Astronomers have spotted a cosmic spectacle: a planetary collision happening 11,000 light-years away. While observing a sun-like star known as Gaia20ehk in the constellation Puppis, they noticed unusual flickers in its light. A massive cloud of hot debris was drifting in front of it, signaling that two planets had collided.
This event reminds us of our own moon’s origins, which formed when a Mars-sized body named Theia crashed into early Earth billions of years ago.
Gaia20ehk’s Unusual Behavior
The detection began when Anastasios Tzanidakis, a PhD candidate at the University of Washington, observed Gaia20ehk behaving strangely. For years, the star shone steadily. But since 2016, it briefly dipped in brightness three times. Then, in 2021, its light became erratic.
Tzanidakis noted, “The star’s light output was nice and flat, but starting in 2016, it had these three dips. Then, it went completely bonkers.” The behavior hinted that something blocking the star’s light was at play, rather than the star itself.
Using infrared telescopes, researchers found the light pattern shifted. The visible light dimmed, but the infrared signals surged. This indicated that the blocking material was extremely hot, reaching around 900 K (about 1,160°F).
The Collision
The early brightness dips likely marked shallow impacts as the two planets spiraled closer together. The massive spike in infrared light pointed to their catastrophic head-on collision, which shattered them into a glowing dust cloud.
The researchers estimated the debris mass at about that of Saturn’s moon Enceladus. This only represents the dust that glows in infrared, meaning the colliding planets were likely much larger.
Echoes of Our Planet’s History
This cosmic event holds significance for understanding our origins. Around 4.5 billion years ago, a similar impact involving a Mars-sized object shaped our moon’s formation.
Right now, the debris around Gaia20ehk orbits at about one astronomical unit—93 million miles from the star—similar to Earth’s distance from the sun. This makes it an excellent target for learning how similar worlds and moons develop.
Tzanidakis expressed his excitement: “It’s amazing that telescopes caught this impact in real time.” Such precise observations are rare due to the need for perfect alignment with Earth. As technology advances, more collisions could be observed.
James Davenport, an assistant research professor at UW, predicts that the new Vera C. Rubin Observatory could uncover 100 similar events in the next decade. He emphasized the importance of this research to understanding planetary formation: “How rare is the event that created the Earth and moon? That question is fundamental to astrobiology.”
The findings appeared in The Astrophysical Journal Letters.
For further reading, you can check the original research article here.
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