Around the star Fomalhaut, asteroids are involved in collisions that generate massive dust clouds. This is the first time astronomers are witnessing these events, offering insights into the early days of our solar system.

Fomalhaut has had its share of unusual findings. In 2008, Paul Kalas, based on observations from the Hubble Space Telescope in 2004 and 2005, reported a potential giant planet orbiting the young star. Over the years, however, the nature of this peculiar object, dubbed Fomalhaut b, has sparked heated debates. It could either be a planet slightly larger than Jupiter or simply a cloud of debris.

Now, Kalas and his team have revisited Fomalhaut using Hubble. “In 2023, we utilized the same equipment as before, and Fomalhaut b was undetectable. It was effectively gone,” says Kalas, “What appeared was a new Fomalhaut b.”

This new bright feature, named Fomalhaut CS2 (short for “circumstellar light source”), cannot be a planet, as it would have been identified earlier. The leading theory is that it represents a dust cloud resulting from the collision of two large asteroids or planetesimals, each approximately 60 kilometers in diameter. The disappearance of Fomalhaut b implies that it may have been a similar dust cloud all along.

“These sources exhibit noise and instability, so we’re still far from drawing definitive conclusions,” notes David Kipping at Columbia University. “Yet, all existing evidence aligns well with a broader narrative of collisions between protoplanets in nascent systems.”

Interestingly, it’s unexpected to observe such a significant break twice. “The hypothesis suggests that we shouldn’t witness such impacts more than once every 100,000 years, if not even more infrequently. And yet, for some unexplained reason, we seem to observe it twice within 20 years,” Kalas explains. “Fomalhaut lights up like a holiday tree and it’s astounding.”

This might indicate that collisions among planetesimals are occurring more frequently than previously thought, particularly around relatively young stars like Fomalhaut. Kalas and his team plan to conduct further observations over the next three years utilizing both Hubble and the more powerful James Webb Space Telescope (JWST) to track the behavior of Fomalhaut CS2 and attempt to pick up faint signals from Fomalhaut b.

This presents a rare opportunity to witness these collisions first-hand. “To comprehend these violent phenomena, we no longer need to rely solely on theoretical models; we can observe them in real time,” Kalas states. Further observations may enlighten us not only about young planetary systems generally but also about our own early solar system’s position in the cosmic landscape.

“We have long pondered whether the collisions that formed our moon are typical of what occurs throughout the universe, and now we have strong evidence suggesting they are indeed common,” Kipping remarked. “Perhaps we are not as unique as some may assume.”

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