Astronomers have directly observed a second planetary collision around the star Fomalhaut, located just 25 light-years from Earth. The event, captured by the NASA/ESA Hubble Space Telescope, adds to growing evidence that planetesimal impacts are far more frequent in some systems than previously thought. This makes Fomalhaut’s system a unique natural laboratory for studying the chaotic early stages of planetary formation.
The Discovery of a Second Collision
The star Fomalhaut, already known for its large debris disk and a previously detected (but now disputed) planet called Fomalhaut b, revealed a new point source of light in 2023. This newly observed object, dubbed “cs2,” appeared in the same region around the star where Fomalhaut b was first spotted two decades earlier. Researchers, led by Dr. Paul Kalas from the University of California, Berkeley, interpret this as a dust cloud resulting from a recent high-energy collision between two planetesimals – rocky bodies smaller than planets but larger than asteroids.
Why this matters: Direct observation of such collisions is exceedingly rare. Unlike our own Solar System, which has largely settled into orbital stability, Fomalhaut appears to be undergoing frequent and violent planetary evolution.
The Mystery of Recurring Impacts
The discovery is puzzling because the two observed collisions – cs1 and cs2 – are physically close to each other within Fomalhaut’s debris disk. If impacts were truly random, they should occur across a wider area. The fact that they’ve happened within a 20-year span is also unusual.
Previous models suggested such events should occur only once every 100,000 years or longer. The fact that two have been witnessed in quick succession suggests either an unstable configuration within the system or a higher collision rate than anticipated.
Implications for Planetary System Formation
Scientists estimate the colliding planetesimals were roughly 30 kilometers (19 miles) in diameter. Based on these observations, they infer the existence of approximately 300 million similar objects orbiting Fomalhaut. This high density of planetesimals suggests a chaotic early stage of system development.
“The exciting aspect of this observation is that it allows researchers to estimate both the size of the colliding bodies and how many of them there are in the disk, information which is almost impossible to get by any other means,” said Dr. Mark Wyatt of the University of Cambridge. The ongoing collisions provide a unique opportunity to study planetesimal composition and formation mechanisms in real time.
“Fomalhaut’s planetary system would be sparkling with these collisions” — Dr. Paul Kalas
The study, published in Science, reinforces the idea that planetary systems evolve through frequent, violent interactions early in their lives. These collisions shape the distribution of debris, influence planetary orbits, and ultimately determine the final architecture of a star system.
The Fomalhaut system offers a rare glimpse into this turbulent phase, providing valuable insights into how planets form and how common such chaotic environments might be throughout the galaxy.
