Astronomers have captured something extraordinary: the aftermath of a violent collision between large space rocks in another planetary system.
Using NASA’s Hubble Space Telescope, scientists watched what first looked like a distant planet appear, disappear, and then reappear elsewhere—only to realize they were not seeing planets at all, but glowing clouds of debris created by massive cosmic crashes.
The discovery took place in the planetary system surrounding Fomalhaut, a bright star located just 25 light-years from Earth in the southern constellation Piscis Austrinus.
Fomalhaut is larger and more luminous than our sun and is surrounded by vast belts of dust and debris, making it an ideal target for long-term observation.
For more than a decade, astronomers had been tracking a mysterious bright object near the star known as Fomalhaut b.
When it was first detected in 2008, researchers believed it might be an exoplanet—a planet outside our solar system—reflecting light from its host star.
But doubts remained. The object behaved oddly, and its brightness did not quite match expectations for a planet.
In 2023, scientists revisited the system using Hubble. To their surprise, the original bright object had vanished. Even more puzzling, a new bright point of light had appeared nearby.
This sudden change led the research team, including astrophysicist Jason Wang from Northwestern University, to a striking conclusion: neither object was a planet. Instead, both were clouds of dust created by separate collisions between large rocky bodies called planetesimals.
Planetesimals are the building blocks of planets—similar to asteroids in our solar system. When they collide at high speed, they can shatter into vast clouds of fine debris. These clouds can reflect starlight so strongly that, from Earth, they look like planets.
According to the researchers, the first dust cloud, now renamed Fomalhaut cs1, was created by a collision that occurred sometime before 2008. Over the years, the cloud expanded and thinned until it faded from view. The second cloud, Fomalhaut cs2, appears to be the result of a similar collision that happened more recently.
What makes this discovery remarkable is its rarity. Scientists have long believed that collisions between large planetesimals should occur only once every 100,000 years or more in a given system. Yet in Fomalhaut’s system, astronomers witnessed two such events within just 20 years.
“This is the first time we’ve ever seen something like this outside our solar system,” said lead author Paul Kalas of the University of California, Berkeley. “It’s as if we caught two massive car crashes happening almost back-to-back in cosmic terms.”
The finding offers a rare opportunity to study planet formation in action. Planets are thought to grow through countless collisions between smaller bodies, but these processes usually unfold over millions of years. Seeing the debris from such impacts allows scientists to directly observe the materials and dynamics involved in building planets.
The discovery also serves as a warning for future planet-hunting missions. Dust clouds from collisions can closely mimic the appearance of planets, especially when telescopes are searching for worlds by detecting reflected starlight. Without careful analysis, astronomers could mistake these temporary clouds for actual planets.
This insight is especially important as new, more powerful observatories come online. The James Webb Space Telescope (JWST), for example, will soon begin observing the Fomalhaut system in greater detail. Unlike Hubble, JWST can analyze infrared light and provide color information, helping scientists determine the size, composition, and even the presence of ice or water in the dust grains.
Although one of the dust clouds has already faded, researchers plan to continue monitoring the system. By watching how the new cloud evolves, they hope to learn more about the frequency of collisions, the structure of planetary systems, and the processes that shape worlds beyond our own.
In the vastness of space, such dramatic events usually go unseen. This time, however, astronomers were watching—and caught a cosmic crash in the act.
Source: Northwestern University.
