Astronomers Spot Likely Giant Impact as Distant Star’s Light ‘Goes Bonkers’

For years, a young star about 11,000 light-years away behaved like a model of stability. Then, in 2016, its steady glow dipped three times. By 2021, its light curve — the record of its brightness over time — “went completely bonkers,” as the astronomer studying it put it.

Now, a team at the University of Washington says the most likely explanation is dramatic: two large rocky bodies on an Earthlike orbit slammed into each other, shrouding the star in hot debris. If that interpretation holds, it would be one of the clearest views yet of a giant planetary collision in another solar system — and a rare analogue to the violent impact thought to have created Earth’s moon.

“It’s incredible that various telescopes caught this impact in real time,” said Anastasios “Andy” Tzanidakis, a doctoral candidate in astronomy at the University of Washington and lead author of a study describing the event. “There are only a few other planetary collisions of any kind on record, and none that bear so many similarities to the impact that created the Earth and moon.”

The work, published March 11 in The Astrophysical Journal Letters, labels the object Gaia‑GIC‑1, short for “Gaia Giant Impact Candidate.” The host star is known in the European Space Agency’s Gaia catalog as Gaia20ehk.

A decade-long time-lapse of upheaval

The finding draws on years of observations from multiple space telescopes, including Gaia, NASA’s WISE and NEOWISE infrared surveyors, and early data from NASA’s SPHEREx mission. Together, they captured what amounts to a decade-long time-lapse of a planetary system in upheaval.

“The star’s light output was nice and flat, but starting in 2016 it had these three dips in brightness,” Tzanidakis said in a university news release. “And then, right around 2021, it went completely bonkers.”

The star appears to be a young F-type star — somewhat hotter and more massive than the sun — located toward the constellation Puppis in the Milky Way’s disk. Before 2016, it showed little variation in brightness. That changed with a trio of short-lived dimming events, each suggesting something passed between the star and Earth.

Even more telling was a subtle, repeating signal. By analyzing Gaia data collected before the system’s outburst, the team found that the star’s brightness rose and fell on a period of about 380.5 days. That regularity is consistent with an object orbiting the star at roughly 1.1 astronomical units — a distance similar to Earth’s orbit, scaled for the star’s higher mass.

“At that point, we knew there was something in this system on a roughly yearlong orbit,” said James R. A. Davenport, an assistant research professor at the University of Washington and co-author of the study. “Andy’s unique work leverages decades of data to find things that are happening slowly — astronomy stories that play out over the course of a decade.”

Dust that’s too hot to be a distant comet belt

Around 2020 and 2021, the system’s behavior changed dramatically. In visible light, Gaia20ehk began to dim and brighten by large amounts in an irregular pattern, as if massive, uneven clouds were passing across the star. At the same time, its infrared output surged and stayed high for years.

Infrared observations from WISE and its extended NEOWISE mission, followed by early SPHEREx data, showed that the system became far brighter at wavelengths where warm dust glows. From the color of that infrared light, the team estimated the dust to be about 900 kelvins — roughly 600°C (more than 1,100°F).

That temperature points to debris very close to the star, not to a cold, distant belt of comets or asteroids. Modeling the amount of light blocked and emitted by the dust, the researchers concluded that at least one dominant clump has a projected area of about 0.13 square astronomical units — large enough to rival or exceed the orbit of Mercury in cross-section. The minimum mass of the optically thick clumps is on the order of 4 × 10²⁰ kilograms, several thousand times the mass of the asteroid Ceres, with the total debris likely far higher.

A collision that echoes the Moon’s origin — with caveats

The picture that best fits the data, the authors say, is that two rocky bodies — planets or large planetesimals — on intersecting paths at around 1 astronomical unit collided catastrophically.

“At first, they had a series of grazing impacts, which wouldn’t produce a lot of infrared energy,” Tzanidakis said. Those earlier brushes could account for the modest dips in 2016 and the pre-impact modulation in the light curve. “Then, they had their big catastrophic collision, and the infrared really ramped up.”

In that scenario, the final high-speed impact would have vaporized and shattered vast amounts of rock, launching a cloud of molten droplets, vapor and dust into orbit around the star. As that debris expanded, it would glow brightly in the infrared while condensing and cooling. Clumps and filaments of dust moving along the orbit would repeatedly pass between the star and Earth, causing deep, irregular fades in visible light.

The idea closely parallels the leading explanation for how Earth’s moon formed. In the giant-impact hypothesis, a Mars-size protoplanet often called Theia struck the young Earth about 4.5 billion years ago. The collision sprayed molten and vaporized rock into orbit, eventually coalescing into the moon and reworking Earth’s crust and spin.

The team behind Gaia‑GIC‑1 stops short of claiming that they have found a fully fledged moon-forming event. The paper describes the system as a “catastrophic planetesimal collision candidate,” and the authors emphasize the uncertainties. They cannot directly see the colliding bodies, only their inferred debris, and estimates of the debris mass carry wide margins of error.

Alternative explanations exist. Other researchers have suggested that some infrared-bright events in young systems could come from a runaway breakup of icy comets or swarms of smaller rocky bodies, or from instabilities in a dusty disk without a single, dominant impact.

In this case, the Washington team argues that the combination of clues — a pre-impact orbital period near 1 AU, the scale and temperature of the dust, the timing of the infrared surge, and the multi-year evolution — all favor a large collision rather than gradual grinding of smaller objects.

“Is it two full-size terrestrial planets, or something a bit smaller? We don’t know yet,” Davenport said. “But whatever hit, it was big enough and violent enough to completely transform this inner planetary system.”

Why time-domain surveys are changing what we can see

Only a small number of similar events have been identified. Previous candidates include systems such as BD+20 307 and HD 166191, where sudden changes in infrared emission have been linked to suspected giant impacts. But in many cases, astronomers have had only two or three snapshots taken years apart, not a continuous record before and after.

Gaia‑GIC‑1 stands out because it was watched in multiple wavelengths over nearly a decade, from a relatively calm state through the onset of chaos and into a sustained dusty aftermath.

That kind of coverage is becoming possible thanks to time-domain surveys — projects designed to repeatedly scan large swaths of the sky and track how they change. Gaia, launched in 2013, made precise brightness measurements of more than a billion stars over roughly 10 years. WISE and NEOWISE have been mapping the sky in infrared light since 2010. SPHEREx, launched in 2025, is adding detailed infrared spectra over the entire sky.

The University of Washington team also points ahead to the Vera C. Rubin Observatory in Chile, expected to begin full operations in the coming years. Its Legacy Survey of Space and Time will image the southern sky every few nights for a decade, capturing hundreds of petabytes of data on transient and variable objects.

Davenport estimated that over 10 years, Rubin could find on the order of 100 similar planetary impact events, turning rare curiosities into a statistical sample.

“How rare is the event that created the Earth and moon?” he said. “That question is fundamental to astrobiology.”

What comes next

The answer matters because the moon plays a central role in Earth’s long-term stability. Its gravity helps steady the planet’s axial tilt, moderating seasons, and drives tides that may have influenced early life and geologic activity. If moon-forming collisions are common around sunlike stars, then Earth–moon-style systems could be a frequent outcome of planetary formation. If they are rare, Earth’s configuration might be unusual.

For now, Gaia‑GIC‑1 offers just one more data point, albeit a vivid one. Astronomers plan to keep monitoring Gaia20ehk to see whether the dust disperses, the infrared glow fades, or the pattern of optical dimming changes as debris spreads and cools.

From Earth, the collision that may eventually create a calm, stable planetary system appears as a star that went suddenly and spectacularly wrong. In cosmic terms, that flare of chaos is a reminder that tranquil worlds are often born from violent beginnings — and that somewhere in the direction of Puppis, a story like our own may be playing out in slow motion.