Planet formation is not a gentle process. In young star systems, growing worlds often collide, break apart, and come back together. Collisions in distant solar systems are common, but spotting one requires patience and luck. The planets need to pass directly in front of their star for the debris to dim its light, and that flicker occurs over several years.<\/p>\n
In 2020, Anastasios (Andy) Tzanidakis, a doctoral candidate in astronomy at the University of Washington, was reviewing old telescope data when he noticed something unusual. A star called Gaia20ehk, about 11,000 light-years away near the constellation Puppis, was behaving strangely. Normally, as a stable \u2018main sequence\u2019 star<\/a> like our sun, it should shine steadily. Instead, it began flickering wildly.<\/p>\n He said, \u201cThe star\u2019s 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. I can\u2019t emphasize enough that stars like our sun don\u2019t do that. So when we saw this one, we were like \u2018Hello, what\u2019s going on here?\u201d<\/p>\n The flickering wasn\u2019t caused by the star itself. Instead, massive amounts of rocks and dust were orbiting the system, blocking its light in patches. The likely source was extraordinary, a catastrophic collision between two planets.<\/p>\n \u201cIncredibly, telescopes caught this impact in real time,\u201d said Tzanidakis. \u201cOnly a handful of planetary collisions<\/a> have ever been recorded, and none resemble so closely the one that formed Earth and the moon<\/a>. Observing more events like this could reveal much about how our world came to be.\u201d<\/p>\n Tzanidakis, who studies extreme changes in starlight, had previously identified a binary star system with a dust cloud that caused a seven-year eclipse. But Gaia20ehk posed a new puzzle. Its strange pattern, brief dips in brightness followed by chaos, had never been seen before. This debris, heated to nearly 900 degrees Kelvin, blocks the star\u2019s light in patches while glowing brightly in infrared.<\/p>\n The breakthrough came when Davenport suggested checking infrared data. Unlike the visible light, which dimmed and flickered, the infrared light spiked.<\/p>\n \u201cThat means the material blocking the star is so hot it glows in infrared,\u201d Tzanidakis explained.<\/p>\n Such heat points to a cataclysmic planetary collision, which could also explain the initial dips in light.<\/p>\n Tzanidakis explained that the flickering could be caused by two planets spiraling toward each other. At first, they grazed each other, producing little infrared energy. Then came the catastrophic collision, and the infrared light surged.<\/p>\n Clues suggest this impact is similar to the one that formed Earth and the moon 4.5 billion years ago. The dust cloud around Gaia20ehk orbits at about 1 astronomical unit, which is the same distance as Earth from the sun. Over time, that material could cool and solidify into a system like ours, though this process might take years or even millions. It weighs about 4 \u00d7 10\u00b2\u2070 kilograms.<\/p>\n For now, the discovery highlights the need to find more collisions. The Vera C. Rubin Observatory\u2019s upcoming survey could detect up to 100 new impacts in the next decade, helping scientists understand how planets, and potentially habitable worlds, form.<\/p>\n \u201cHow rare was the Earth\u2013moon collision?\u201d Davenport asked<\/a>. \u201cThat\u2019s a fundamental question for astrobiology. The moon may be one of the key ingredients that make Earth so good for life<\/a>, from tides and weather to shielding us from asteroids. If we can catch more of these events, we\u2019ll start to learn how common those dynamics really are.\u201d<\/p>\n Journal Reference:<\/p>\n