Astronomers have detected evidence of a violent planetary collision around a distant star about 11,000 light-years from Earth, offering one of the clearest observations yet of how planets may collide during the formation of planetary systems.
The discovery began when Anastasios (Andy) Tzanidakis, a doctoral candidate in astronomy at the University of Washington, reviewed archived telescope observations from 2020. While analyzing brightness data, he noticed unusual activity from a star known as Gaia20ehk.
The star lies near the constellation Puppis and is classified as a main-sequence star, similar to the Sun. Stars of this type normally shine with stable and predictable brightness for millions or billions of years.
However, the observations showed that Gaia20ehk behaved very differently. Beginning in 2016, the star’s light briefly dimmed several times. Around 2021, its brightness began fluctuating dramatically.
“The star’s light output was nice and flat, but starting in 2016 it had these three dips in brightness,” Tzanidakis said. “And then, right around 2021, it went completely bonkers.”
Debris cloud reveals violent planetary impact
Scientists later determined that the strange flickering did not originate from the star itself. Instead, large clouds of rock and dust were orbiting the system and passing in front of the star, partially blocking its light.
Further analysis suggested that this debris formed after two planets collided in a violent impact. The crash likely shattered the planets and scattered massive amounts of material into orbit around the star.
“It’s incredible that various telescopes caught this impact in real time,” Tzanidakis said.
Planetary collisions are believed to occur during the early stages of planetary system formation, when young planets frequently crash into each other as their orbits evolve. However, astronomers rarely observe such events directly.
Infrared observations confirm intense heat
Researchers found an important clue when they examined the system using infrared observations. While the star’s visible light flickered and dimmed, the infrared signal increased sharply.
“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.”
This pattern indicated that the debris cloud was extremely hot. Such temperatures are consistent with the intense energy released during a major planetary collision.
Scientists believe the planets may have first experienced smaller grazing impacts as they gradually spiraled toward each other before the final catastrophic crash.
Collision may resemble Earth–moon formation
Researchers say the event may resemble the giant collision believed to have formed the Moon roughly 4.5 billion years ago, when a Mars-sized object struck the early Earth.
In the Gaia20ehk system, the debris cloud appears to orbit its star at about one astronomical unit, roughly the same distance between Earth and the Sun.
Over time, the scattered material could cool and merge into new planetary bodies. Scientists say the process could eventually produce a system similar to the Earth–moon pair.
Future telescopes may detect more planetary impacts
The findings were published in The Astrophysical Journal Letters. Astronomers say new surveys may soon detect more events like this. The NSF-DOE Vera C. Rubin Observatory is expected to begin its Legacy Survey of Space and Time later this year.
According to estimates by James Davenport of the University of Washington, the observatory could detect around 100 similar planetary collisions over the next decade.
Researchers say finding more examples could help scientists better understand how planets form and how often Earth-like worlds emerge across the galaxy.
