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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →Hubble did not capture two planets colliding. It detected compact dust sources near the star Fomalhaut, and astronomers interpret them as debris clouds created when planetesimals—smaller bodies that can help build planets—collided. The bodies involved may have been tens of kilometers across, making the events enormous, but their size is inferred from models rather than directly seen.
What did Hubble actually see?
Fomalhaut, about 25 light-years from Earth, is a bright star surrounded by dusty belts. Hubble had previously detected a compact source known as Fomalhaut b, now called cs1. The research team interprets cs1 not as light reflected from a planet but as a cloud of dust. While looking for it, the team found a second source, cs2, in 2023. Earlier Hubble observations had not detected cs2, and its appearance resembles cs1 at an earlier stage. NASA’s December 18, 2025 report and the authors’ Science paper describe the evidence and interpretation.
The observations are changing points of light against a debris belt—not footage of an impact. The collision explanation fits the sources’ appearance and, in cs1’s case, its movement. The paper reports that cs1’s radial velocity component increased from 3.4 km/s in 2010–2012 to 11.7 km/s in the following year, consistent with stellar radiation pressure pushing very small dust grains outward.
How violent was the inferred collision?
NASA quoted co-author Mark Wyatt of the University of Cambridge estimating that the planetesimals destroyed to create cs1 and cs2 were about 37 miles (60 kilometers) across. He also estimated that about 300 million such objects orbit Fomalhaut. These are population and dust-model estimates, not individual bodies resolved by Hubble.
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The paper’s estimates depend on assumptions about grain density, the distribution of grain sizes, and the roughly 20-year interval inferred between events. In one model using a size-distribution slope of 3.5, the authors estimate parent bodies for cs1-like events at roughly 30 km in radius. Other tested slopes, 3 and 4, produce substantially different estimates and are discussed by the authors as less plausible for different reasons. The paper’s conditional radius estimate and NASA’s approximate 60-km-across figure are broadly similar in scale, but are not identical measurements or necessarily the same model quantity.
For a sense of the cloud itself, the paper estimates that cs1’s optical brightness requires about 5 × 1022 cm2 of dust cross-sectional area and a total dust mass around 1020 g under its stated assumptions. Small grains dominate the brightness: grains up to about 3 micrometers in radius are estimated to make up roughly 10% of the mass and can be driven out of the system by radiation pressure. These values are model-derived, not a direct measurement of the cloud’s mass.
How strong is the evidence for a collision?
The interpretation rests on indirect evidence: the compact sources’ appearance, their emergence between observations, and cs1’s outward acceleration. That makes a collision-generated dust cloud the researchers’ explanation—not a directly observed event. The timing and arrangement leave open questions.
- When cs2 formed: It could have appeared at any point in the nine years after Hubble’s last observation in 2014. A September 2024 follow-up produced a candidate source with a signal-to-noise ratio around 3, but its sensitivity was limited and the authors do not treat it as a conclusive identification.
- Whether the sources are linked: Their close placement does not prove a shared dynamical origin. The paper estimates a 10% chance that a second source would fall within the stated observed region by chance and discusses alternative dynamical explanations.
Why are two events in about 20 years surprising?
The team’s inferred mean interval between cs1-like events in Fomalhaut is about 20 years. That contrasts sharply with prior theoretical expectations, cited by NASA, of one collision every 100,000 years or longer. As principal investigator Paul Kalas put it: “Previous theory suggested that there should be one collision every 100,000 years, or longer. Here, in 20 years, we’ve seen two,”
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11The discrepancy makes Fomalhaut a valuable case for studying debris from collisions, a basic process in planetary-system evolution. It does not establish that large collisions happen at this rate around other stars; the estimate is specific to Fomalhaut and to the team’s interpretation and assumptions.
How does Fomalhaut compare with other reported collisions?
Dust and light can reveal different kinds of impact aftermaths, but separate systems should not be conflated:
- HD 166191: NASA’s 2022 report described Spitzer observations of infrared brightening and a transiting debris cloud attributed to a collision involving dwarf-planet-sized objects.
- ASASSN-21qj: NASA’s 2024 explainer covered a different proposed collision around a young Sun-like star. Infrared brightening followed by prolonged dimming was interpreted as a hot debris cloud crossing the star; researchers proposed that the colliding objects were planets several to tens of Earth masses.
Those cases use different observations and support different estimates. In particular, the planet-mass proposal for ASASSN-21qj does not describe the Fomalhaut bodies.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What observations were planned next?
At the time of NASA’s December 2025 report, the team had been granted Hubble time to monitor cs2 over the following three years and planned observations with Webb’s NIRCam. NASA said Webb’s near-infrared color information could help researchers estimate dust-grain size and composition, including whether the cloud contains water ice. Those were plans reported at that time, not confirmation that the observations have since taken place.
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