Astronomers believe they have spotted one of the rarest sights in space: two planets slamming into each other around a distant star.
The collision appears to have occurred about 11,000 light-years from Earth, around a Sun-like star called Gaia20ehk, near the constellation Puppis (the “bathtub cover”). The researchers say the crash may reflect the gigantic impact it is thought to have formed the earth and the moon billions of years ago, giving scientists a rare window into how celestial bodies take shape. The findings were published on 11 March i The Astrophysical Journal Letters.
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A star who suddenly “went to hell”
Planetary collisions are thought to be common in young star systems, but they are difficult to detect. The planets must have orbits that take them directly in front of their home star, so that debris blocks parts of the star’s light, which telescopes can detect and measure in both the visible and infrared light.
Tzanidakis discovered the first clue while combing through telescope data, including observations made by NASA’s SPHERex mission. In 2016, Gaia20ehk looked like a regular, stable star. But about five years later, the light suddenly dipped three times and things quickly turned chaotic.
“Right around 2021, things went completely wrong,” Tzanidakis said. “I can’t stress enough that stars like our sun don’t. So when we saw this one, we thought, ‘Hey, what’s going on here?’
Gaia20ehk’s particular changes – brief dips in brightness and then chaos – had never been observed before, creating a puzzle for the astronomers.
The first clue to what might be happening came from visible light data, which showed that something repeatedly passed in front of the star, blocking parts of the light. But visible light alone couldn’t tell if the culprit was just liquid dust, a starburst, or something far more violent, such as a planet torn apart by the gravity of a supermassive black hole.
To take a closer look, the team analyzed Gaia20ehk’s emissions in the infrared spectrum. As the star’s visible light dimmed and became cluttered, the infrared signal increased, showing that as the system grew fainter, it also grew hotter.
That “could mean the material blocking the star is hot — so hot that it glows in the infrared,” Tzanidakis said.
This finding suggested to the team that a collision between two planets, although rare to see, was most likely, as two planetary bodies could eject hot dust and rock in an orbit that would match their findings.
The scientists believe the planets may not have collided for a single moment. The three early falls of Gaia20ehk may mark grazing encounters as the two bodies spiraled closer together.
“At first they had a range of grazing impacts, which would not produce much infrared energy,” Tzanidakis said. “Then they had their big cataclysmic collision, and the infrared really increased.”
“Andy’s unique work leverages decades of data to find things that happen slowly—astronomical stories that unfold over the course of a decade,” senior author of the study James Davenportan assistant research professor of astronomy at the University of Washington, said in the statement. “There aren’t many researchers looking for phenomena in this way, which means all kinds of discoveries are potentially on the way.”
The team hopes the powerful Simonyi Survey Telescope on Vera C. Rubin Observatory can be used to detect other planetary collisions that may be difficult to spot. Davenport estimates that using Rubin, astronomers could discover 100 new impacts over the next decade. Finding other planetary collisions could help the search for possible habitable worlds that, like Earth, have a moon that helps shield them from asteroids, affects their tides, and has other factors that make the world more inviting.
Besides being rare, the discovery could provide insight into the type of crash that made our moon. Astronomers said the debris cloud around Gaia20ehk is about one astronomical unit from the star — about the same distance as Earth orbits the sun — and that’s one reason the event resembles the giant impact that hit Earth. 4.5 billion years ago.
If that comparison holds, the system could help scientists test the theory that a planetary collision created our moon.
“How rare is the event that created the Earth and the Moon? That question is fundamental to astrobiology,” Davenport said. “Right now, we don’t know how common these dynamics are. But if we catch more of these collisions, we’ll start to find out.”
Tzanidakis, A., & Davenport, J. R. A. (2026). GaIa-GIC-1: an evolving candidate for catastrophic planetesimal collision. The Astrophysical Journal Letters, 1000(1), L5. https://doi.org/10.3847/2041-8213/ae3ddc
