Around the nearby star Fomalhaut, asteroids are smashing into each other in a series of cosmic cataclysms, creating huge clouds of dust. For the first time, astronomers are watching one of these collisions as it occurs, which could provide a window into the early days of our own solar system.
Fomalhaut has a history of strange observations: in 2008, at the University of California, Berkeley, and his colleagues reported what seemed to be a giant planet in orbit around the young star, based on observations with the Hubble Space Telescope made in 2004 and 2005. Over the years, though, as more observations have rolled in, researchers have hotly debated over what this strange object, called Fomalhaut b, might be. It was either a planet a bit larger than Jupiter, or a cloud of debris.
Now, Kalas and his team have used Hubble to look at Fomalhaut once again. āIn 2023, we used the same instrument weād used [before], and we did not detect Fomalhaut b ā it wasnāt visible anymore,ā says Kalas. āBut what really shocked us was [that] there was a new Fomalhaut b.ā
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This new bright spot, called Fomalhaut cs2 (short for ācircumstellar sourceā), couldnāt be a planet, or it would have been seen sooner. The best explanation is that it is a cloud of dust created by the collision of two large asteroids, or planetesimals, each around 60 kilometres in diameter. The disappearance of Fomalhaut b hints that it was probably a similar dust cloud all along.
āThese sources are noisy and erratic, so weāre still some ways off a firm conclusion,ā says at Columbia University. āBut, all of the evidence to date seems to fit neatly under the umbrella explanation of collisions between proto-planets in a nascent system.ā
Spotting two such smash-ups is unexpected, though. āTheory dictates that you shouldnāt see these collisions except once every 100,000 years or rarer. And yet, for some reason, weāve seen 2 events in 20 years,ā says Kalas. āFomalhaut is sparkling like a holiday tree, and that is a surprise.ā
It may mean that collisions between planetesimals are more common than we had thought, at least around relatively young stars like Fomalhaut. Kalas and his colleagues have more observations scheduled over the next three years with both Hubble and the more powerful James Webb Space Telescope (JWST) to watch how Fomalhaut cs2 behaves moving forward and to try to find the now-dimmer Fomalhaut b.
This is a unique opportunity to study these collisions in real time. āWe no longer have to depend solely on theory to understand these violent impacts; we can actually see them,ā says Kalas. More observations could teach us not just about young planetary systems in general, but also about our own early solar system and where it fits in the cosmic menagerie.
āWeāve 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,ā says Kipping. āPerhaps weāre not as unusual as some have speculated.ā
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Spend a weekend with some of the brightest minds in science, as you explore the mysteries of the universe in an exciting programme that includes an excursion to see the iconic Lovell Telescope.
Mysteries of the universe: Cheshire, England
