Science News from research organizations Astronomers think they just witnessed two planets colliding Astronomers may have witnessed a dramatic planetary collision around a distant star—possibly a replay of the event that created Earth’s moon. Date: March 11, 2026 Source: University of Washington Summary: Astronomers have caught what may be a rare cosmic catastrophe unfolding 11,000 light-years away. A seemingly ordinary sun-like star suddenly began flickering wildly, puzzling scientists until they realized the strange dimming was caused by vast clouds of hot dust and debris drifting across the star. The most likely explanation is a violent planetary collision—two worlds smashing together and scattering glowing material throughout the system. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY Lead author Andy Tzanidakis’ rendering of the planetary collision he suspects occurred around star Gaia20ehk in 2021. Credit: Andy Tzanidakis Anastasios (Andy) Tzanidakis was reviewing archived telescope observations from 2020 when he noticed something unusual. A seemingly ordinary star called Gaia20ehk was behaving in a way astronomers rarely see. Located about 11,000 light years from Earth near the constellation Pupis, Gaia20ehk is a stable "main sequence" star similar to our sun. Stars of this type typically shine with steady, predictable brightness. Instead, this one began flickering erratically. "The star's light output was nice and flat, but starting in 2016 it had these three dips in brightness. And then, right around 2021, it went completely bonkers," said Tzanidakis, a doctoral candidate in astronomy at the University of Washington. "I can't emphasize enough that stars like our sun don't do that. So when we saw this one, we were like 'Hello, what's going on here?'" Evidence Points to a Massive Planetary Collision Researchers eventually determined that the strange behavior was not coming from the star itself. Instead, huge amounts of rock and dust were passing in front of the star as they orbited the system, partially blocking the light traveling toward Earth. The debris appeared to have been created by an extraordinary event: a violent collision between two planets. "It's incredible that various telescopes caught this impact in real time," Tzanidakis said. "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. If we can observe more moments like this elsewhere in the galaxy, it will teach us lots about the formation of our world." The team's analysis was published March 11 in The Astrophysical Journal Letters . Why Planetary Collisions Happen Planet formation is a chaotic process. Around young stars, gravity pulls together material such as dust, gas, ice, and rocky debris that orbit the star. In the early stages of a solar system, collisions between growing planetary bodies are common. Some worlds smash together, while others are thrown outward into space. Over tens of millions of years, this process gradually shapes and stabilizes planetary systems like our own. Even though these collisions are likely common in the universe, witnessing one from Earth is extremely difficult. To detect it, the orbiting debris must pass directly between us and the star, blocking some of its light. The resulting dimming pattern can unfold slowly, sometimes over several years. "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," said senior author James Davenport, a UW assistant research professor of astronomy. "Not many researchers are looking for phenomena in this way, which means that all kinds of discoveries are potentially up for grabs." Infrared Signals Reveal Hot Debris Tzanidakis, the study's lead author, focuses on stars that show dramatic changes in brightness over time. Earlier research at the University of Washington helped identify a system where a binary star and a large dust cloud produced an eclipse lasting seven years. Gaia20ehk, however, presented a completely different puzzle. Its brightness first dipped briefly and then became extremely chaotic. Scientists struggled to explain the pattern until Davenport suggested examining observations taken in infrared light instead of visible light. "The infrared light curve was the complete opposite of the visible light," Tzanidakis said. "As the visible light began to flicker and dim, the infrared light spiked. Which could mean that the material blocking the star is hot -- so hot that it's glowing in the infrared." A violent planetary collision could easily generate that level of heat. Such an event would also explain the earlier dips in brightness that astronomers observed. "That could be caused by the two planets spiraling closer and closer to each other," Tzanidaki