planetesimal collision afterglow, not as a confirmed collision.
They consider other possibilities, including the breakup of comet-like bodies, tidal disruption close to the star, or variability linked to young stellar objects. But the study says these explanations do not fit the available evidence as well as the collision scenario.
For example, a tidal breakup close to the star would be expected to produce much shorter dimming events than the 200-day dips seen in the data. The lack of strong emission lines also makes a typical young accreting star less likely.
Still, the researchers say more observations are needed. Continued optical and near-infrared monitoring could show how the dust cloud evolves. Observations with the James Webb Space Telescope could help measure the temperature and composition of the warm dust more precisely, including possible silicate features that would strengthen the impact interpretation.
Only a small number of possible giant-impact systems are known. The study says Gaia-GIC-1 may be the first likely planetesimal impact identified through Gaia’s long-term all-sky monitoring.
The discovery also points to the value of looking through years of telescope data for slow-changing events. Some astronomical events do not unfold in minutes or days, but over a decade.
Future surveys may find more such cases. Davenport suggested that the Vera C Rubin Observatory’s Legacy Survey of Space and Time, expected to begin later this year, could identify many more planetary impact candidates over the next decade.
That matters because scientists still do not know how common moon-forming impacts are, or how often rocky planets experience collisions that shape their final form. The study notes that warm dust from giant impacts appears to be relatively uncommon, occurring around only a few per cent of candidate young sun-like stars. This could mean such impacts are rare, or that their debris becomes too faint to detect quickly.