Astronomers May Have Witnessed Two Planets Colliding

Astronomers have caught what appears to be a cosmic catastrophe in progress — two planets colliding around a star roughly 11,000 light-years from Earth.

The star, Gaia20ehk, sits near the constellation Puppis. It's a sun-like main sequence star that should shine steadily. Instead, it started flickering in 2016, then went haywire around 2021. Researchers at the University of Washington determined the dimming wasn't coming from the star itself — vast clouds of hot dust and debris orbiting the system were passing in front of it, blocking light.

"Stars like our sun don't do that," said lead author Anastasios Tzanidakis, a doctoral candidate in astronomy at UW. "When we saw this one, we were like 'Hello, what's going on here?'"

The most likely explanation: a violent collision between two planets, according to research published March 11 in The Astrophysical Journal Letters.

The key evidence came from infrared observations. While visible light from Gaia20ehk dimmed and flickered, infrared light spiked — indicating the blocking material was hot enough to glow in infrared. A catastrophic planetary impact could generate that heat. Earlier, smaller dips in brightness could represent the two planets spiraling closer together before the main collision.

"It's incredible that various telescopes caught this impact in what we're calling real time — meaning the archived data captured the event as it unfolded over years," Tzanidakis said.

The debris cloud orbits at about one astronomical unit — roughly Earth's distance from the sun. That distance, and the nature of the debris, draws an analogy to the impact that may have formed Earth's moon, though researchers stress the comparison is analogical, not confirmed.

Senior author James Davenport, UW assistant research professor of astronomy, noted that not many researchers look for slow-moving astronomical phenomena. "All kinds of discoveries are potentially up for grabs," he said.

The team will continue monitoring Gaia20ehk as the debris cloud settles — a process that could take years or millions of years.

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This article synthesizes reporting from University of Washington and ScienceDaily coverage, with verification against the peer-reviewed paper published in The Astrophysical Journal Letters. The collision interpretation is presented as the researchers' leading hypothesis, not confirmed fact, per editorial guidelines.