- \n
- A grad student was looking through old data<\/strong> when he spied something unusual.<\/li>\n
- The data revealed the collision of 2 exoplanets,<\/strong> 11,000 light-years away.<\/li>\n
- Astronomers hope to detect about 100 similar collisions<\/strong> in the coming decade, using the new Rubin Observatory in Chile. It\u2019s important because this collision might be similar to the one that formed Earth\u2019s moon. And Earth\u2019s moon is key to life.<\/li>\n<\/ul>\n
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Collision of 2 exoplanets found in old data<\/h3>\n
An astronomy grad student at the University of Washington \u2013 Anastasios Tzanidakis \u2013 was looking through old telescope data when he noticed something odd. It was a seemingly ordinary star, called Gaia20ehk, flickering wildly in brightness. Intrigued, he and his colleagues investigated further. And they determined that the flickering was due to large amounts of hot dust and rocks passing in front of the star. They concluded the flickering of the star must indicate a catastrophic collision between two of its planets, 11,000 light-years away. <\/p>\n
Tzanidakis said in a statement:<\/p>\n
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The 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?\u2019<\/p>\n
It\u2019s incredible that various telescopes caught this impact just as the light of the collision reached Earth. 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. <\/p>\n
If we can observe more moments like this elsewhere in the galaxy, it will teach us lots about the formation of our world.<\/p>\n<\/blockquote>\n
Tzanidakis and his collaborator, James Davenport, published their findings in the peer-reviewed Astrophysical Journal Letters<\/em> on March 11, 2026.<\/p>\n
Chaos in early planetary systems<\/h3>\n
Stars form from rotating disks of gas and dust. Afterwards, there\u2019s a leftover disk of material called a protoplanetary disk. And at first this disk contains just dust, gas, ice and rocks. But, over millions of years, the materials in the disk coalesce, under gravitational forces. So planets and other small bodies, such as asteroids and comets, form out of the disk. <\/p>\n
Conditions with the disk of an early stellar system can be chaotic. Planets can collide and shatter. Or the force of an impact could hurl a planet out of its stellar system. But eventually, over a timescale of 100 million years or so, the new-born solar system settles into a stable state.<\/p>\n
Collisions between newly formed extrasolar planets are likely quite common. But catching one in the act is hard. That\u2019s because \u2013 in a scenario like the one detected by Anastasios Tzanidakis and colleagues \u2013 telescopes can detect the flickering starlight only if the orbiting collision debris is in the line of sight between us and the star.<\/p>\n
Star system Gaia20ehk <\/h3>\n
The star system Gaia20ehk is about 11,000 light-years from Earth. It\u2019s near the direction of the constellation Puppis the Stern. It\u2019s in a stable phase of its evolution, known as the main sequence phase. That means the star is steadily burning hydrogen to helium in its core. <\/p>\n
![\"A](\"https:\/\/earthsky.org\/upl\/2026\/03\/Gaia20ehk-in-the-sky-Tzanidakis-Univ-Washington.jpg\")
Gaia20ehk is at the center of this image. A small region of the field is shown in the inset box with the star marked by orange crosshairs. It\u2019s about 11,000 light-years from Earth, near the direction of the constellation Pupis the Stern. Image via NASA\/NSF NOIRLab\/ University of Washington.<\/figcaption><\/figure>\n Looking in both visible and infrared<\/h3>\n
For a long time, as viewed through earthly telescopes, Gaia20ehk shone with a steady light. But starting in 2016, Tzanidakis said, there were three dips in its brightness. Then, in 2021, the star\u2019s brightness became erratic.<\/p>\n
Davenport suggested they examine this star at infrared wavelengths. And the results were a revelation. Tzanidakis commented:<\/p>\n
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The infrared light curve was the complete opposite of the visible light. As the visible light began to flicker and dim, the infrared light spiked. Which could mean that the material blocking the star is hot \u2014 so hot that it\u2019s glowing in the infrared.<\/p>\n<\/blockquote>\n
But what caused the dips in light before 2021? Tzanidakis said:<\/p>\n
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That could be caused by the two planets spiraling closer and closer to each other. At first, they had a series of grazing impacts, which wouldn\u2019t produce a lot of infrared energy. Then, they had their big catastrophic collision, and the infrared really ramped up.<\/p>\n<\/blockquote>\n
![\"Two](\"https:\/\/earthsky.org\/upl\/2026\/03\/Gaia20ehk-light-curve-Tzanidakis-Univ-Washington.png\")
The plot at the top shows Gaia20ehk\u2019s brightness in visible light. There were 3 small dips that were followed, in 2021, by a chaotic variation in brightness. Meanwhile, the bottom plot shows brightness in infrared wavelengths for the same time period. Note that the infrared brightness increased significantly when the visible light brightness was chaotic. Image via Tzanidakis et al.\/ The Astrophysical Journal Letters\/ University of Washington.<\/figcaption><\/figure>\n Could a similar collision have created our moon?<\/h3>\n
Some scientists think that a similar collision might have created our moon. They say that about 4.5 billion years ago, an object the size of Mars collided into Earth, ripping out material from our young planet to form the moon.<\/p>\n
Gaia20ehk is only slightly more massive than our sun. In addition, the orbiting material causing the star\u2019s fluctuating brightness is about one astronomical unit from the star. So whatever happened in this system to create the debris is located in this star system at about the same distance between our sun and Earth-moon system. <\/p>\n
The researchers think the hot debris could, at that distance, eventually cool down enough to create a system similar to our Earth and moon. But they won\u2019t know for sure until the dust literally settles, which could take a few million years. <\/p>\n
- The data revealed the collision of 2 exoplanets,<\/strong> 11,000 light-years away.<\/li>\n