\u201cI would have had to have been the luckiest astronomer in the world to see it,\u201d Kalas told Gizmodo in a video call, \u201cbecause these collisions only happen once every 100,000 years.\u201d<\/p>\n
Fomalhaut and the luckiest astronomer <\/p>\n
Kalas and Fomalhaut go way back. The astronomer first studied the star as a student in 1993 and identified the exoplanet candidate Fomalhaut b from continued observations. In addition, he discovered a large belt of dusty debris roughly 133 astronomical units (AU) from the host star (1 AU is the average distance from the Earth to the Sun, so this band is quite far from its host star).<\/p>\n
![\"Dss](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/12\/fomalhaut-sts-313x336.jpg\")
Fomalhaut, captured by the Hubble Space Telescope. Credit: NASA\/ESA\/Digitized Sky Survey 2\/Davide De Martin (ESA\/Hubble) <\/p>\n
In 2002, study co-author Mark Wyatt<\/a> devised mathematical models that suggested large objects in the dust belt should occasionally collide and light up, but very rarely.\u00a0And when they do, \u201cthey\u2019ll create little points of light that we will be able to observe,\u201d Wyatt, an astrophysicist at Cambridge University in the United Kingdom, told Gizmodo during a phone call.<\/p>\n Then, two years later, Kalas spotted Fomalhaut b. At the time, the object moved very much like an exoplanet, leading Kalas and other astronomers to conclude that it was a planet. But there was some controversy over if it really was\u2014or, for that matter, if it even existed.<\/p>\n \u201cSome people called it a zombie planet,\u201d recalled Kalas. Then around 2013, astronomers noticed that Fomalhaut b\u2019s path had curved away from a star, more like tiny particles comprising a dust cloud, not a solid planet.<\/p>\n \u201c[A] planet can\u2019t appear out of nowhere. But a dust cloud can.\u201d <\/p>\n Finally, the \u201cplanet\u201d disappeared from sight<\/a>, and the community concluded that the object must have been an expanding dust cloud. Accordingly, NASA\u2019s official exoplanet archive removed<\/a> Fomalhaut b from the list in 2020.<\/p>\n Fomalhaut b, 2.0? <\/p>\n But the story was far from over. Three years after the disappearance of Fomalhaut b\u2014renamed \u201ccircumstellar source 1,\u201d or cs1\u2014Kalas found \u201canother Fomalhaut b,\u201d he said. \u201cAnd the reason we say it solved the mystery [of Fomalhaut b] is because a planet can\u2019t appear out of nowhere. But a dust cloud can.\u201d<\/p>\n Here\u2019s what that means. The intense swirling of matter around Fomalhaut clumps up into asteroid-like objects big enough to collide and create a giant dust cloud. This cloud reflects light\u2014just like a planet\u2014so it \u201cmasquerades as a planet for a while,\u201d Kalas explained. Eventually, the cloud becomes less dense, and radiation from the host star pushes it out of orbit, making the signal vanish.<\/p>\n In a similar vein, the 2023 source, cs2, recently emerged from another rare yet sizable asteroid collision. The impact poofed up into a radiant dust cloud observable by our telescopes, just as Wyatt predicted in 2002. But as he himself admitted, the new observation did come as a surprise.<\/p>\n \u201cWell, I knew that the model was right, but the model being right doesn\u2019t mean that you can actually detect that,\u201d Wyatt admitted.<\/p>\n The cosmic laboratory <\/p>\n The familiarity of asteroid collisions betrays the fact that, scientifically speaking, humanity hasn\u2019t been able to directly see it happen, Kalas said. \u201cYou see animations of collisions\u2014like, the asteroid hitting Earth and wiping out the dinosaurs,\u201d he said. \u201cAsteroid collisions are inferred or fantasized about. These are the first observations in astronomy [that], in real time, we are seeing the collision happen.\u201d<\/p>\n ![\"Fomalhaut](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/12\/fomalhaut-system-cs1-cs2-comparison.jpg\")
A composite Hubble image showing the debris ring and dust clouds surrounding Fomalhaut. Credit: NASA\/ESA\/Paul Kalas (UC Berkeley)\/Joseph DePasquale (STScI) <\/p>\n![\"Fomalhaut](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/12\/Fomalhaut_planetesimal_collision_4k-1280x720.jpg\")
An artist\u2019s interpretation of the collision of two planetesimals in the debris disk of Fomalhaut. Credit: Thomas M\u00fcller (MPIA) <\/p>\n