In December 2025, a team of astronomers announced they have captured the first direct images of debris clouds produced by collisions between large objects orbiting the nearby star Fomalhaut. The events—recorded in 2004 and again in 2023—are interpreted as the aftermath of impacts between planetesimals roughly 60 kilometers across. Observers used long-baseline imaging from the Hubble Space Telescope and are now combining those data with follow-up infrared observations to track the evolving clouds. The finding provides a rare, direct window into violent processes that shape planetary systems and may mirror conditions in the young Solar System.
Key Takeaways
- Two discrete dust clouds were observed at Fomalhaut in 2004 and 2023; researchers interpret both as collision aftermaths rather than intact planets.
- Brightness and modeling indicate the colliding bodies were about 37 miles (60 kilometers) or larger—at least four times the estimated size of the Chicxulub impactor that struck Earth 66 million years ago.
- The team estimates roughly 300 million similarly sized planetesimals exist in the region of Fomalhaut where these collisions occurred.
- Carbon monoxide gas has been detected previously in the system, implying the colliders are volatile-rich—more like icy comets than rocky asteroids.
- The 2023 dust cloud is reported to be about 30% brighter than the earlier cloud (noted in 2003/2004 imagery), and observations in August 2025 confirmed it remained visible.
- Paul Kalas and collaborators, building on studies of Fomalhaut since 1993, now argue some point sources formerly labeled as planets (e.g., Fomalhaut b) are transient dust clouds.
- The results were published in Science on Dec. 18, 2025, and teams plan continued monitoring with Hubble and the James Webb Space Telescope.
Background
Fomalhaut, a bright A-type star about 25 light-years from Earth, has long been a focal point for searches of debris and nascent planets. Paul Kalas and colleagues first examined the system with Hubble in the 1990s and identified a prominent circumstellar disk that contains leftover material from planet formation. In 2008 Kalas reported a bright compact source, Fomalhaut b, which was initially promoted as a candidate planet but later raised questions because it did not behave like a typical planet in multiwavelength follow-up.
Over subsequent decades, researchers monitored arcs, clumps and transient features in the outer disk. Improvements in imaging depth and temporal baselines made it possible to distinguish persistent companions from ephemeral dust clouds. The new study interprets the two brightest transient points seen in archival and recent Hubble images as the visible debris from catastrophic collisions between large planetesimals within the disk.
Main Event
The research team compared Hubble exposures taken in 2004 and again in 2023 and identified two similar transient point sources that appeared, evolved and faded on multi-year timescales. Rather than detecting two intact solid bodies striking one another, the observers saw expanding dust clouds produced by those impacts. Photometry and dynamical modeling constrained the minimum sizes of the colliding objects to about 60 kilometers in diameter.
Modelers matched the clouds’ brightnesses, expected expansion speeds and fading rates to collision scenarios and found consistency with high-energy impacts between icy planetesimals. Those impacts would release dust and volatiles—such as water, carbon monoxide and other ices—creating a compact but luminous cloud for years to decades as the debris disperses along the orbit.
Investigators note the 2023 event is roughly 30% brighter than the earlier cloud referenced in archival images and that subsequent follow-up in August 2025 confirmed the cloud remained detectable. The team is combining visible-light Hubble data with planned and ongoing infrared observations from JWST to measure cooling, dust grain sizes and possible gas signatures as the clouds expand.
Analysis & Implications
Directly imaging collision aftermaths around another star gives astronomers an empirical probe of planetesimal populations that would otherwise remain inferred from indirect measures. The minimum-size estimate (≈60 km) places the colliders well above typical small-km comet nuclei and into a regime where self-gravity, porosity and internal composition shape collision outcomes. That helps constrain formation models for outer belts and for the growth of larger planetary bodies.
The inferred population of roughly 300 million similar objects in that annulus implies a dynamically active disk where collisions are frequent enough to produce observable debris over human timescales. Detection of carbon monoxide in the system strengthens the interpretation that many of these bodies are icy and volatile-rich, more analogous to Solar System comets than to inner rocky asteroids.
For exoplanet imaging, the result is a cautionary tale: transient dust clouds can mimic pointlike planets in single-epoch images. Future missions aimed at directly imaging Earth-like worlds, such as the proposed Habitable Worlds Observatory, will need multi-epoch and multiwavelength strategies to distinguish planets from ephemeral debris. Monitoring the evolution of these clouds will also test collision physics used in planetary formation models and refine estimates of disk mass and collisional lifetimes.
Comparison & Data
| Event year | Estimated collider size | Relative brightness |
|---|---|---|
| 2004 (archival) | ≥60 km | Reference cloud |
| 2023 | ≥60 km | ~30% brighter than 2003/2004 reference |
The table summarizes key observational constraints derived from photometry and models: both transient sources require large impactors to reproduce observed luminosities. Scientists derive minimum sizes from the amount of dust needed to reach the measured brightness and from assumptions about impact energy and dust production efficiency. Because those inferences rely on model assumptions about composition and grain properties, the listed sizes are lower limits rather than precise diameters.
Reactions & Quotes
Team members emphasize the novelty of observing collision aftermaths directly and the interpretive care required when classifying point sources around young stars.
“It’s masquerading as a planet because planets also look like tiny dots orbiting nearby stars.”
Paul Kalas, UC Berkeley (lead investigator)
That remark summarizes why Fomalhaut b was debated for years: pointlike appearance alone is insufficient to identify a bound planet without follow-up over time and across wavelengths. Other coauthors highlighted what the collisions reveal about the disk’s inventory.
“This system is a natural laboratory to probe how planetesimals behave when undergoing collisions.”
Mark Wyatt, University of Cambridge (coauthor)
Wyatt and colleagues stress that measured collision rates and debris brightness constrain both size distributions in the belt and the fraction of bodies composed of volatile ices. Outside reactions from the broader community welcomed the directness of the result while urging continued multiwavelength follow-up to reduce model dependence.
Unconfirmed
- Exact compositions of the colliding bodies remain uncertain; volatiles are indicated by prior CO detections but detailed abundances are unmeasured.
- The quoted collider diameters (≈60 km) are lower limits derived from modeling and depend on assumptions about dust production efficiency and grain albedo.
- Whether additional, smaller collisions occur frequently in the inner disk regions has not yet been established by direct imaging.
Bottom Line
This study reports the first direct imaging of collision aftermaths between large planetesimals in another planetary system, using multi-epoch Hubble data and forthcoming JWST follow-up to characterize the debris. The observations imply a populous, icy reservoir around Fomalhaut with many large bodies capable of producing bright dust clouds on observable timescales.
Beyond illuminating planet formation processes, the result cautions astronomers that not all pointlike sources near young stars are planets; distinguishing transient debris from bona fide planets will require repeated, multiwavelength observations. Ongoing monitoring through 2026 and beyond should clarify how these clouds evolve and refine constraints on planetesimal populations in the Fomalhaut belt.