Astronomers have observed a collision between two large asteroids orbiting the young star Fomalhaut, creating a new dust cloud that resolves the long-standing mystery of an apparent planet. This event, captured by the Hubble Space Telescope, suggests similar collisions may have shaped early planetary systems like our own. The discovery highlights unexpected activity around this nearby star.
The star Fomalhaut, located just 25 light-years from Earth, has long puzzled astronomers with its debris disks and anomalous features. In 2008, observations from the Hubble Space Telescope in 2004 and 2005 revealed what appeared to be a giant planet, dubbed Fomalhaut b, larger than Jupiter. Subsequent data sparked debate: was it a planet or merely a transient dust cloud?
Recent Hubble imaging in 2023 brought clarity. Paul Kalas at the University of California, Berkeley, and his team found Fomalhaut b had vanished, but a new bright spot, Fomalhaut cs2, had emerged. "In 2023, we used the same instrument we’d used [before], and we did not detect Fomalhaut b – it wasn’t visible anymore," Kalas explained. "But what really shocked us was [that] there was a new Fomalhaut b."
Analysis indicates Fomalhaut cs2 is dust from a smash-up between two planetesimals, each about 60 kilometers across. The fading of the original Fomalhaut b points to it being a similar collision remnant. David Kipping at Columbia University noted, "These sources are noisy and erratic, so we’re still some ways off a firm conclusion. But, all of the evidence to date seems to fit neatly under the umbrella explanation of collisions between proto-planets in a nascent system."
Such events are rare by theory—occurring perhaps once every 100,000 years—yet two have been spotted around Fomalhaut in just two decades. "Theory dictates that you shouldn’t see these collisions except once every 100,000 years or rarer. And yet, for some reason, we’ve seen 2 events in 20 years," Kalas said. "Fomalhaut is sparkling like a holiday tree, and that is a surprise."
Upcoming observations with Hubble and the James Webb Space Telescope over the next three years will track these changes. "We no longer have to depend solely on theory to understand these violent impacts; we can actually see them," Kalas added. Kipping suggested this offers insights into our solar system's formation, including the moon-forming impact: "We’ve long wondered if the moon-forming impact was typical or not beyond our cosmic shore, and here we see compelling evidence that collisions are par for the course. Perhaps we’re not as unusual as some have speculated."