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. “In 2023, we used the same instrument we’d used [before], and we did not detect Fomalhaut b – it wasn’t visible anymore,” says Kalas. “But what really shocked us was [that] there was a new Fomalhaut b.”

This new bright spot, called Fomalhaut cs2 (short for “circumstellar source”), couldn’t 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.

“These sources are noisy and erratic, so we’re still some ways off a firm conclusion,” says at Columbia University. “But, all of the evidence to date seems to fit neatly under the umbrella explanation of collisions between proto-planets in a nascent system.”

Spotting two such smash-ups is unexpected, though. “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,” says Kalas. “Fomalhaut is sparkling like a holiday tree, and that is a surprise.”

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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. “We no longer have to depend solely on theory to understand these violent impacts; we can actually see them,” 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.

“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,” says Kipping. “Perhaps we’re not as unusual as some have speculated.”

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Earth may owe some of its properties to a nearby star that blew up just as the solar system was forming. This pattern, which saw a supernova bubble envelop the sun and shower it with cosmic rays, may be ubiquitous across the galaxy – implying there could be a far greater number of Earth-like planets than previously thought.

We know, thanks to ancient meteorite samples, that the solar system used to be filled with heat-producing radioactive elements that quickly decayed. The heat from these elements drove off large amounts of water from the space rocks and comets that came together to form Earth, ensuring the planet had the right amount of water for life to later develop.

It is unclear, however, how these elements reached the solar system. Many of them are commonly found in supernova explosions, but simulations of close-by supernovae have struggled to produce the exact ratios of radioactive elements inferred from meteorite samples to have been present in the early solar system. One problem is that these nearby blasts may also have been so powerful that they would have blown apart the fragile early solar system before any planets had formed.

Now, at the University of Tokyo in Japan and his colleagues have found that a supernova could have provided the necessary radioactive ingredients for Earth without upsetting the planet formation process, as long as it was slightly further away.

In their model, a supernova that is around 3 light years from the solar system could produce the required radioactive elements in a two-stage process. Some, such as radioactive aluminium and manganese, would be produced directly in the supernova and then travel on shock waves from the exploded star to reach the solar system.

Then, high-energy particles called cosmic rays emanating from the supernova would follow behind these shock waves and hit other atoms in the solar system’s still-forming disc of gas, dust and rocks, a process that would produce the remaining radioactive elements needed, such as beryllium and calcium. “Previous models of solar system formation focused only on the injection of matter. I realised we were ignoring the high-energy particles,” says Sawada. “I thought, ‘What if the young solar system was simply engulfed in this particle bath?’”

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Because this process works with a supernova that is further away than previous studies, Sawada and his team estimate that between 10 to 50 per cent of sun-like star and planetary systems could have been seeded with radioactive elements in this way and produced planets with Earth-like abundances of water. For previous models, with close-by supernovae, being hit was “like winning the lottery”, says Sawada. But moving the supernova further away implies that “the recipe for Earth is likely not a rare accident, but a universal process happening all over the galaxy,” he says.

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“It’s quite novel, because it’s a fine balance between destruction and creation,” says at Cardiff University, UK. “You need the right elements and the right distance.”

If this mechanism is correct, it could help guide future searches for Earth-like planets by planned telescopes like NASA’s Habitable Worlds Observatory, by looking for traces of ancient supernovae and finding star systems that were close to them at the time, says Inserra.

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